The CIBSE TM59 report or Technical Memorandum 59 is a methodology for assessing overheating in residential buildings. This includes homes, care homes and student halls of residence that are newly built or substantially refurbished. Using dynamic thermal analysis, architects and developers are able to identify areas where internal temperatures could be too high for sustained periods.
How does TM59 relate to part O building regulations?
Overheating assessments are required for Part O of the building regulations for new build residential projects. This is to prevent homes from being unreasonably warm. It states that, where possible, natural ventilation should be used, either opening windows (both sides of the building preferably) or natural ventilation grilles.
What are the requirements of TM59?
The requirements differ depending on the room type. There are two criterion:
- Hours of exceedance – The number of hours that the temperature in living rooms, kitchens, and bedrooms exceeds the threshold comfort temperature by 1K or more during a typical non-heating season should not be more than 3% of occupied hours
- Night hours above 26 °C – the temperature in bedrooms from 10 pm to 7 am should not exceed 26 °C for more than 1% of annual hours.
Living rooms and kitchens must adhere to the first criterion but bedrooms must meet the requirements of both. If the TM59 report shows the risk of overheating, preventative measures must be taken.
How do you prevent overheating?
This starts with design, reducing the amount of glass, considering the orientation of the building. Architects also design in brise soleil shading, insulation and even planting.
Opening windows are one of the main ways to purge heat from a building. However, this should only be considered if there is no pollution or excess noise. In the event of excessive noise, it is possible to install acoustic vents which allow air to pass through whilst dampening sound.
Read our case study about acoustic ventilation here.
