Overheating and Part O

As homes become more highly insulated, it is less easy for unwanted heat to escape during the summer months, resulting in a greater risk of overheating; a problem that is further compounded by a warming climate.

Alongside adequate ventilation and shading, the thermal mass provided by masonry construction offers another means of tackling overheating. Masonry’s thermal mass allows it to absorb and later release excess heat, helping smooth out the gains and stabilise the internal temperature. Heat stored in masonry is expelled at the end of the day by ventilating the building with cool night air. The combined benefit of thermal mass and night ventilation is accounted for in the SAP overheating check, which allows a reduction in the peak internal temperature of up to 3.5°C compared to an equivalent lightweight dwelling with night ventilation.

Overheating in homes is increasing for two key reasons:

  1. Summertime temperatures are gradually rising as our climate continues to warm.
  2. There is a greater tendency for modern, highly insulated and airtight homes to overheat as heat is more easily trapped.
As explained above, guidance on tackling overheating identifies the provision of adequate ventilation and shading as being the most effective design measures to apply. Other techniques are also identified including the use of thermal mass with night cooling, which offers a further means of helping to control overheating.

Designing to avoid overheating – Download Now. This version of the guide (updated in 2022) covers information on the new Building Regulation Part O, which deals specifically with overheating in new residential properties.

In addition to offering guidance on the use of thermal mass, this publication also provides an overview of the new Part O regulations, which deal specifically with overheating in new residential buildings and sets out new requirements for delivering safe and usable overheating measures.

Visit the overheating web page to learn more.