Overheating in Domestic Dwellings – Overcoming the challenge

In our series of articles on Part O and the up-and-coming changes, Gurprit Bassi, Wintech’s Associate Director, Façade Engineer & Sustainability Lead, examines the issue of overheating in domestic dwellings.

On the hottest day of the year so far it is apt to consider the issue of overheating. Overheating in residential dwellings has historically not been an issue that has been given serious consideration. With the advent of more energy efficient and airtight homes, as well as the effects of climate change, its effects have become problematic, and increasingly so. The Zero Carbon Hub states that potentially up to 20% of the housing stock in England is already affected and the issue is likely to become more prevalent in the future. Overheating of homes over prolonged periods can have severe consequences for the health of occupants and in extreme cases can be a risk to life.

Whilst certain UK planning authorities have specific overheating requirements, a new Approved Document O has been released by the DLUHC to attempt to address this issue for all new residential dwellings. Its aim is to protect the health and welfare of occupants by reducing the occurrence of high indoor temperatures. To achieve this the guidance seeks to limit unwanted solar gains in summer and provide adequate means of removing excess heat from the indoor environment. It should be noted that this guidance document does not guarantee the comfort of building occupants.

There are two methods to compliance: the simplified method and the dynamic thermal modelling method.

The simplified method bases the risk of overheating on location and limits unwanted solar gains by using external solar shading and glass selection with low G values (<0.4) and high daylight values (>0.7). Cross ventilation is also encouraged, with mechanical cooling only used where ventilation alone is insufficient in removing heat from the indoor environment.

Dynamic thermal modelling follows the methodology in CIBSE TM59 and may offer flexibility over the simplified methodology for some buildings.

In meeting the overheating requirements, sufficient consideration must be given to other performance aspects to prevent their derogation such as: excessive noise at night, minimising air pollution, security, protection from falling and protection from entrapment.

To be able to operate the dwelling as designed and prevent overheating, a home user guide should be created which contains a section on ‘staying cool in hot weather’ to provide the occupant with basic information on how best to maintain a comfortable internal temperature.

Mitigating overheating, whilst also meeting other performance targets may require some serious compromises to be made to the future architectural design of buildings.  Buildings with external shading devices, low G values, proportionally less glazing and larger openable vents are likely to become more commonplace. 

Wintech can analyse overheating on building designs utilising either the simplified or dynamic thermal modelling assessments, and to consider its effect on the façade design, its configuration and associated performance requirements.

Gurprit Bassi MSFE, BSc, MSc

Associate Director