Overheating

Recent years have seen an increased risk of overheating in many new homes, which is often an unintended consequence of better insulation and improved airtightness. This has led to a number of studies most notably from the DCLG, NHBC Foundation and the Zero Carbon Hub, all of which highlight enhanced fabric performance as a significant cause. While more insulation is advantageous during the heating season, it can also trap unwanted heat during the summer months. Poor ventilation is also contributing to the problem, leading to a growing separation between the temperature experienced inside and outside the home.

Single-aspect flats and apartments are identified as being at particular risk of overheating, especially in city locations where delivering effective ventilation can be challenging. Alongside reduced fabric heat loss, there is a range of other aggravating factors that can come together to cause overheating, which are set out in an NHBC Foundation Guide. This and other guidance on tackling overheating identifies the provision of adequate ventilation as the most effective design measure that can be applied. Alongside adequate ventilation, other techniques including shading, the use of thermal mass and night cooling are highlighted as effective techniques to control overheating.

Summary of design strategies

  • Prevent - As far as possible, stop heat from entering through effective shading, ideally located externally. Internal gains from appliances and services should also be minimised where practicable.
  • Reject - Get heat out of the building using ventilation when the air outside is cooler than inside. Night-time ventilation is particularly effective and design measures should be applied to ensure this can be achieved in a secure manner.
  • Absorb - Use the thermal mass provided in concrete and masonry dwellings to soak up heat inside the building and then purge it using night-time ventilation. Dwellings can reap the benefits of thermal mass easily by using sympathetic internal finishes that allow heat to be absorbed by the fabric.
  • Design - Take advantage of the significant opportunities relating to orientation, fabric and form (including openings) available at the design stage to enhance overheating resilience. These options cannot be exploited later.
  • Education - Ensure the occupants understand the basic design intent with regard to the control of overheating. This centres on: the use of shading; when and how to ventilate; the role of the building fabric in helping to maintain a comfortable environment.
For more information, download The Concrete Centre guide on Overheating.