Homes in the UK are increasingly at risk of overheating, affecting the comfort and health of residents, especially if it impairs sleep.
Overheating in dwellings is only expected to worsen with climate change – a fact that has led to the introduction of the Building Regulations Part O, a new requirement to assess and limit the risk of overheating in homes and other types of residencies.
Keep reading to learn more about the requirements of Part O Building Regulations, including the impact on energy efficiency and the consequences of non-compliance.
What Are Building Regulations Part O?
In 2021, Building Regulations Part O were introduced to address the growing problem of overheating in residential buildings. These regulations aim to limit unwanted solar gain during summer periods and provide occupants with adequate means of removing excess heat from indoors.
Overheating in buildings can result from several factors, including large sun-exposed windows, limited shading over the property, and insufficient summer ventilation. In some areas, occupants may even be unable to open windows for long periods due to external noise or safety concerns.
Part O Building Regulations apply to all residential and institutional dwellings, including care facilities, student accommodation, and anywhere else someone could stay overnight (excluding hotels). As with all Building Regulations, compliance with Part O is a legal requirement.
Key Requirements of Part O: An Overview
Developers and designers of new residential buildings in the UK must factor in the requirements of Building Regulations Part O at an early stage of the design and development process. Guidance for complying with Part O is found in “Approved Document O: Overheating” (ADO).
ADO considers factors such as the proportion of glazing (windows) relative to the size of the property, the orientation of the glazing to the sun at different times of the day, and the location of building (distinguishing between buildings in a “high risk location” and a “moderate risk location”).
If the proportion of glazing is too high, for example, then other methods of minimising solar gain must be considered – such as passive cooling means.
How Part O Affects Building Design & Layout
Reducing the risk of overheating must form part of the design process, while also considering other key elements, such as views, daylight, ventilation, and optimal winter solar gains.
Building Regulations Part O may have an impact on the design of new dwellings by requiring builders and developers to:
- Change the size & quantity of windows
- Change the extent of openable windows
- Adjust the layout for optimal cross ventilation
- Use solar control glass or external shading devices (e.g., shutters or overhangs)
- Use mechanical ventilation systems
- Carry out thermal modelling to identify potential overheating risks
Compliance with Part O: Steps for Builders & Developers
Because Building Regulations Part O is a relatively new requirement, the risk of overheating in building design has not been considered to this degree. Consequently, it should not be assumed that existing designs will automatically comply.
When designing and constructing new residential properties, developers and builders must make reasonable provision to limit unwanted solar gains in summer and provide an adequate means to remove heat from the indoor environment.
The assessment (and thus demonstration of compliance with Part O Building Regulations) can be achieved in the following two ways:
- The Simplified Method: Compares ratios of window-to-floor area, sets maximum values, and considers location / direction. The design is compliant if values are not exceeded.
- Dynamic Thermal Modelling (DTM): Employs DTM software to demonstrate that the building does not exceed a certain internal temperature for a certain amount of time.
Dynamic thermal modelling allows more variables to be considered, such as mechanical cooling and G-values of glazing. It must be carried out if the windows cannot be opened.
The Impact of Part O on Energy Efficiency & Sustainability
For many years, Part L of the Building Regulations (“Conservation of Fuel & Power”) has been concerned with preventing heat leakage from buildings to reduce the UK’s carbon footprint.
To achieve optimal energy efficiency, Part L rewards increased insulation, high thermal performance, and low air leakage rates – all of which are still a requirement.
This is challenging because the introduction of Part O Building Regulations requires the opposite – providing occupants with greater means of removing excess heat from indoors.
More concerning is that, if there are no natural means to expel heat from the dwelling, the reliance on air conditioning units to cool buildings will consume a significant amount of energy, potentially leading to non-compliance with Part L.
Penalties for Non-Compliance with Part O Building Regulations
As with any requirement under the Building Regulations, non-compliance with Building Regulations Part O may result in the proposed development not being “signed off” by Building Control. Non-approval would mean that the property cannot be sold, rented, or occupied.
Overheating Analysis Services from Stroma
Stroma’s experienced team of energy assessors provide overheating analysis services to help ensure compliance with Building Regulations Part O. We work with designers and developers to inform the design process at any early stage, offering simplified and CIBSE TM59 assessments for both domestic and non-domestic buildings.
For more information about Part O and Part L compliance, please contact the Stroma Built Environment team.
FAQs: Part O Building Regulations
Does Part O apply to existing buildings?
Currently, Building Regulations Part O do not apply to existing buildings. However, there is consultation to include “Material Change of Use”, whereby an existing non-residential building that has been converted to a residential property would require Part O compliance.
What is Approved Document O?
An Approved Document (AD) is guidance to help comply with a specific Building Regulation. “Approved Document O: Overheating” offers compliance guidance for Building Regulations Part O.
What does “limiting solar gains” mean?
Solar gains are the increase in temperature due to the sun’s radiation. This can cause the internal space of a building to heat up and become uncomfortable, which is why solar gains must be limited.