An overheating assessment is an analysis of a building to determine the risk of occupant discomfort due to excess temperatures in the building.
Part O is an Approved Document that forms part of the 2021 Building Regulations and it deals with overheating in new residential dwellings. Residential dwellings include single units and blocks of flats, as well as other building types where people sleep on the premises, such as care homes or residential schools.
The intention of the guidance is to protect the health and welfare of occupants, by limiting unwanted solar gains in summer and removing excess heat.
Part O does interact with other parts of the Building Regulations, such as Part L (link), which deals with energy and CO2 emissions, as well as Part Q which covers security and Part F, ventilation.
There are two methods of compliance in Part O. See here.
The first option is the simplified method and this assesses various factors.
The documentation sets limits which need to be met, and this helps demonstrate compliance.
If a building fails the simplified method, the approach is to use the more advanced, DSM method.
The benefit of the dynamic thermal modelling method is it does not impose restrictions on the amount of glazing allowed, so dwellings with increased amounts of glass are best assessed in this way.
There are various methods of combatting overheating. Consideration should be given to the amount of glazing, but even if this is quite high, overheating can be managed using the following design approaches:
Dynamic thermal modelling, also known as DSM / dynamic simulation modelling, is where a 3D model of the building is created and then calculations run to determine internal temperatures throughout the year.
An appropriate weather file is used, based on the geographical location of the dwelling. The underlying methodology for the assessment follows the CIBSE TM59 guidance.
There two main criteria for compliance with Part O, and an additional one for communal corridors, in blocks of apartments.
DSM modelling is often carrie dout in conjunction with the following services:
An overheating assessment is an analysis of a building to determine the risk of occupant discomfort due to excess temperatures in the building.
Dynamic thermal modelling is a computer analysis of a 3D building model, used to assess the risk of overheating.
No, Part O does not apply to extensions but there may be cases where a dynamic thermal model is useful to determine the likelihood of overheating, in highly glazed extensions.
No, Part O is not required for existing dwellings but it would be needed if a large, existing dwelling is converted into multiple dwellings.
No, Part O is for residential dwellings, however a commercial building such as a care home, or residential institution does require a Part O assessment, as people sleep on the premises. Other types of commercial building, such as an office, would be assessed using CIBSE TM52(link to our TM52 page)
Building overheating can be managed in various ways, including reducing solar gain through shading or glazing performance and allowing adequate ventilation, via openable windows and/or mechanical ventilation.
Part O sets two main criteria for overheating, which look at the number of hours the occupied rooms exceed a comfort threshold during the day and the number of hours 26⁰C is exceeded during the night, in bedrooms.
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