Following two years work and more than a handful of meetings, the Association of Noise Consultants (ANC) published the draft version of the “AVO Guide” in February 2018.  This Guide marks a significant step forwards in the assessment of internal environmental conditions in residential developments, and hence invites the industry to step up to the design challenge.  TEK, with their new range of products to enable natural ventilation in noisier environments, are demonstrating their position at the forefront of meeting this new design challenge.

The AVO Guide enables and encourages developers to design new dwellings in a way that considers the effects of both thermal comfort and acoustic comfort at the same time.  Traditionally, these issues have been considered separately, so that occupants of new dwellings that are exposed to high levels of environmental noise are forced to choose between comfortable temperatures with the windows open, or comfortable and safe noise levels with the windows closed.  Jack Harvie-Clark and Anthony Chilton presented the draft in a CIBSE webinar that you can watch. Jack presented the draft Guide at the CIBSE Symposium in April 2018 – you can download the supporting paper on the CIBSE website here.

Sustainable development

We have known for some time that we need sustainable, resilient dwellings that are comfortable for the occupants.  We know that people like simple controls over their environment; the act of opening a window or vent is intuitive to meet a need for ventilative cooling and for air movement to increase the cooling effect.  There is a clear conflict between the benefits of opening windows, and the risks associated with excessive noise.  A fragmented design approach results in residential accommodation that may be uncomfortable to occupants, and hence may be considered unsustainable. Residual risks for stakeholders include:

  • Health & wellbeing risks for occupants
  • Design risks for consultants; and
  • Legal risks for developers

Designing for internal environmental quality

Historically, external noise considerations and facade sound insulation have been deliberately excluded from Building Regulations, as they are site-specific issues.  The Planning system is therefore currently seen as the regulatory regime with the best opportunity to require concurrent consideration of noise and thermal comfort, even though these issues would seem to sit within the remit of Building Regulations.  In the past there have only been occasional Planning requirements to consider the indoor noise and mitigation of overheating in an integrated, holistic manner.  With the previous lack of appropriate design criteria and little explanation of the issues in the complex and inter-related fields, it has been difficult for Planners and Environmental Health practitioners to specify suitable requirements.  Apex Acoustics has demonstrated that in 85% of planning applications, the acoustic designers assumed that windows were closed to provide acceptable acoustic conditions, while the mechanical designers assumed windows were open to provide acceptable thermal conditions.

Design criteria

The Association of Noise Consultants’ draft Acoustics, Ventilation & Overheating: Residential Design Guide, addresses these issues.  This ground-breaking guide proposes allowing tolerances over the annual average internal noise level limits that are normally applied to new dwellings, for the reduced portion of the year when opening windows may be required to mitigate overheating.  It suggests a balanced approach, such that if the overheating risk is lower – with less reliance on opening windows, for less frequent periods – then it is suggested that occupants may accept slightly higher noise levels.  If there is a high reliance on opening windows, such that they are required for a greater proportion of the year, then a lower noise level limit would be more appropriate.  The identification of design criteria enables the industry to respond by developing the most advantageous solutions – such as those by TEK Ltd.  In many locations where new residential development is desirable opening windows permit excessive external noise ingress, and attenuated vents may be a more appropriate solution.  The draft Acoustics, Ventilation & Overheating: Residential Design Guide provides a framework for assessment and separate criteria to associate with both ventilation and provision of thermal comfort.  External noise is treated separately from internal (building services) sources of noise, because people respond to these different noise sources in different ways.

Contents of the AVO Guide

The AVO Guide includes:

  • an explanation of ventilation requirements under the building regulations as described in ‘Approved Document F – Means of Ventilation, 2010 Edition’ (‘ADF’) along with typical ventilation strategies and associated noise considerations;
  • an explanation of the overheating assessment methodology described in CIBSE ‘Design methodology for the assessment of overheating risk in homes’ (TM59);
  • acoustic criteria and guidance relating to different ventilation and overheating conditions, for both environmental noise ingress and building services noise; and
  • a worked example of the application of the AVO Guide including indicative design solutions.

We look forward to developing the most advantageous solutions for future residents, so that people can enjoy thermal comfort within their homes without being subject to harmful and annoying levels of noise.  TEK’s new range of products offers a designers a real opportunity to achieve comfortable conditions for residents within sustainable, resilient buildings.

Jack Harvie-Clark, Apex Acoustics Ltd.

1. Introduction

1.1 Acknowledgements

1.1 The guide has been prepared with contributions from members of the Association of Noise Consultants Acoustics, Ventilation and Overheating (AVO) Group.

1.2 The principle authors of the guide include:

  • Anthony Chilton, Max Fordham (Chair of Working Group)
  • Andrew Long, Sandy Brown
  • David Trew, Bickerdike Allen Partners
  • Jack Harvie-Clark, Apex Acoustics
  • James Healey, WSP
  • Mathew Hyden, Cundall
  • Nick Conlan, Apex Acoustics
  • Stephen Turner, Stephen Turner Acoustics

1.3 Additional support was provided by the following AVOG committee members:

  • Adrian Passmore, Arup Acoustics
  • Barry Jobling, Hoare Lea
  • Ian MacArthur, Clarke Saunders Acoustics
  • John McCullough, Mid Kent Shared Service
  • Juliette Paris-Newton, Robin Mackenzie Partnership
  • Mark Scaife, MLM Group
  • Michael Swainson, BRE
  • Robert Osborne, ANC

1.2 Foreword

1.4 This Acoustics, Ventilation and Overheating Guide (‘AVO Guide’) is intended for use by practitioners and designers. It recommends an approach to acoustic assessments for new residential development that takes due regard of the interdependence of provisions for acoustics, ventilation, and overheating. Application of the AVO Guide is intended to demonstrate good acoustic design as described in the ProPG:

Planning & Noise, May 2017 [1] (‘ProPG’), when considering internal noise level guidelines.

1.5 Indoor environmental quality is dependent on air quality (and hence ventilation), thermal comfort and acoustic comfort. These factors are clearly interdependent but, due to lack of guidance, are generally only addressed independently. Provisions for both ventilation and mitigation of overheating may include façade openings that permit external noise ingress, and/or mechanical equipment that generates noise. In both cases, there is potential for noise impact.

1.6 Traditionally, the provision of façade sound insulation to protect against outdoor sound has been considered separately from the ventilation strategy and any strategy for mitigating overheating. This approach can lead to different designers making different, incompatible assumptions. The AVO Guide aims to assist designers to adopt an integrated approach to the acoustic design within the context of the ventilation and thermal comfort requirements.

1.7 A requirement to assess and provide mitigation against outdoor sound for a residential development may be invoked through the planning system; thus the local planning authority may be responsible for assessing and enforcing the proposed mitigation. The need for, and provision of adequate ventilation is outlined in building regulations, and therefore managed through the building control system. Although there is currently no statutory requirement to assess the potential for overheating in dwellings as part of the building regulations, an assessment may be undertaken to meet planning and/or the developer’s requirements. Hence, as well as being undertaken by different designers, the adequacy of the provisions for each aspect may be assessed by different bodies and potentially based on different requirements. To date, this disparate approach to design and assessment has not facilitated an integrated approach to the consideration of internal conditions that residents experience.

1.8 The evolution of energy performance requirements under building regulations has led to increased air tightness and enhanced thermal insulation. However, these changes can have unintended consequences. Internal air quality can be poor unless ventilation systems are effective, whereas the efficacy of ventilation systems in leakier buildings was of less consequence. When there is an increased capacity to retain heat, dissipation of excessive heat gains can become more problematic, with the consequential increase in overheating risk. Other factors currently contributing to overheating risk include climate change and the urban heat island effect. Regional temperatures are set to rise and micro-climates around buildings can cause temperatures to be significantly above regional levels. Air temperatures may therefore be significantly different over the course of the life of buildings currently being developed.

1.9 A fragmented design approach results in accommodation that may be uncomfortable to occupants, and hence may be considered unsustainable. Residual risks for stakeholders include:

  • Health & wellbeing risks for occupants
  • Design risks for consultants; and
  • Legal risks for developers.

1.10 The increasingly urgent need for an integrated approach to consider noise, ventilation, and overheating has been the motivation to produce the AVO Guide. The purpose of this document is to help avoid these risks by delivering accommodation that is fit for purpose, comfortable and sustainable.

1.3 Overview of Document

1.11 The AVO Guide includes:

  • an explanation of ventilation requirements under the building regulations as described in ‘Approved Document F – Means of Ventilation, 2010 Edition’ [2] (‘ADF’) along with typical ventilation strategies and associated noise considerations;
  • an explanation of the overheating assessment methodology described in CIBSE ‘Design methodology for the assessment of overheating risk in homes’ [3] (‘TM59’);
  • potential acoustic criteria and guidance relating to different ventilation and overheating conditions, for both environmental noise ingress and building services noise; and
  • a worked example of the application of the AVO Guide including indicative design solutions.

1.12 There is currently no specific quantitative guidance within the AVO Guide on assessing the impact of individual events using the Lmax parameter during the overheating condition due to insufficient evidence being currently available on which to base analysis, although this is usually required in practice.

1.4 Scope

1.13 The AVO Guide is intended for the consideration of new residential development that will be exposed predominantly to airborne sound from transport sources, and to sound from mechanical services that are serving the dwellings in question. Other sources of noise, such as noise from industrial, commercial or entertainment premises, and of ground-borne noise and vibration, are outside the scope of the AVO Guide. New apartments, flats and houses are the most common type of new residential development; however, the approach may also be used for other types of residential development such as residential institutions, care homes etc.

1.14 The AVO Guide seeks to:

  • encourage an assessment of noise that recognises the interdependence between the acoustics, ventilation and overheating designs;
  • provide a means of assessment to satisfy the need to consider acoustics, ventilation and overheating at the planning stage;
  • assist in educating clients, environmental health/planning officers and other stakeholders of the interdependence of design for acoustics, ventilation and overheating.

1.15 Although the policy coverage is limited to England, the approach may be applicable in other parts of the UK. This document assumes the user has general knowledge of acoustics and standard terminology.

1.16 The external air quality environment may also impact on the ventilation strategy adopted, and influence selected locations for any external air inlets. This aspect is outside the scope of the AVO Guide

1.17 There are other benefits for occupants from opening windows, such as the connection with the outside, sense of fresh air, perception of draughts when overheating, and sense of control over one’s environment. Consideration of these factors is beyond the scope of the AVO Guide.

1.5 Good Acoustic Design

1.18 The ProPG emphasises the importance and principles of good acoustic design; the AVO Guide is intended to contribute to the practice of good acoustic design. It is noted that the over-arching aspiration of good acoustic design is that residents may open windows without any adverse acoustic impact (ProPG para. 2.33); where a site layout achieves these conditions, the portion of the AVO Guide relating to environmental noise becomes effectually redundant.

1.19 In particular, the paragraphs 2.34 – 2.36 of the ProPG indicate that an integrated design approach must be taken to acoustic, ventilation and thermal comfort conditions:

  • Para 2.34: ‘design the accommodation so that it provides good standards of acoustics, ventilation and thermal comfort’
  • Para 2.36: ‘[where a] scheme is reliant on open windows to mitigate overheating, it is also necessary to consider the potential noise impact during the overheating condition. In this case a more detailed assessment of the potential impact on occupants should be provided in the ADS’.

1.20 In addition, Para 2.38 says: ‘Where mechanical services are used as part of the ventilation or thermal comfort strategy for the scheme, the impact of noise generated by these systems on occupants should also be assessed’.

1.21 The AVO Guide provides a practical method to address these requirements.

1.22 Good acoustic design may be considered as a component of sustainable design. Other aspects of sustainable design include a response to climate change, in terms of aiming to minimise use of energy and other resources.

1.23 The London Plan Policy encourages the design of places and spaces to avoid overheating and excessive heat generation, and to reduce overheating due to the impacts of climate change. Major development proposals should reduce potential overheating and reliance on air conditioning systems and demonstrate this in accordance with the cooling hierarchy identified. The cooling hierarchy seeks to reduce any potential overheating and also the need to cool a building through active measures. Air conditioning systems are a very resource intensive form of active cooling, increasing carbon dioxide emissions.

1.24 In accordance with sustainable design and construction principles, development proposals should, amongst other things, maximise opportunities to orientate buildings and streets to minimise summer and maximise winter solar gains; use trees and other shading; increase green areas in the envelope of a building, including its roof and environs; and maximise natural ventilation. These sustainable design principles mirror good acoustic design as described in the ProPG.

1.25 To assist the reader, a glossary of terminology used throughout this document is provided.

1.6 Application of this Guide

1.26 The practical application of the AVO Guide is described in Appendix B. The starting position when considering mitigation of noise impact on new residential development is to apply good acoustic design, site-wide, as described in the ProPG.

1.27 Prior to further developing the design, the acoustician should highlight this to the wider design team/developer. The role of the acoustician is then to assist the team in developing options to suitably control external noise ingress in conjunction with adequate ventilation and mitigation of overheating.

1.28 There is a need to address how:

  • The ventilation strategy impacts on the acoustic conditions.
  • The strategy for mitigating overheating impacts on the acoustic conditions, and whether a more detailed overheating assessment is required to inform this.

1.29 The guidance in Appendix B aims to:

  • help acousticians prepare suitable advice for developers and their design teams so that informed decisions can then be made on how best to progress designs.
  • assist local planning authorities to seek evidence of appropriate design details and of post-completion verification, to comply with suitably-worded planning conditions.
  • enable a consistent and practical approach to considering noise impact under different ventilation and overheating conditions.
  • outline where there is evidence for risks of adverse noise effects and the need for balanced consideration with other aspects of indoor environmental quality when developing the design of new homes.

2. Relevant Legislation and Guidance

2.1 This chapter presents some of the key legislation, policy and guidance relevant to ventilation, overheating and acoustics.

2.1 Ventilation

2.2 Ventilation requirements for dwellings are covered under the Building Regulations ADF.

2.3 ADF describes three types of ventilation provision and associated ventilation rates for dwellings. The types of ventilation are summarised in Table 2-1.

2.4 It is important to differentiate between the need to provide ‘purge ventilation’ as required occasionally under Part F, which applies to all building types, in all locations and throughout the year; against the need to provide ventilation for the ‘overheating condition’ which is influenced by the location, orientation, type and design of the building and may be required for sustained periods of time, or not at all, depending on the overheating risk.

2.5 The document then goes on to state that:

‘Ventilation may also provide a means to control thermal comfort but this is not controlled under the Building Regulations’.

2.6 ADF provides details of four template ‘Systems’ which comply with the above strategy for new dwellings and can be adopted to demonstrate compliance.

2.7 These ‘Systems’ are summarised in Table 2-2 and further details are provided in Appendix A. See note to Table 3-1 and notes at A.8 and A.9.

2.8 Note that System 2 is rarely used in practice.

Table 2-1 ADF types of ventilation required


Note 1 – ‘Whole Dwelling Ventilation’ is often confused with ‘background ventilation’, a term used in the 1995 version of ADF. In the current ADF, the term ‘background ventilator’ refers to trickle vents.

Table 2-2 ADF template Systems

2.2 Overheating

2.9 Overheating is a growing concern but there are no specific requirements relating to overheating

in the building regulations. Both ADF and Approved Document L1A of The Building Regulations briefly mention overheating but do not provide details on what constitutes overheating.

2.10 For the purposes of this document, overheating is taken to mean:

‘the phenomenon of excessive or prolonged high temperatures in homes, resulting from internal or external heat gains, which may have adverse effects on the comfort, health or productivity of the occupants.’ [4]

2.11 The gaps in appropriate criteria and assessment methodology were identified by the Zero Carbon Hub (2015) and they called for a domestic overheating methodology to be produced. This led to the development of TM59.

2.12 TM59 sets out a methodology for predicting temperatures inside dwellings and provides overheating compliance criteria which are discussed further in Appendix A. It provides a standardised approach to predicting overheating using dynamic thermal modelling and acknowledges that the methodology is necessarily prescriptive to enable it to be consistently applied.

2.13 To undertake the assessment, information on the heat loads, thermal properties of the building construction, weather data and methods of providing ventilation are required.

2.14 An overheating assessment may not always be undertaken and reference could be made to TM59 Section 2.1 which provides guidance based on the risk of overheating.

2.15 TM59 notes:

‘This methodology is proposed for all residences and should especially be considered for:

— large developments

— developments in urban areas, particularly in southern England

— blocks of flats

— dwellings with high levels of insulation and air-tightness

— single aspect flats.

Individual houses and developments with a low risk of overheating may not require the use of dynamic thermal modelling.

Professional judgement must be used when taking the decision to omit dynamic thermal modelling to test overheating. The risk must be considered in the context of the project and the decision should be taken jointly with the client, design team and planners. A list of risk factors for identifying properties at high risk of overheating is provided in Energy Planning — Greater London Authority guidance on preparing energy assessments [5] and in BRE’s Home Quality Mark [6].’

2.16 Alternative assessment methods such the Passive House Planning Package [7] (PHPP) may also be suitable for assessing overheating if considered appropriate for the specific project.

2.17 Developments will normally (but not always) require additional ventilation (above ADF whole dwelling ventilation provisions) in order to mitigate overheating. Where an overheating assessment is undertaken, it should provide details as to the duration and rate of any additional ventilation required to meet overheating compliance criteria. Where this additional ventilation is provided passively, the overheating assessment should also provide information about the required size of façade openings.

2.18 See Appendix A2 for a list of output data from a dynamic thermal model that may be necessary to undertake the acoustic assessment.

2.3 Acoustics

2.3.1 Current planning policy, regulations and guidance

2.19 Noise management is a devolved issue. This means that, although there are many similarities, different policies and regulations apply in England, Wales, Scotland and Northern Ireland. In England, the overarching policy on noise management is set out in the Noise Policy Statement for England [8] (‘NPSE’). The NPSE contains the vision of promoting good health and a good quality of life through the effective management of noise within the context of Government policy on sustainable development.

2.20 The NPSE also contains three aims:

‘Through the effective management and control of environmental, neighbour and neighbourhood noise within the context of Government policy on sustainable development:

  • avoid significant adverse impacts on health and quality of life;
  • mitigate and minimise adverse impacts on health and quality of life; and
  • where possible, contribute to the improvement of health and quality of life.’

2.21 In the explanatory note to the NPSE, reference is made to concepts from toxicology that had previously been applied to noise impacts, for example, by the World Health Organisation. They are:

  • No Observed Effect Level (NOEL) which is the level below which no effect can be detected;
  • Lowest Observed Adverse Effect Level (LOAEL) which is the level above which adverse effects on health and quality of life can be detected.

2.22 The explanatory note goes on to introduce the concept of a Significant Observed Adverse Effect Level (SOAEL) which is the level above which significant adverse effects on health and quality of life occur.

2.23 Although for both LOAEL and SOAEL, the word ‘level’ is used, this does not mean that the impact can only be described as an individual noise level. It could also include factors such as the number of times the noise impact occurs, the duration of the impact, and the time of day the impact occurs. Thus, depending on the circumstance, the noise impact could be managed by reducing how often it occurs rather than just reducing the level of impact when it does occur.

2.24 The NPSE states that it is not possible to have a single objective noise-based measure that defines SOAEL that is applicable to all sources of noise in all situations. Consequently, the SOAEL is likely to be different for different noise sources, for different receptors and at different times.

2.25 The explanatory note confirms that the first aim of the NPSE states that significant adverse effects on health and quality of life should be avoided while taking account of the guiding principles of sustainable development. The second aim refers to the situation where the impact lies somewhere between LOAEL and SOAEL. To meet this aim requires that all reasonable steps should be taken to mitigate and minimise adverse effects on health and quality of life while also taking into

account the guiding principles of sustainable development. The explanatory note goes on to state that this does not mean that such adverse effects cannot occur.

2.26 With regard to land-use planning in England, the relevant policy is primarily set out in the National Planning Policy Framework [9] (‘NPPF’).

2.27 For noise, the requirements are set out as follows:

‘Planning policies and decisions should aim to:

  • Avoid noise from giving rise to significant adverse impacts on health and quality of life as a result of new development;
  • Mitigate and reduce to a minimum other adverse impacts on health and quality of life arising from noise from new development, including through the use of conditions;
  • Recognise that development will often create some noise and existing businesses wanting to develop in continuance of their business should not have unreasonable restriction put on them because of changes in nearby land uses since they were established; and
  • Identify and protect areas of tranquillity which have remained relatively undisturbed by noise and are prized for their recreational and amenity value for this reason.’

2.28 Elsewhere, the NPPF states that the planning system should contribute to and enhance the natural and local environment by:

‘Preventing both new and existing development from contributing to or being put at unacceptable risk from, or being adversely affected by unacceptable levels of ’…. ’noise pollution.’

2.29 The implementation of the policies in the NPPF is supported by a suite of web-based guidance, including the Planning Practice Guidance on Noise [10] (‘PPG(N)’). It includes a table which summarises the noise exposure hierarchy based on the likely average response. The Noise Exposure Hierarchy is reproduced in Table 2-3.

Table 2-3 Summary of noise exposure hierarchy based on the likely average response (from PPG(N))


Note 1 – Since the publication of the NPSE, there have been some who assert that ‘avoid’ means ‘not occur’. That is not a correct interpretation of policy. The use of the word ‘avoid’ recognises that there might be situations where the social and economic benefits of the development outweigh the significant adverse impact or effect that occurs. However, these would be exceptional occurrences.

2.30 The PPG(N) makes it clear that noise can override other planning concerns. It points out, though, that neither the NPSE nor the NPPF expects noise to be considered in isolation, separately from the economic, social and other environmental dimensions of proposed development.

2.31 In clarifying how the term ‘the context of Government policy on sustainable development’ should be interpreted, some assistance can be obtained from the Government decision letter associated with the Thames Tideway Tunnel project. In that letter, it is stated that:

‘The National Planning Policy Framework, the National Planning Practice Guidance on noise and the Noise Policy Statement for England are all clear that noise management should be determined in the context of sustainable development including the environmental, economic and social benefits of the proposal.’

2.32 In their local development plans, Local Planning Authorities (LPAs) can include exposure values as standards for various situations. These values tend to be set at exposures which correspond to LOAEL. The PPG(N), however, states that care should be taken to avoid these standards from being implemented as fixed thresholds as specific circumstances may justify some variation being allowed.

2.33 Furthermore, as mentioned above, the explanatory note to the NPSE states that the policy does not mean that adverse effects arising from noise cannot occur.

2.34 Not all development is required formally to seek planning consent from the relevant Local Planning Authority (LPA). Some proposals fall under the terms of Permitted Development Rights (PDR). The definition of those developments which can be promulgated under PDR is set out in Statutory Instrument 2015/596. This order was amended by SI 2016/332 requiring that, in the case of a change of use of offices to dwelling houses, the developer must apply to the LPA for a determination as to whether the prior approval of the authority will be required as to

‘impacts of noise from commercial premises on the intended occupiers of the development.’

2.35 In that order, commercial premises are defined as:

‘any premises normally used for the purpose of any commercial or industrial undertaking which existed on the date of the application, and includes any premises licensed under the Licensing Act 2003 or any other place of public entertainment.’

2.36 This definition means that there is no formal requirement for a developer to determine whether prior approval is needed regarding any noise from transportation sources affecting such a change of use. However, it may be in the interests of the developer to consider the transportation noise impacts and the associated ventilation issues with such a change of use.

2.37 For Nationally Significant Infrastructure Projects promulgated under the Planning Act 2008, the relevant policy is set out in the topic specific National Policy Statements (NPS). For noise, the policies in the various NPSs reflect the NPSE.

2.3.2 Guidance on the effects of noise

2.38 As indicated in the NPSE, objective values associated with SOAEL will depend on the specific circumstances. More information can be derived for values associated with LOAEL from existing guidance. Relevant examples are set out below.

BS 8233:2014 [11]

2.39 This standard provides a wide range of guidance regarding sound insulation and noise reduction in buildings. In the Foreword, it states that:

‘As a guide, this British Standard takes the form of guidance and recommendations. It should not be quoted as if it were a specification or a code of practice and claims of compliance cannot be made to it.’

2.40 Table 4 of BS 8233 sets out desirable internal noise levels resulting from steady external sources. These are reproduced in Table 2-4.

Table 2-4 Indoor ambient noise levels for dwellings (reproduced from Table 4 of BS 8233)

2.41 These levels are accompanied by various notes including:

  • The levels are based on existing guidelines issued by the World Health Organisation [12]
  • They assume normal diurnal fluctuations in external noise
  • The levels are based on annual average data and do not have to be achieved in all circumstances. For example, it is normal to exclude and occasional events such as fireworks night and New Year’s Eve
  • If relying on closed windows to meet the guide values, there needs to be an appropriate alternative ventilation that does not compromise the façade insulation or resulting noise level. If applicable, any room should have adequate ventilation (e.g. trickle ventilators should be open) during assessment
  • Where a development is considered necessary or desirable, the levels in Table 2-4 may be relaxed by up to 5 dB and reasonable internal conditions still achieved.

2.42 It is now generally regarded that the values in Table 4 of BS 8233 represent LOAEL in that situation.

2.43 BS 8233 also sets out the maximum steady noise levels that can permit reliable speech communication. These are reproduced in Table 2-5.

Table 2-5 Maximum steady noise levels for reliable speech communication (reproduced from Table 7 of BS 8233)

2.44 The values from this table can be used to estimate the extent of the noise impact on speech communication.

ProPG: Planning & Noise 2017

2.45 The ProPG was prepared in 2017 by a group comprising members representing the Chartered Institute of Environmental Health (CIEH), the Institute of Acoustics (IOA) and the Association of Noise Consultants (ANC).

2.46 This document provides technical guidance on how to assess, primarily, the impact of transportation noise on new residential development. It is designed to assist with the implementation of existing planning policy.

2.47 The ProPG promotes the use of ‘Good Acoustic Design’ as a primary noise management measure to optimise the acoustic environment that would be experienced by the residents. It recognises that there will be some situations where there would be a need to rely on closed windows and associated ventilation in order to achieve the desired acoustic outcome. In that situation it states that

‘special care must be taken to design the accommodation so that it provides good standards of acoustics, ventilation and thermal comfort without unduly compromising other aspects of the living environment. In such circumstances, internal noise levels can be assessed with windows closed but with any façade openings used to provide “whole dwelling ventilation” in accordance with Building Regulations Approved Document F (e.g. trickle ventilators).’

2.48 The document also states that

‘It should also be noted that the internal noise level guidelines are generally not applicable under “purge ventilation” conditions as defined by Building Regulations Approved Document F, as this should only occur occasionally (e.g. to remove odour from painting and decorating or from burnt food).’

2.49 The document continues

‘In addition to providing purge ventilation, open windows can also be used to mitigate overheating. Therefore, should the LPA accept a scheme is to be assessed with windows closed, but this scheme is reliant on open windows to mitigate overheating, it is also necessary to consider the potential noise impact during the overheating condition. In this case a more detailed assessment of the potential impact on occupants should be provided in the ADS.’

2.50 It concludes that:

‘It should be noted that overheating issues will vary across the country and any specific design solutions will need to be developed alongside advice from energy consultants.’

WHO Night Noise Guidelines for Europe [13]

2.51 Within these guidelines it is stated that Lnight,outside 40 dB is equivalent to the LOAEL for night noise.

2.52 The guidelines also suggest that Lnight,outside above 55 dB represents a situation that is considered increasingly dangerous for public health.

2.53 This value is increasingly being regarded as a SOAEL in that situation.

Individual Noise Events

2.54 The WHO Guidelines for Community Noise [12] (WHO 1999) provide advice regarding the impact of individual noise events on sleep. They state that:

‘For a good sleep, it is believed that indoor sound pressure levels should not exceed approximately 45 dB LAmax more than 10–15 times per night.’

2.55 The LAmax is considered with the fast time-weighting.

2.56 This impact is being increasingly regarded as a LOAEL for this situation.

2.57 More recent research in presented in Aircraft noise effects on sleep: Application of the results of a large polysomnographic field study [14] has examined the probability of additional awakenings caused by individual noise events. This combines the number of events and the maximum level of those events inside the bedroom. It may be possible to use this approach to evaluate a SOAEL in relation to individual noise events.

2.58 Appendix A of ProPG also gives a helpful overview with regard to assessing the effect of individual noise events.

Dose Response Relationship

2.59 Any acoustic guidelines should not be regarded as fixed thresholds. In reality, there is a continuous relationship between the noise level and the resulting effects. There are many academic studies which investigate the dose-response relationships between environmental noise and effects on humans including annoyance, speech interference, sleep disturbance and other health effects. A good overview of studies can be found in Adverse effects of noise exposure on health – a state of the art summary [15].

2.60 Assessing noise exposure for public health purposes [16] gives useful information regarding the relative effect on subjective sleep quality resulting from difference types of transport noise sources (road, rail and air). Annoyance from transportation noise: Relationships with exposure metrics DNL and DENL and their confidence intervals [17] gives similar information in relation to annoyance. Reference 4 relates the probability of awakenings to internal LASmax levels. Beoordeling van geluidpieken in de woonomgeving [18] relates speech interference to levels.

2.61 It should be noted that the strength of the evidence varies between studies and some

relationships are based on indirect meta-analysis of other studies or re-casting of data based on a series of assumptions. In each case reference is made to the relevant study and the reader is recommended to consult the reference to fully understand the underlying research.

3. Internal Ambient Noise Level Guidelines

3.1 This chapter presents guidance regarding indoor ambient noise levels in new residential development that will be exposed predominantly to airborne sound from transport sources, and to sound from mechanical systems serving the development.

3.2 The contribution to internal noise levels from transport sources and from mechanical services are considered separately and independently, because there is evidence that occupants have a different tolerance to each. Section 3.1 considers transport noise sources and Section 3.2 considers mechanical services noise.

3.3 For both sources of noise, the guidance makes a clear distinction between the situation where ventilation is being provided as defined by ADF whole dwelling ventilation (‘ADF ventilation condition’) and the situation where measures are in place to mitigate overheating to meet agreed compliance criteria (‘overheating condition’).

3.4 In terms of noise effect, the important distinction between these two situations is that the ADF ventilation condition applies for the entire time whereas the overheating condition applies only for part of the time.

3.5 In the case of noise from mechanical services, the guidance for the overheating condition makes reference to existing guidance documents. In the case of noise from transport sources, there is no appropriate existing guidance for the overheating condition. Instead, the guidance presented here considers the suitability of higher internal ambient noise levels in terms of the effect on occupants.

3.1 Internal Ambient Noise Levels due to Transport Noise Sources

3.1.1 Introduction

3.6 It is suggested here that the desirable internal noise standards within Table 4 of BS 8233 should be achieved when providing adequate ventilation as defined by ADF whole dwelling ventilation. However, it is considered reasonable to allow higher levels of internal ambient noise from transport sources when higher rates of

ventilation are required in relation to the overheating condition.

3.7 The basis for this is that the overheating condition occurs for only part of the time and occupants may accept a trade-off between acoustic and thermal conditions given that they have some control over their environment i.e. at their own discretion, they may be more willing to accept higher short-term noise levels in order to achieve better thermal comfort.

3.8 It is important to note that there is no specific research available to support this view regarding human response to combined exposure to heat and noise. However, the notion that control over one’s environment moderates the response to exposure is accepted in the field of thermal comfort, and underpins the adaptive thermal comfort model.

3.9 The suitability of higher internal ambient noise levels has been considered in terms of various effects such as:

  • Daytime annoyance
  • Daytime interference with activities (conversation/telephone)
  • Night time sleep disturbance (using average noise level parameters such as LAeq)
  • Night time sleep disturbance (using parameters for individual noise events LAmax /SEL).

3.10 The threshold between “Low” and “Medium” risk for both daytime and night-time conditions are derived by consideration of BS 8233 desirable internal levels, relaxed by 5 dB as described in ProPG to represent reasonable internal conditions.

3.11 The threshold between “Medium” and “High” risk for daytime conditions is derived by the consideration that LAeq,T 50 dB represents an upper threshold for reasonable internal daytime conditions.

3.12 The threshold between “Medium” and “High” risk for night-time is based on the WHO Night Noise guidelines, which state that for external levels above LAeq,T 55 dB

‘adverse health effects occur frequently and a sizeable proportion of the population is highly annoyed and sleep-disturbed’.

3.13 The threshold values in Tables 3-2 and 3-3 are related by the assumption that there is a 12 dB difference between external free-field noise levels and internal ambient noise levels. Refer to 3.20 for further discussion.

3.14 It should be noted that, although the importance of considering the effect of individual noise events for the overheating situation is acknowledged, no quantitative guidance is included in the current version of this document. Reference should be made to Appendix A of ProPG.

3.15 The effect of increased internal ambient noise from transport noise sources will depend both on the absolute noise level and the amount of time that an increased ventilation rate is required to control overheating. A good design process should therefore, as a priority, seek to minimise heat gains thereby reducing the amount and duration of ventilation required to control overheating and the consequential effect from increased ingress of noise.

3.16 Appropriate research work is urgently needed to better inform the guidance for the overheating condition.

3.1.2 Approved Document F (ADF) Ventilation Condition

3.17 Recommendations for desirable internal ambient noise levels for ADF ventilation conditions are set out in Table 3-1.

3.1.3 Overheating Condition

3.18 A two-level assessment procedure is recommended to estimate the potential impact on occupants in the case of the overheating condition. Refer to Figure 3-1.

3.19 The Level 1 assessment is sufficient for developments on ‘Low’ or ‘Medium’ risk sites (as defined by Table 3-2). The Level 2 assessment is suggested for ‘High’ risk sites.

3.20 The Level 1 assessment is based around the scenario where a partially open window is used to control overheating. The values presented are external free-field noise levels; an assumed outside-to-inside level difference of 15 dB has

been taken into account for partially open windows (WHO 1999) with a -3 dB conversion from facade to free-field level (BS 5228-1 [19]). This level difference is considered representative of typical domestic rooms with simple façade openings of around 2% of the floor area. It should be noted that this area of opening is not necessarily sufficient to mitigate overheating in all design cases and, should the design under consideration deviate significantly from this situation, then the levels should be adjusted accordingly.

3.21 In those instances where ventilative cooling is used, it is worth noting that ventilation rates are typically an order of magnitude higher than those associated with ADF whole dwelling ventilation.

3.22 The noise levels suggested in Tables 3-2 and 3-3 assume a steady road traffic noise source but may be adapted for other types of transport.

Table 3-1 Indoor Ambient Noise Levels resulting from transport noise sources – ADF ventilation condition


Note 1 – ADF has a clearly defined objective definition of purge ventilation to rapidly dilute pollutants and/or water vapour. This is defined as 4 air changes per hour in Appendix A of the Approved Document. This is used for occasional activities such as painting and decorating or accidental releases such as smoke from burnt food or spillage of water. Purge ventilation can also be used to improve thermal comfort. This is not controlled under the Building Regulations. Purge ventilation may form one part of a design strategy to control the risk of overheating. The level of ventilation required to control overheating will depend on the details of the individual room and dwelling and can be different than the 4 air changes per hour required to dilute pollutants/water vapour.

Note 2 – For Systems 1 and 2, the background ventilators are sized for the winter period as described in Tables 5.2a, b of ADF. For Systems 3 and 4, the systems are sized for the winter period. If additional ventilation is required to control excess humidity in warmer months, appropriate consideration should be given to the resulting internal ambient noise levels under this condition.

Figure 3-1 Two-level noise assessment procedure – overheating condition

Table 3-2 Guidance for Level 1 assessment of noise from transport noise sources relating to overheating condition


Note 1 – The values presented in this table should not be regarded as fixed thresholds and reference can also be made to relevant dose-response relationships, such as those described in a DEFRA 2014 study [20].

Note 2 – A decision must be made regarding the appropriate averaging period to use. The averaging period should reflect the nature of the noise source, the occupancy profile and times at which overheating might be likely to occur. Further guidance can be found within the 2014 IEMA Guidelines [21].

Note 3 – Regular individual noise events should also be considered. Refer to Appendix A of ProPG for further guidance.

Note 4 – The risk of an adverse effect occurring will also depend on how frequently and for what duration the mitigation of overheating is likely to result in increased internal noise levels.

Table 3-3 Guidance for Level 2 assessment of noise from transport noise sources relating to overheating condition

Internal ambient noise level [Note 1]

Examples of Outcomes

Risk category for Level 2 assessment [Note 4]

LAeq,T [Note 2] during 07:00 – 23:00 [Note 5]

LAeq,8h [Note 3] during 23:00 – 07:00

≤ 35 dB

≤ 30 dB

Noise can be heard, but does not cause any change in behaviour or attitude. Can slightly affect the acoustic character of the area but not such that there is a perceived change in the quality of life.

Negligible

> 35 dB and ≤ 40 dB

> 30 dB and ≤ 35 dB

Noise can be heard and causes small changes in behaviour and/or attitude, e.g. turning up volume of television; speaking more loudly; where there is no alternative ventilation, having to close windows for some of the time because of the noise. Potential for some reported sleep disturbance. Affects the acoustic environment inside the dwelling such that there is a perceived change in the quality of life.

Low

> 40 dB and ≤ 50 dB

> 35 dB and ≤ 43 dB

Increasing risk of adverse effect due to impact on reliable speech communication during daytime or sleep disturbance at night.

Although noise levels at the lower end of this category will cause changes in behaviour, they may still be considered suitable.

Noise levels at the upper end of this category will result in more significant changes in behaviour and are only likely to be considered suitable if they occur for limited periods.

Medium

> 50 dB

> 43 dB

The noise causes a material change in behaviour and/or attitude, e.g. avoiding certain activities during periods of intrusion; where there is no alternative ventilation, having to keep windows closed most of the time because of the noise. Potential for sleep disturbance resulting in difficulty in getting to sleep, premature awakening and difficulty in getting back to sleep. Quality of life diminished due to change in acoustic character of the area.

High

Note 1 – The values presented in this table should not be regarded as fixed thresholds and reference can also be made to relevant dose-response relationships such as those described in a DEFRA 2014 study.

Note 2 – A decision must be made regarding the appropriate averaging period to use. The averaging period should reflect the nature of the noise source, the occupancy profile and times at which overheating might be likely to occur. Further guidance can be found within the 2014 IEMA Guidelines.

Note 3 – Regular individual noise events should also be considered. Refer to Appendix A of ProPG for further guidance.

Note 4 – The risk of an adverse effect occurring will also depend on how frequently and for what duration the mitigation of overheating is likely to result in increased internal noise levels.

Note 5 – The daytime levels presented in this table may not be appropriate for residential care homes or other situations where conditions for daytime resting are known, at the design stage, to be of particular importance.

3.2 Internal Ambient Noise Levels from Mechanical Services

3.2.1 Introduction

3.23 Human hearing response, annoyance and the health-related effects of noise are of primary concern when considering building services noise in dwellings. Research presented in Understanding the role of inhabitants in innovative mechanical ventilation strategies [22], Ventilation in new homes – A report of site findings [23], Why this crisis in residential ventilation? [24], The relationship between health complaints, the quality of indoor air and housing characteristics [25], Mechanical ventilation in recently built Dutch homes: technical shortcomings, possibilities for improvement, perceived indoor environment and health effects [26] and How loud is too loud? Noise from domestic mechanical ventilation systems [27], demonstrates that occupants will adjust mechanical ventilation systems to a level of noise that is tolerable, or disable it entirely. Either of these actions result in insufficient ventilation; the adverse effects of this include poor indoor air quality and reduced thermal comfort for the occupants.

3.24 While these studies are examples of how occupants respond to the noise from the equipment, the actual noise levels or the character of the noise that people may tolerate are not well documented in the literature. The guidance values in this chapter assume steady noise levels without distracting characteristics.

3.25 There is also very little information relating to the use of mechanical systems which use ambient air to control overheating (ventilative cooling), and very few examples of it being used in the UK. Mechanical systems which provide cooled air are more commonly used and their operation can be complex, with a combination of cooling options with associated airflow rates and noise levels.

3.26 ADF suggests that to ensure good acoustic conditions, the noise levels within living rooms and bedrooms should not exceed LAeq,T 30 dB. It is included as additional commentary within the document and is not a mandatory requirement. This originates from the BS 8233:1999 [28] noise limits for noise ingress and the levels for living rooms are lower than those within CIBSE Guide A 2015 [29] and Sound Control for Homes [30]

guidance. A summary of the proposed noise levels from various guidance is shown in Table 3-4.

3.2.2 Approved Document F (ADF) Ventilation Condition

3.27 Recommendations for desirable internal ambient noise levels for ADF ventilation conditions are set out in Table 3-5.

Table 3-4 Indoor ambient noise levels from mechanical services – summary of guidance levels

Room Type

Approved Document F LAeq, dB

CIBSE Guide A 2015 – Table 1.5

Sound Control for Homes – BRE/CIRIA LAeq, dB

LAeq, dB

NR

Bedroom

30

30

25

30

Living Room

30

35

30

35

Dining Room

35

Bathroom / WC

45

Kitchen

45-50

40-45

45

 

Table 3-5 Indoor ambient noise levels from mechanical services – ADF ventilation conditions

Ventilation Condition

Possible system or design solution

Source for desirable internal ambient noise levels from mechanical services (with reference to Table 3-4)

ADF – Whole Dwelling Ventilation

System 3: Continuous mechanical extract (MEV), minimum low ventilation rates

System 4: Continuous mechanical supply and extract with heat recovery (MVHR), minimum low ventilation rates

Approved Document F

ADF – Extract Ventilation

System 1: Intermittent extract fans

System 3: Continuous mechanical extract (MEV), minimum high ventilation rates

System 4: Continuous mechanical supply and extract with heat recovery (MVHR), minimum high ventilation rates

Comfort criteria from CIBSE Guide A 2015, Table 1.5

or

Sound Control for Homes

ADF – Purge Ventilation

Manually controlled fan exchanging a minimum 4 air changes per hour

No desirable noise levels are currently proposed based on the lack of evidence of acceptable noise levels when providing purge ventilation for the purpose of rapidly diluting indoor pollutants.

 

3.2.3 Overheating Condition

3.28 The use of mechanical systems to control overheating could include systems which provide ambient air at high ventilation rates (ventilative cooling) or systems which provide cooled air, commonly referred to as comfort cooling systems.

3.29 These systems would normally be occupant controlled, but there may be options for automation.

3.30 Recommendations for desirable internal ambient noise levels for overheating conditions are set out in Table 3-6.

Table 3-6 Indoor ambient noise levels from mechanical services – Overheating condition

Possible system or design solution

Source for desirable internal ambient noise levels from mechanical services

(with reference to Table 3-4)

Ventilative cooling

or

Comfort cooling

Comfort criteria from CIBSE Guide A 2015, Table 1.5 with reference to section 1.10.10 of CIBSE Guide A

 

3.31 The desirable noise levels shown in Table 3-6 are based on systems which are operated to meet the design conditions to control overheating.

3.32 Section 1.10.10 of CIBSE Guide A 2015 states that the values its Table 1.5 are only a guide and that:

‘Higher or lower values may be appropriate based on economics, space use, user needs etc.’

3.33 It goes on to state that a range of +/- 5dB may be acceptable depending on the particular situation.

3.34 The duration, how frequent they occur, degree of occupant control and magnitude of the noise levels associated with the overheating condition should be taken into consideration when establishing suitable noise levels.

3.35 Higher noise levels, e.g. 5 or 10 dBA higher (refer to BS ISO 17772-1 [31] are likely to be acceptable in some operating scenarios, where rapid

changes to the cooling or ventilation rates quickly improve the thermal comfort of the occupant.

3.36 Equally, lower noise levels may be appropriate for some types of residential development.

3.37 Mechanical services noise levels not exceeding LAeq,T 24 dB within bedrooms may be required to prevent adverse reaction from occupants when falling asleep [27].

3.38 When considering variations to the proposed desirable levels, the classification system from Cost Action TU0901[32] and default design values from BS EN 15251[33] may be used as a guide.

4. Glossary

Acoustic terminology

Noise

Typically defined as unwanted, unpleasant or disturbing sound

Frequency (Hz)

The number of oscillations in acoustic pressure per second. It represents the ‘tone’ of the sound. Often determined in octave bands (where the upper limit of the band is twice the frequency of the lower limit) or one-third octave bands (where the upper limit is the lower limit time the cube root of two)

Maximum sound pressure level (Lmax)

The maximum or highest sound pressure level measured either over 1/8th of a second (‘fast’ time weighting, LFmax), or over a whole second (‘slow’ time weighting, LSmax)

Equivalent continuous sound pressure level (Leq,T)

The average of the total sound energy over a specified time period (T). Leq represents the equivalent sound level that a fluctuating source would have compared to a steady source with the same total sound energy over a specific time period. Commonly used as a descriptor of human perception of sound over time.

‘A’ weighting

Frequency-dependent weighting based on the response of the human auditory system which has been found to correlate well with the subjective response to sound. Denoted by the use of the letter ‘A’. For example, dBA denotes an ‘A’ weighted sound level in decibels, or LAmax denotes an ‘A’ weighted maximum sound pressure level.

Internal Ambient Noise Level (IANL)

The noise level within a room or enclosed space. Usually determined as an equivalent continuous sound pressure level over a specific time period (LAeq,T, dB)

Noise Rating (NR) curve

A single figure term used to reflect the spectral frequency content of noise. Although originally proposed to assess environmental noise, NR curves are now typically used to describe noise from mechanical ventilation systems in buildings.

Lnight,outside

The incident external A-weighted long-term average sound level as defined in ISO 1996-2: 1987, determined over all the night periods of a year, in which the night is eight hours between 23:00 and 07:00.

 

Other terms

AVO

Acoustics, Ventilation, Overheating (e.g. AVO Guide, AVO Group).

Overheating condition

The situation where measures are in place to mitigate overheating to meet agreed compliance criteria.

Dynamic thermal modelling

A technique that can be used to simulate internal temperatures in dwellings before they are built

Heat recovery

The process of using warm air extracted from the room to heat incoming colder air before it is supplied to the room, thereby reducing the ventilation heat-losses.

Ventilative cooling

Cooling by means of introducing external ambient temperature air at a high ventilation rate. Can be either passive (no fans) or mechanical (with fans).

Purge ventilation

Ventilation to aid removal of high concentrations of pollutants and water vapour released from occasional activities such as painting and decorating or accidental releases such as smoke from burnt food or spillage of water.

Comfort cooling

Cooling by means of a refrigerant cycle. This would include ‘air conditioning’ systems and the use of fan coil units (FCUs).

MEV

Mechanical extract ventilation.

MVHR

Mechanical ventilation with heat recovery.

Appendix A – additional information

A.1 This appendix provides additional information on ventilation and overheating to help provide further context to the guidance in Section 2 of this document. This is not an exhaustive list of relevant information but does signpost a number of the documents referred to during the production of this guide.

A.1 Ventilation

A.2 Ventilation requirements for dwellings (and other buildings) are covered under the Building Regulations and set out within ADF, which requires that:

‘There shall be adequate means of ventilation provided for people in the building.’

A.3 The document then goes on to state that:

‘Ventilation is simply the removal of ‘stale’ indoor air from a building and its replacement with ‘fresh’ outside air.

Ventilation is required for one or more of the following purposes:

a) Provision of outside air for breathing;

b) Dilution and removal of airborne pollutants, including odours;

c) Control of excess humidity (arising from water vapour in the indoor air);

d) Provision of air for fuel-burning appliances (which is covered under Part J of the Building Regulations)

Ventilation may also provide a means to control thermal comfort but this is not controlled under the Building Regulations. Part L addresses minimising energy use due to the effects of solar gain in summer.’

A.4 ADF describes three types of ventilation provision and associated ventilation rates. These are summarised in Table 2-1 of this guide.

A.5 In addition to the above ADF also states:

‘Purge ventilation provisions may also be used to improve thermal comfort, although this is not controlled under the Building Regulations.’

A.6 Section 5 of ADF provides details of four template ‘Systems’ which comply with the above strategy

for new dwellings and can be adopted to demonstrate compliance.

A.7 Each of these ‘Systems’ demonstrates adequate ventilation provision, the details of each system are summarised in Table 2-2 of this guide.

A.8 With reference to the design of ventilation systems 1 and 2, ADF states the following:

‘The background ventilators have been sized for the winter period. Additional ventilation may be required during warmer months and it has been assumed that the provisions for purge ventilation (e.g. openable windows) could be used.’

A.9 The document also provides similar advice with respect to the sizing of systems 3 and 4.

A.10 With regard to the provision of purge ventilation within habitable rooms, the approved document provides the following note.

‘There may be practical difficulties in achieving this (e.g. if unable to open a window due to excessive noise from outside.’

A.11 No objective guidance is provided in the Approved Document as to what constitutes an ‘excessive’ level of noise.

A.12 Figure A-1 illustrates the principles of the most commonly used ventilation systems described in Table 2-2 (i.e. systems 1, 2, 3 and 4).

A.13 Notwithstanding the above information, it is important to note that the ventilation requirements contained in ADF are a minimum standard only.

Figure A-1 Illustrations of ADF ventilation systems from top left to bottom right (System 1, System 2, System 3, System 4)

A.2 Thermal Comfort and Overheating

A.14 ISO 7730 [34] describes thermal comfort as:

‘that condition of body and mind which expresses satisfaction with the thermal environment.’

A.15 Part of providing thermal comfort in a residential building is avoiding ‘overheating’. In the Zero Carbon Hub discussion paper ‘Next Steps in Defining Overheating’ [4] (‘ZCH’) the following definition of overheating in dwellings is provided:

‘In a general sense, by overheating we mean the phenomenon of excessive or prolonged high temperatures in homes, resulting from internal or external heat gains, which may have adverse effects on the comfort, health or productivity of the occupants.’

A.16 In CIBSE Technical Memorandum 52 [35] (‘TM52’), the following is stated in relation to overheating:

‘Overheating is a widely used term but it is not precisely defined or understood. It implies that building occupants feel uncomfortably hot and that discomfort is caused by the indoor environment. Generally this is taken to mean that the temperature in the building is too high for comfort. This is the approach usually used in predicting the danger of overheating. In fact there are a number of other factors that are important, both environmental (such as humidity and air movement) and contextual (such as the purpose of the building, its design and management, and the occupants’ attitude to it), which will also be important.’

A.2.1 Building Regulations

A.17 There are no specific requirements relating to overheating in residential dwellings as part of the UK Building Regulations. Both ADF (see above) and Part L1A of The Building Regulations briefly mention overheating but do not provide detail on what constitutes overheating. In the section on ‘buildings other than dwellings’ ADF refers to Part L2A of the Building Regulations for guidance, however this guidance is related to limiting solar gains rather than avoiding overheating.

A.18 Approved Document L1A [36] provides guidance on limiting the effects of heat gains in summer although no objective performance standards are identified. However, reference is provided to the SAP 2012 Appendix P assessment methodology and this document includes a simplified test for

overheating risk (this is discussed in more detail below).

A.2.2 The London Plan [37]– Policy 5.9 Overheating and Cooling

A.19 Policy 5.9 of the London Plan 2017 specifically mentions overheating and states the following:

‘The Mayor seeks to reduce the impact of the urban heat island effect in London and encourages the design of places and spaces to avoid overheating and excessive heat generation, and to reduce overheating due to the impacts of climate change and the urban heat island effect on an area wide basis.’

A.20 In relation to planning decisions the policy states that:

‘Major development proposals should reduce potential overheating and reliance on air conditioning systems and demonstrate this in accordance with the following cooling hierarchy:

  1. minimise internal heat generation through energy efficient design
  2. reduce the amount of heat entering a building in summer through orientation, shading, albedo, fenestration, insulation and green roofs and walls
  3. manage the heat within the building through exposed internal thermal mass and high ceilings
  4. passive ventilation
  5. mechanical ventilation
  6. active cooling systems (ensuring they are the lowest carbon options).

Major development proposals should demonstrate how the design, materials, construction and operation of the development would minimise overheating and also meet its cooling needs. New development in London should also be designed to avoid the need for energy intensive air conditioning systems as much as possible. Further details and guidance regarding overheating and cooling are outlined in the London Climate Change Adaptation Strategy.’

A.21 In relation to Local Development Framework (LDF) preparation the policy also states:

‘Within LDFs boroughs should develop more detailed policies and proposals to support the avoidance of overheating and to support the cooling hierarchy.’

A.2.3 Overheating Criteria and Guidance

A.22 Until the release of TM59 there was no universally accepted definition of what constitutes overheating in residential dwellings. Previously, building services engineers used two main methods of identifying if overheating was likely to occur. The two methods are summarised in Table A-1.

Table A-1 Overheating Criteria

Deterministic Thermal Comfort Models [Note 1]

Adaptive Thermal Comfort Models [Note 2]

Provides absolute criteria (temperatures and durations) for where overheating is likely to occur in residential buildings (living rooms and bedrooms)

Provides criteria to assess the risk of overheating based on adaptive comfort (this takes into account that people acclimatise to extended periods of hot weather)

Note 1 – described in ISO 7730, BS EN 15251, CIBSE TM36 [38] and CIBSE Guide A 2006 [39]

Note 2 – described in CIBSE Guide A 2015 and CIBSE TM52

A.23 However, TM59 now describes specific criteria for overheating in dwellings based on both the deterministic and adaptive models above.

CIBSE Technical Memorandum 59 ‘Design methodology for the assessment of overheating risk in homes’

A.24 CIBSE TM59 provides guidance on the assessment of overheating in dwellings (including care homes and student accommodation). The document sets out a standardised methodology for predicting temperatures inside dwellings (using dynamic thermal modelling) and also provides overheating ‘compliance criteria’.

A.25 CIBSE TM59 notes that:

This methodology is proposed for all residences and should especially be considered for:

— large developments

— developments in urban areas, particularly in southern England

— blocks of flats

— dwellings with high levels of insulation and air-tightness

— single aspect flats.

Individual houses and developments with a low risk of overheating may not require the use of dynamic thermal modelling…

A.26 Separate compliance criteria are provided for dwellings that are ‘predominantly naturally ventilated’ and dwellings that are ‘predominantly mechanically ventilated’. In relation to the different methods of ventilation TM59 states the following:

‘Homes that are predominantly naturally ventilated, including homes that have mechanical ventilation with heat recovery (MVHR), with good opportunities for natural ventilation in the summer should assess overheating using the adaptive method based on CIBSE TM52 (2013)

In order to allow the occupants to ‘adapt’, each habitable room needs operable windows with a minimum free area that satisfies the purge ventilation criteria set in Part F of the Building Regulations for England (NBS, 2010), and equivalent regulations in other countries, i.e. the window opening area should be at least 1/20th of the floor area of the room (different conditions exist for windows with restricted openings, and the same requirement applies for external doors). Control of overheating may require accessible, secure, quiet ventilation with a significant openable area.

Homes that are predominantly mechanically ventilated because they have either no opportunity or extremely limited opportunities for opening windows (e.g. due to noise levels or air quality) should be assessed for overheating using the fixed temperature method.’

A.27 The compliance criteria for each ventilation type, taken directly from TM59 are detailed below.

A.28 Compliance criteria for predominantly naturally ventilated homes:

‘Compliance is based on passing both of the following two criteria:

a) For living rooms, kitchens and bathrooms: the number of hours during which ΔT is greater than or equal to one degree (K) during the period May to September inclusive shall not be more than 3 per cent of occupied hours (CIBSE TM52 Criterion 1: Hours of exceedance).

b) For bedrooms only: to guarantee comfort during the sleeping hours the operative temperature in the bedroom from 10 pm to 7 am shall not exceed 26 °C for more than 1% of annual hours. (Note: 1% of the annual hours between 22:00 and 07:00 °C will be recorded as a fail.)

Criteria 2 and 3 of CIBSE TM52 may fail to be met, but both a) and b) above must be passed for all relevant rooms.’

A.29 Compliance criteria for predominantly mechanically ventilated homes:

‘For homes with restricted window openings, the CIBSE fixed temperature test must be followed, i.e. all occupied rooms should not exceed an operative temperature of 26 ˚C for more than 3% of the annual occupied annual hours (CIBSE Guide A (2015a)).’

A.30 In addition to the compliance criteria above TM59 provides further information on adjustments for homes with vulnerable occupants and ‘non-mandatory’ criteria for temperatures in corridor areas.

A.31 TM59 refers to the adaptive thermal comfort criteria in CIBSE Technical Memorandum 52 (TM52) and these are described in more detail in the following paragraphs.

A.32 TM52 outlines three overheating design criteria. These are all defined in terms of ΔT, the difference between the actual operative temperature in the room at any time (Top) and the limiting maximum acceptable temperature (Tmax). ΔT is calculated as:

ΔT = Top –Tmax (K)

A.33 ΔT is rounded to the nearest degree (i.e. for ΔT between 0.5 and 1.5 the value used is 1K, for 1.5 to 2.5 the value used is 2K and so on).

A.34 Criteria 1 – Hours of Exceedance (He): The number of hours (He) that ΔT is greater than or equal to one degree (K) during the period May to September inclusive shall not be more than 3% of occupied hours.

A.35 How often a building/zone exceeds its comfort range during the summer months (May-September) is a useful indicator of its thermal characteristics and potential risk of overheating.

A.36 Criteria 2 – Daily Weighted Exceedance (We): To allow for the severity of overheating the Daily Weighted Exceedance (We) shall be less than or equal to 6 in any one day.

A.37 The value of 6 is an initial assessment of what constitutes an acceptable limit of overheating on any single day.

A.38 Criteria 3 – Upper Limit Temperature (Tupp):

A.39 To set an absolute maximum value for the indoor operative temperature the value of ΔT shall not exceed 4K.

A.40 This criterion covers the extremes of hot weather conditions and future climate scenarios.

Standard Assessment Procedure for Energy Rating of Dwellings’ (SAP), 2012

A.41 Appendix P of ‘The Government’s Standard Assessment Procedure for Energy Rating of Dwellings’ [40] (‘SAP’), 2012 provides a method for assessing the energy performance of dwellings and as part of this provides an ‘Assessment of internal temperature in summer’ (the document does note that this assessment is not integral to SAP and does not affect the calculated SAP ratings).

A.42 The SAP Appendix P assessment predicts a likelihood of high internal temperature during hot weather that varies from ‘not significant’ to ‘high’. However, it should be noted that this method is a relatively simple tick box type assessment that only considers a few basic variables as it is focussed on assessing the energy efficiency of a dwelling and not thermal comfort or health impacts etc.

Housing Health and Safety Rating System

A.43 The Housing Health and Safety Rating System [41] (‘HHSRS’) is a ‘risk-based evaluation tool to help local authorities identify and protect against potential risks and hazards to health and safety from any deficiencies identified in dwellings’.

A.44 In Section 3 of the HHSRS document ‘Guidance for landlords and property related professionals’, the following is stated in relation to the effects on health as temperatures rise:

‘increase in thermal stress, increase in cardio vascular strain and trauma, and increase in strokes. Mortality increases in temperatures over 25°C. Although not common, problems can occur in the UK.’

A.45 In addition to the above, in the HHSRS ‘Operating Guidance’ document, further information in relation to overheating and noise is provided in paragraph 3.17:

‘There should be means for cooling during hot summer weather, either by natural ventilation or by air conditioning. The means should be controllable, properly installed and maintained, and appropriate, having regard to the particular part of the dwelling. While openable windows can provide ventilation, occupiers may be reluctant to use them for security reasons, or because of external noise levels, especially at night.’

Zero Carbon Hub Guidance

A.46 The Zero Carbon Hub has produced a number of documents on the subject of overheating. In ZCH recommendations are made for defining overheating in new dwellings and assessing the potential for these buildings to overheat in future.

A.47 The paper recommends an initial approach for risk assessing and defining overheating and the ZCH propose that their recommendations be adopted in principle by the relevant government departments as national policy.

IEA Energy in Buildings and Communities Programme – Annex 62 – Ventilative Cooling

A.48 The International Energy Agency (IEA) Energy in Buildings and Community (EBC) Programme [42] carries out research and development activities towards near zero energy and carbon emissions.

A.49 Annex 62 of the Programme looks at ‘ventilative cooling’ and provides the following definition of the term ‘ventilative cooling’:

‘The application of ventilation air flow to reduce the cooling loads in buildings’

A.50 To help address cooling challenges in buildings, Annex 62 focuses on the following:

  • ‘Development of design methods and compliance tools related to predicting, evaluating and eliminating the cooling need and the risk of overheating in buildings, and
  • To develop new attractive energy efficient ventilative cooling solutions.’

Dynamic Thermal Modelling

A.51 Dynamic thermal modelling is a technique that can be used to simulate internal temperatures in dwellings before they are built. This enable engineers to identify if and how often rooms in dwellings are likely to ‘overheat’.

A.52 Building services engineers generally use thermal analysis software to undertake dynamic thermal modelling.

A.53 In order to model temperatures inside dwellings a large amount of information is required, including the following:

  • Site location and building orientation
  • Weather files for the site
  • Details of elevational treatments (areas, insulation performance and solar transmittance etc.)
  • Thermal mass properties
  • Details of opening doors and windows (size, shape, opening type)
  • Details of any mechanical ventilation and / or heat recovery systems
  • Internal and external shading
  • Room types and information
  • Occupancy profiles (occupied hours, resident’s activities etc.)
  • Details of internal thermal gains (lighting, equipment, pipework etc.)

A.54 Before the release of TM59, the results of dynamic thermal modelling assessments were highly dependent upon assumptions made by the engineer undertaking the analysis, particularly in relation to occupancy profiles.

A.55 However, the CIBSE TM59 document now provides a standardised approach to predicting overheating using dynamic thermal analysis. The methodology is necessarily prescriptive to enable it to be consistently applied and it also includes clear reporting requirements to enable all stakeholders to understand the assumptions made, review the conclusions and understand the likely design implications.

A.56 Modellers should be asked to provide the information described in Table A-2 from the dynamic thermal model.

Table A-2 Information required from thermal model

Information required from dynamic thermal model in order to undertake the acoustic assessment

The area of opening assumed

The number of hours on which open windows are required to mitigate overheating within the daytime (07:00 – 23:00) and separately, night time (23:00 – 07:00) periods.

Appendix B – application of this guide

B.1 Introduction – observing internal noise level guidelines

B.1 This appendix offers an overview of the typical design process, and provides a worked example to illustrate the steps that may be appropriate.

B.2 Approach to assessment & preparing advice – key steps

B.2 Note that the suggested process in this section assumes that the site layout including building orientation has already been optimised following a process of good acoustic design, as has the space planning within the building.

B.3 There are three key steps in the process of considering the effect that noise can have in relation to design strategies for ventilation and mitigating overheating and these are highlighted in Table B-1 and illustrated in Figure B-1.

Table B-1 Three steps to link the noise to the ventilation and overheating strategies

Step

Activity

Output advice

1

Quantify external noise levels

Determine external noise levels impacting on proposed living rooms and bedrooms.

Report the following values and describe the method by which they have been determined.

 Daytime (LAeq,16h)

 Night time (LAeq,8h)

 Night time maximum (LAFmax) levels and regularity of occurrence.

2

Assess noise & ventilation

Consider the effect of potential ventilation strategies on the acoustic conditions in living rooms and bedrooms.

Refer to Table 3-1 for indoor ambient noise level guidelines from external sources, and Table 3-5 for mechanical services noise associated with ventilation provision.

The facade sound insulation assessment should include details of the proposed or feasible ventilation strategies, along with other facade details such as glazing performance

3

Assess noise & overheating

Rooms may be grouped by Low, Medium and High risk categories according to Tables 3-2 and 3-3.

Consider noise from mechanical systems associated with controlling overheating.

It may be appropriate to carry out an overheating assessment regardless of the association with the noise impact on the proposed development. Risk factors for overheating are listed in CIBSE TM59, although other methods of carrying out an overheating assessment may also be suitable.

Refer to Table 3-6 for mechanical services noise associated with controlling overheating.

Follow procedure in Figure 3-1 for noise from external sources.

Low risk category rooms according to Level 1 assessment

A “Level 1” assessment may be sufficient. It is unlikely that external noise ingress will be problematic if using opening windows to mitigate overheating, although it may be appropriate to demonstrate this with suitable calculations.

Medium risk category rooms according to Level 1 assessment

It would be prudent to carry out more detailed analysis for rooms in this category, because if open windows are required for extended periods to mitigate overheating the noise impact may be significant. Properties at the lower end of this noise category are at less risk, and hence occupants may tolerate a longer duration of exposure to the noise than at the higher end of this category.

It may be appropriate to consider the generic overheating risk factors for the proposed development [refer to Appendix A, paragraph A.25] along with the noise levels in order to take a balanced view of the level of formal assessment that is suitable.

High risk category rooms according to Level 1 assessment

A ‘Level 2’ assessment is normally appropriate in accordance with Table 3-3. For rooms in this noise exposure category, an integrated approach should consider the overheating strategy along with external noise ingress. The potential adverse acoustic impact during the overheating mitigation should be assessed for potential suitability.

 

Figure B-1 Typical activity of the acoustic designer in developing the design

B.3 Beginning Step 2: consider noise effects of ventilation strategy

B.4 Noise considerations associated with ventilation strategies described in AD-F are summarised in

Table B-2. It is noted that there is no obligation to adopt one of these template systems from AD-F; other systems may be considered by reference to the similar system described, subject to satisfaction of the Building Control officer.

Table B-2 Summary of potential noise issues associated with ventilation strategies described in ADF

ADF System

External noise ingress considerations

Mechanical system noise considerations

Approximate guideline external noise limits. [Note 1]

1

In the winter period, noise ingress is likely to be defined by the performance of the background ventilators (trickle vents), windows and other façade elements.

However, this ADF system relies on additional ventilation outside the winter period to control excess humidity.

Hence this system is only appropriate if this additional ventilation can be provided whilst maintaining acceptable internal noise conditions. This will normally be addressed by undertaking the assessment of noise and overheating (see Step 3) because the means of mitigating overheating will also provide a means of controlling excess humidity outside the winter period.

Intermittent kitchen and bathroom fans should have suitable noise levels.

When using typical opening windows:

~ LAeq,16h 58 dB day

~ LAeq,8h 53 dB night

 (Assess Lmax also)

2

As for System 1

None – no mechanical components

As for System 1

3

Noise ingress is likely to be defined by the performance of the background ventilators (trickle vents), windows and other façade elements.

ADF advises that

‘controllable background ventilators having a minimum equivalent area of 2,500 mm2 should be fitted in each room, except wet rooms….’

May be a centralised or decentralised MEV system.

For a centralised system, the location of the fan is important for structure-borne and airborne noise. System noise may affect living rooms and bedrooms as well as the rooms in which the extract inlets are located i.e. wet rooms.

For a decentralised system, there are individual fans extracting from each bathroom, toilet, kitchen and utility room. The noise effects on adjacent living rooms and bedrooms should be considered. [Note 2]

With standard double glazing and trickle vent:

~LAeq,16h 58 dB day

~LAeq,8h 53 dB night

 (Assess Lmax also)

With high performing acoustic glazing and an ‘acoustic’ trickle vent:

~ LAeq,16h 68 dB day

~ LAeq,8h 63 dB night

 (Assess Lmax also)

4

No trickle vents required. Consider noise ingress through other facade elements.

MVHR is a centralised system ducted to supply outlets in living rooms and bedrooms as well as to extracts in wet rooms.

The unit location is important for structure-borne and airborne noise.

Consider ducted noise, particularly to bedrooms. Consider also cross-talk sound transmission via ducts. [Note 2]

With standard double glazing and no trickle vent:

~ LAeq,16h 67 dB day

~ LAeq,8h 57 dB night

 (Assess Lmax also)

With high performing acoustic glazing:

~ LAeq,16h 73 dB day

~ LAeq,8h 68 dB night

 (Assess Lmax also)

N.B. With secondary glazing higher sound insulation may be achieved.

Note 1 – Refer to Sections B.3.1, B.3.2 and B.3.3 for the basis of calculated noise levels

Note 2 – Hybrid ventilation strategies may involve mechanical supply and/or extract to specific habitable rooms, in which case those sources of noise should be considered.

B.5 To determine approximate guideline external noise levels it is necessary to make a number of assumptions regarding the spectrum of external noise, geometry of the facade and room, and element performances, using the detailed method described in BS 8233. The calculated level differences are summarised in Table B-3 and used to estimate the approximate guideline values indicated in Table B-2.

B.3.1 Potential facade elements and their associated performance

B.6 It is assumed for the sample calculations below that external noise ingress through the glazing and any vent is the most significant route, and the noise ingress through other facade elements is not significant by comparison. While this is likely to be a reasonable assumption for the lower end of the sound insulation performances sought, towards the higher end attention must also be given to other facade elements.

B.7 The calculations here assume double glazing; the sound insulation of triple glazing is not generally much better than that of double glazing. The sealing of any opening elements may be the limiting factor when trying to achieve higher levels of sound insulation, particularly the sealing of sliding doors, for example. Any performance considered for glazing should include the frame and seals for opening elements.

B.3.2 Calculated external noise levels: Systems 1 & 2

B.8 It is noted that the trickle vent areas indicated in ADF are based on calculated air flow rates for the winter condition, and that the provisions for purge ventilation (i.e. opening windows) may be used at other times of the year.

B.9 It is not clear what area of opening is required at other times of the year to achieve whole dwelling ventilation rates described in ADF. While more extensive window opening may be required to control thermal comfort, it is assumed that the minimum window opening described as “ajar” is sufficient for achieving whole dwelling ventilation rates outside of winter months.

B.10 The research presented in Table 4-3 of NANR116 [43] on different window types open different amounts indicates that for a window ajar, the value of Dw is not less than 20 dB, where

Dw is the weighted level difference between external levels at 2m and internal levels. The difference between Dw and Dw+Ctr is indicated to be around 2 dB for an open window, hence a minimum level difference of 18 dB is assumed for a non-specific type of window that is ajar. Note that this does not offer sufficient open area to mitigate overheating, but only sufficient open area to achieve ADF whole dwelling ventilation rates.

B.11 Assuming that internal levels should remain within the ‘low’ risk category defined by Table 3-3 of this document, and adding 18 dB to the values for bedrooms and living rooms yields the values indicated in Table B-2.

B.3.3 Calculated external noise levels: System 3

B.12 External levels for use of AD-F System 3 are based on calculations according to the detailed method described in BS 8233, (equivalent to the method in BS EN 12354-3) [44]. A typical small bedroom is considered. The Technical housing standards – nationally described space standard [45] indicates that a single bedroom should be at least 7.5 m2. The glazed area is considered to 25% of the floor area, as described in SAP.

B.13 These dimensions represent unfavourable ratios between element performance and overall facade level difference, but worse case conditions may be found in practice. On the basis of these assumptions, the relation between element performance and partial internal level (L2,route) due to each noise ingress path reduces to the following relationship:

  • L2, glass = L1,ff – (Rw+Ctr) – 2
  • L2, vent = L1, ff – (Dn,e,w+Ctr) + 5.

B.14 Where the total internal level is the logarithmic sum of the partial level due to ingress through the glass, L2, glass, and ingress through the vent, L2, vent, assuming that these routes dominate over other ingress transmission routes as noted above.

B.15 It is further assumed that the continuous equivalent external sound field is well approximated by the general road traffic noise spectrum described in BS EN 1793-3 [46] and therefore attenuation is well described by the (Rw+Ctr) parameter. The following assumptions are made regarding potential glazing and trickle vent performance:

  • Standard domestic double glazing with Rw (Ctr) 29 (-4) dB, from BS EN 12758 [47].
  • High acoustic performance windows with Rw (Ctr) 43 (-6) dB, from proprietary manufacturer’s data. Note that the details of the frame and sealing arrangements are important to maintain this performance for the whole window system.
  • Standard trickle vent, approx 2500 – 4000 mm2 effective area, Dn,e,w (Ctr) 31 (0) dB, typical proprietary manufacturer’s data.
  • High acoustic performance trickle vent, approx 2500 mm2 effective area, Dn,e,w (Ctr) 44 (-3) dB from proprietary manufacturer’s data.

B.3.4 Calculated external noise levels: System 4

B.16 The guideline values for AD-F System 4 are calculated on the same basis as for AD-F System 3, omitting the trickle vent. Note especially the comment regarding the performance of the frame for the glass, sealing arrangements and other facade elements where a higher overall sound insulation performance is sought.

Table B-3 Potential level differences for average Leq noise associated with different ventilation strategies

System

Typical windows and vent

High acoustic performance windows and vent

1, 2 (window ajar)

18 dB

18 dB

3 (with trickle vent)

23 dB

33 dB

4 (no trickle vent)

27 dB

38 dB

 

B.3.5 LAmax assessment

An assessment of the potential impact on sleep during the night time should always be undertaken. There is a growing consensus that exceeding the value of LAFmax 45 dB by up to 10 dB on up to 10 or 15 occasions during the night on a regular basis represents a LOAEL. Higher values may be acceptable for limited periods of the year, depending on the level and frequency of events. Refer to ProPG Appendix A for information on assessing individual noise events.

B.4 Beginning Step 3: consider noise effects of overheating mitigation strategy

B.17 It is recommended that the first step is for the acoustician to review and understand the strategy that is being proposed for meeting overheating design criteria. The strategy will normally consist of limiting heat gains (e.g. solar gains) and providing a means of cooling. The means of cooling may be provided by one of the methods described in Table B-4, or by other means. Appropriate noise levels for each type of cooling strategy should also take account of how often the means of cooling needs to be employed and for what duration. See Section 3 for the detail of the assessment of overheating and noise level guidance.

B.18 It may be helpful for the acoustician to produce a mark-up indicating the Level 1 assessment risk category for each façade in accordance with guidance in Table 3-2. This will allow the other members of the design team (especially those involved in the assessment of overheating) to understand locations in which the use of opening windows to mitigate overheating may not be appropriate.

B.19 It may be possible to reduce the noise impact by further reducing the heat gains, and hence reducing the regularity and/or duration for which the means of cooling needs to be employed. The London Plan overheating policy provides a useful reference as to the various mitigation options and their preferred hierarchy (refer to paragraph A.20).

B.20 For example, by reducing the extent of external glazing, by improving solar shading or using exposed thermal mass, the amount of cooling that is required to meet overheating criteria may be reduced. This will likely reduce either the magnitude or duration of any noise impact associated with the cooling provision.

B.21 Clearly, it is not the role of the acoustic practitioner to advise on the strategy for mitigating overheating. However, where relevant, the acoustic practitioner is encouraged to communicate to the design team and developer any acoustic benefit of reducing heat gains.

B.22 Ceiling mounted fans do not reduce the ambient temperature but can be used to increase air-movement in the room, and thus improve thermal comfort at hotter temperatures. If used, noise from ceiling mounted fans should be considered in the assessment.

Table B-4 Summary of potential noise issues associated with cooling strategy

Means of cooling

Description

External noise ingress considerations

Mechanical system noise considerations

Passive ventilative cooling

The room is ventilated at a higher rate than AD-F whole dwelling rate using external, ambient temperature air.

The ventilation is provided passively with no use of mechanical fans.

Passive ventilation may not be effective for single-sided dwellings; typically cross-ventilation is required with reference to IEA Annexe 62 on ventilative cooling [41].

A level difference of around 12 dB from external free-field levels to reverberant internal levels can typically be assumed for a window that is sufficiently open to enable ventilative cooling although this should be reviewed for the specific project (refer to Section 3.1.3).

Will require significant openings in the façade. Ingress of external noise via these openings will need to be considered.

Where opening windows result in unacceptably high internal levels, solutions providing enhanced sound insulation can be considered – refer to table B-12.

N/A (unless ceiling fans used)

Mechanical ventilative cooling

The room is ventilated at a higher rate than AD-F whole dwelling rate using external, ambient temperature air.

The ventilation is mechanically driven using fans.

This may either be an independent system or a boost mode for the MVHR system that is also used to provide the AD-F whole dwelling ventilation.

Duct attenuators are very likely to be necessary to address fan noise.

These are likely to be sufficient to attenuate external noise ingress via the ducts.

If intake and/or exhaust ducts penetrate the facade locally, the effect on sound insulation should be reviewed.

Air-flow rates will be significantly higher than those required for AD-F whole dwelling ventilation. Fan noise will therefore be higher and duct-borne, breakout and structure-borne paths must be appropriately considered.

Airflow (regenerated) noise will also need to be considered at grilles.

Mechanically cooled air

The room is provided with air that has been mechanically cooled using a refrigeration cycle. May involve air being recirculated from the room. Commonly referred to as mechanical cooling, air-conditioning or comfort cooling.

None – no air-path to outside.

Indoor units (fan-coils, cassettes etc.) include a fan and require significant air-flow rates to convey cooling to the room. Both the fan and the airflow are sources of noise and must be appropriately addressed. Cooling can also be provided via an MVHR system. This may affect fan pressure and flow rates and therefore noise levels.

Outdoor units (which reject heat to the atmosphere) also generate noise and this may have an impact on nearby external amenity spaces or result in break-in to nearby dwellings.

Chilled beams/ radiant cooling

(Note that this is rarely used in residential)

A cooled surface or finned-tube heat exchanger is used to cool the air within the room. The cooling is provided by water that has been cooled using either a refrigeration cycle or by ground-source cooling. The ventilation is either passive or, in the case of active chilled beams, uses fans.

None – no air-path to outside.

Water flow may generate some noise. In the case of active chilled beams, fan noise and air-flow noise must also be considered.

 

B.5 Information that may be appropriate or required to accompany a planning submission

B.23 Table B-5 lists information that may be appropriate or required by the Local Planning

B.24 Authority (LPA) to provide with a planning application. Individual circumstances of the project and the requirements of the LPA can vary.

Table B-5 Information that it may be appropriate to provide with the planning application

Planning stage

Noise impact

Noise implications for ventilation strategy

Noise implications for overheating strategy

Outline application

Details of environmental noise impact across the site.

Potential effect of mitigation such as barriers, or use of buildings following good acoustic design to reduce noise impact on outdoor amenity areas and facades of habitable rooms.

Feasibility of ventilation strategies across the site with the noise levels measured and with any potential mitigation.

Feasibility of potential overheating strategies with the noise levels measured and with any potential mitigation.

Suggest a schedule of testing is developed for a proportion of dwellings at detailed design stage.

Testing to include both external noise ingress and any mechanical systems in accordance with ANC Good Practice Guide on Measurement of Noise levels in buildings.

Detailed application

Details of anticipated noise levels at an appropriate selection of residential properties.

Calculations demonstrating that the internal noise levels from external sources are consistent with the levels in Table 3-1, with justification where there are exceedances.

Specifications for noise levels from mechanical ventilation systems.

Consider a schedule of testing for both external noise ingress and any mechanical ventilation provision in accordance with ANC Good Practice Guide on Measurement of Noise levels in buildings.

Calculations demonstrating that the internal noise levels from external sources are consistent with the guideline levels in Table 3-3, with justification where there are exceedances.

Specifications for noise levels from mechanical cooling systems.

Consider a schedule of testing for both external noise ingress and any mechanical systems in accordance with ANC Good Practice Guide on Measurement of Noise levels in buildings.[Note 1]

Note 1 – Where the development is subject to EIA Regulations, a reference to compliance testing should be included within the monitoring commitments.

B.6 Worked example

B.6.1 Step 1: External noise levels impacting on the proposed development

B.25 The external free-field noise levels at each of the four receptor locations are described in Table B-6. Four notional receptor locations correspond to the rooms, dwelling or groups of dwellings that are being assessed.

B.26 The noise levels have been determined by means of a combination of site noise survey and noise-mapping. It may be appropriate to give further details of the method by which levels have been determined and include an estimate of uncertainty in the values.

Table B-6 Consider noise levels at four different receptors across the example site

External free-field noise level

Receptor A

Receptor B

Receptor C

Receptor D

Daytime LAeq,16h , dB

52

58

64

72

Night-time LAeq,8h , dB

44

51

59

67

Night-time LAFmax , dB and frequency of occurrence

Consideration should also be given to Lmax levels. For brevity, this part of the assessment is omitted from this worked example. Refer to ProPG Appendix A

 

B.6.2 Step 2 assessment

B.27 In all cases below, an assessment or specifications for noise from mechanical systems for ventilation should be carried out in accordance with Table 3-5.

Table B-7 Worked example of Step 2 assessment – considering the effect of potential ventilation strategies on the acoustic conditions

Receptor

External free-field noise levels

Proposed solution

A

Daytime LAeq,16h 52 dB

Night-time LAeq,8h 44 dB

AD-F System 1

See notes in Table B-2.

No further calculations provided.

B

Daytime LAeq,16h 58 dB

Night-time LAeq,8h 51 dB

AD-F System 3

(noting that System 1 may be feasible)

(Detailed calculations available on request)

C

Daytime LAeq,16h 64 dB

Night-time LAeq,8h 59 dB

AD-F System 1 with attenuated solution for higher ventilation rate (refer to Table B-10).

The attenuated passive acoustic vents enable the higher ventilation rates to be achieved outside the winter period without using partially open windows.

(Detailed calculations available on request)

D

Daytime LAeq,16h 72 dB

Night-time LAeq,8h 67 dB

AD-F System 4

(Detailed calculations available on request)

 

B.6.3 Step 3 assessment

B.28 Those receptors that are considered “low risk” from the Level 1 assessment according to Table 3-2 do not require any further qualification of the overheating strategy to inform the acoustic strategy (although it may be required by the mechanical engineer to inform the overheating design).

B.29 For the receptors that are considered “medium” or “high risk” from the Level 1 assessment according to Table 3-2, a detailed overheating assessment has been carried out in accordance with CIBSE TM59. This demonstrates that on the north eastern elevations, open windows are required infrequently (e.g. on up to six days of the year during the daytime and four occasions during the night time, for limited durations). On the south-western elevations, opening windows are required frequently (e.g. up to 34 occasions during the day, and 27 occasions at night, for extended durations).

B.30 Worked examples of Step 3 assessments for each receptor are set out in Table B-8 to B-11.

Table B-8 Worked example of Step 3 assessment – considering the effect of potential overheating mitigation strategies on the acoustic conditions – Receptor A

External free-field noise level (dB)

Level 1 risk assessment (in line with Table 3-2)

Notes on overheating mitigation and requirement for Level 2 risk assessment

Level 2 risk assessment (in line with Table 3-3, with mitigation)

Daytime LAeq,16h 52

Night-time LAeq,8h 44

Low

The low risk category according to the Level 1 assessment indicates that internal levels are expected to achieve BS 8233 reasonable conditions if overheating control is provided by means of partially open windows.

When windows are partially open, there is a low risk of adverse effects; no further noise assessment is proposed in this example. An overheating assessment may therefore assume opening windows without acoustic constraint, and no special facade sound insulation features are required.

Not required – on basis of Level 1 assessment

 

Table B-9 Worked example of Step 3 assessment – considering the effect of potential overheating mitigation strategies on the acoustic conditions – Receptor B

External free-field noise level (dB)

Level 1 risk assessment (in line with Table 3-2)

Notes on overheating mitigation and requirement for Level 2 risk assessment

Level 2 risk assessment (in line with Table 3-3, with mitigation)

Daytime LAeq,16h 58

Night-time LAeq,8h 51

Medium

Level 2 assessment – north east elevations

The anticipated internal levels with a partially open window would be 46 dBA during the day and 39 dBA at night. These levels are consistent with ‘Medium’ risk category in Table 3-3 but are considered to be suitable for occupants given the relatively low number of occasions that windows are required to be open.

Medium, but for limited duration

Level 2 assessment – south west elevations, living rooms

Scenario 1 – Mitigation of noise

Standard opening windows are not considered to be a suitable solution for SW elevations because of the greater number of days on which they are required to be open.

These elevations therefore incorporate measures to mitigating the noise impact. Living rooms have balconies that enable staggered openings into the balcony area, containing sound absorption, so that opening windows are protected from direct noise impact.

Detailed calculations (available on request) demonstrate that the balcony and opening window arrangement achieve a level difference of 16 dB for the incident noise spectrum, while providing sufficient open area to enable control of overheating (the acoustician should cross-reference assumptions used in the overheating assessment).

Thus, while mitigating overheating, the internal noise level is calculated to be 42 dBA during the daytime. This level is consistent with the low end of the ‘Medium’ risk category in Table 3-3 and considered suitable for the number of occasions for which open windows are required.

Low end of Medium

Level 2 assessment – south west elevations, living rooms

Scenario 2 – Mitigation of overheating

Standard opening windows are not considered to be a suitable solution for SW elevations because of the greater number of days on which they are required to be open.

Design team informed of environmental noise constraint in relation to opening windows. Design changes made to the building envelope to reduce heat entering the building. Window sizes reduced, window glazing amended, solar shading added and insulation amended. Enhanced provision of thermal mass.

Risk of overheating substantially reduced without and hence windows are required to be open less frequently and for a shorter duration.

The anticipated internal levels with a partially open window would be 46 dBA during the daytime. This level is consistent with ‘Medium’ risk category in Table 3-3 but considered to be suitable for occupants given the relatively low number of occasions that windows are required to be open.

Medium, but for limited duration

 

External free-field noise level (dB)

Level 1 risk assessment (in line with Table 3-2)

Notes on overheating mitigation and requirement for Level 2 risk assessment

Level 2 risk assessment (in line with Table 3-3, with mitigation)

Level 2 assessment – south west elevations, bedrooms

Standard opening windows are not considered to be a suitable solution for SW elevations because of the greater number of days on which they are required to be open.

These elevations therefore incorporate measures to mitigating the noise impact. Bedrooms have plenum windows that are calculated to provide a level difference between outside and in of 19 dB for road traffic noise, based on the measured incident noise spectra. The overheating assessment confirms that the plenum window dimensions are adequate to suitably mitigate overheating (the acoustician should cross-reference assumptions used in the overheating assessment).

Thus, while mitigating overheating, internal noise levels of LAeq,8h 32 dB are calculated (detailed calculations in accordance with the detailed method in BS 8233 available on request). These levels are consistent with ‘Low’ risk category in Table 3-3 and considered suitable for the number of occasions for which open windows are required.

 

Table B-10 Worked example of Step 3 assessment – considering the effect of potential overheating mitigation strategies on the acoustic conditions – Receptor C

External free-field noise level (dB)

Level 1 risk assessment (in line with Table 3-2)

Notes on overheating mitigation and requirement for Level 2 risk assessment

Level 2 risk assessment (in line with Table 3-3, with mitigation)

Daytime LAeq,16h 64

Night-time LAeq,8h 59

High

Scenario 1 – Mitigation of noise

Standard opening windows are not considered to be a suitable solution.

These dwellings therefore incorporate measures that mitigate the noise impact while providing the air change requirements to mitigate overheating. Both living rooms and bedrooms have acoustically attenuated passive vents (1.25 m high by 0.75 m wide) that are calculated to provide a level difference between outside and in of 25 dB for road traffic noise, based on the measured incident noise spectra. The overheating assessment confirms that the vent dimensions are adequate to suitably mitigate overheating (the acoustician should cross-reference assumptions used in the overheating assessment).

Thus, while mitigating overheating, internal noise levels of LAeq,16h 39 dB during the daytime and LAeq,8h 34 dB overnight are calculated. Calculations in accordance with the detailed method in BS 8233 available on request. These levels are consistent with ‘Low’ risk category in Table 3-3 and considered suitable for the number of occasions for which vents are required to be open.

Scenario 2 – Mitigation of overheating

An alternative method may be to incorporate measures that reduce the need for ventilative cooling (e.g. better external solar shading, incorporating more thermal mass etc), and use a mechanical extract ventilative cooling strategy with smaller acoustically-attenuated façade vents for make-up air.

Low

 

Table B-11 Worked example of Step 3 assessment – considering the effect of potential overheating mitigation strategies on the acoustic conditions – Receptor D

External free-field noise level (dB)

Level 1 risk assessment (in line with Table 3-2)

Notes on overheating mitigation and requirement for Level 2 risk assessment

Level 2 risk assessment (in line with Table 3-3, with mitigation)

Daytime LAeq,16h 72

Night-time LAeq,8h 67

High

Scenario 1 – Mitigation of noise

For these noise levels, opening windows are not considered appropriate even for the limited durations of use that are calculated.

Mechanical cooling is proposed to manage thermal comfort in conjunction with the MVHR ventilation system. An assessment of mechanical noise is required, in accordance with Table 3-6.

Scenario 2 – Mitigation of overheating

With sufficient control of heat gains, an alternative method may be to use a mechanical extract ventilative cooling strategy with small acoustically-attenuated façade vents for make-up air.

Negligible (for external noise)

 

B.7 Supporting information

B.7.1 Passive ventilation solutions providing enhanced sound insulation

Refer to Table B-12 for examples of passive ventilation solutions that are able to provide an enhanced level of sound insulation when compared to a standard opening window providing the same amount of ventilation

Table B-12 Examples of passive ventilation solutions providing enhanced sound insulation

Description and references

Approximate Level Difference

(external free field level – internal reverberant level)

Improvement relative to a window providing the same amount of ventilation

Standard opening windows

Window(s) open sufficiently to provide a ventilation free-area equivalent to 2% of the floor area. [42]

12dB

0dB

Open windows with sound attenuating balconies

Window(s) as above.

Balconies may have a solid balustrade or be enclosed to a further degree (maintaining an open area for ventilation). Absorption may be provided to the balcony soffit or potentially to other surfaces. [48], [49], [50]

16-22dB

4dB – 10dB

Attenuated or plenum windows

Dual windows (spaced by around 200mm) with staggered openings and absorptive linings to the cavity reveals. Various other configurations also possible in principle. [51], [52]

16 – 23dB

4 – 11dB

Attenuated vents/louvres

Ventilation openings with integral means of attenuating sound. Typically this may be acoustic louvres or acoustically lined ducts/plena. [53], [54]

16 – 28dB

4 – 16dB

Attenuated windows or vents/louvres with sound attenuating balconies

Combined use of balconies to provide screening and acoustically attenuated windows or vents. Refer to above for description of each element.

20 – 38dB

8 – 26dB

References

Ref

Title

Author/Publisher

Year

1

ProPG Planning & Noise – New Residential Development

ANC/IOA/CIEH

2017

2

Approved Document F – Ventilation (2010 edition incorporating 2010 and 2013 amendments)

Crown

2015

3

TM59 Design methodology for the assessment of overheating risk in homes

Chartered Institute of Building Services Engineers

2017

4

Zero Carbon Hub – Next Steps in Defining Overheating

Zero Carbon Hub

2016

5

Energy Planning — Greater London Authority guidance on preparing energy assessments

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