introducing part O
Part O of the building regulations, which took effect in England from June 2022, sets out requirements for mitigating overheating in new residential buildings. This is usually achieved through a combination of limiting unwanted solar gain while removing heat through natural ventilation. The part O approved document provides detailed guidance on maximum glazing areas and minimum opening areas – which vary according to a variety of factors.
Where windows cannot be left open at night ‒ for reasons of noise or security ‒ then alternative means of removing heat must be provided, which should be passive wherever possible. Combined with a heat pump, UFH systems run in reverse offer a passive or near-passive means of heat removal. We are currently gathering evidence to support this approach to mitigating overheating, which is explained in more detail in our paper ‘UFH? That’s Cool’. Register to download below.
PART O - KEY CLAUSES
OVERHEATING
O1 Overheating mitigation
(1) Reasonable provision must be made in respect of a dwelling, institution or any other building containing one or more rooms for residential purposes, other than a room in a hotel (“residences”) to –
(a) limit unwanted solar gains in summer;
(b) provide an adequate means to remove heat from the indoor environment.
(2) In meeting the obligations in paragraph (1)—
(a) account must be taken of the safety of any occupant, and their reasonable enjoyment of the residence; and
(b) mechanical cooling may only be used where insufficient heat is capable of being removed from the indoor environment without it.
REMOVING EXCESS HEAT
2.10 Excess heat should be removed from the residential building by any of the following means.
- Opening windows (the effectiveness of this method is improved by cross-ventilation).
- Ventilation louvres in external walls.
- A mechanical ventilation system.
- A mechanical cooling system.
2.11 The building should be constructed to meet requirement O1 using passive means as far as reasonably practicable. It should be demonstrated to the building control body that all practicable passive means of limiting unwanted solar gains and removing excess heat have been used first before adopting mechanical cooling. Any mechanical cooling (air-conditioning) is expected to be used only where requirement O1 cannot be met using openings.
NOISE
3.2 In locations where external noise may be an issue (for example, where the local planning authority considered external noise to be an issue at the planning stage), the overheating mitigation strategy should take account of the likelihood that windows will be closed during sleeping hours (11pm to 7am).
SECURITY
3.6 When determining the free area available for ventilation during sleeping hours, only the proportion of openings that can be opened securely should be considered to provide useful ventilation. This particularly applies in the following locations, where openings may be vulnerable to intrusion by a casual or opportunistic burglar.
- Ground floor bedrooms.
- Easily accessible bedrooms.
3.7 Open windows or doors can be made secure by using any of the following.
- Fixed or lockable louvred shutters.
- Fixed or lockable window grilles or railings.