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Part O Overheating Assessment
Expert guidance on Part O overheating requirements for new build homes. Assessments launching soon.
Join the waiting list to be notified when full Part O assessments become available.
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What Is Part O?
Part O of the Building Regulations sets the requirements for limiting overheating in new residential buildings. It applies to most new build houses and flats, and in some cases to newly created dwellings formed from a change of use. The aim is to make sure homes stay comfortable in warm weather and avoid excessive solar gain.
Under Part O, overheating risk must be assessed using either the simplified method (based on glazing limits, cross-ventilation and shading) or a more detailed dynamic calculation. Your assessor will confirm which approach is needed for your development.
Although our full Part O assessment service is not yet live, we provide clear guidance on when an overheating assessment is required and what information you will need to prepare.
When Does Part O Apply?
Part O applies to new dwellings in England and is mandatory for Building Control sign-off. A Part O overheating assessment is usually required when:
- You are building a new house, flat or maisonette.
- Your design includes large areas of south-facing glazing.
- The building is located in a higher risk area, such as London or dense urban zones.
- Cross-ventilation is limited due to layout or orientation.
- A simplified method check suggests overheating risk.
If you are unsure whether your project requires a Part O assessment, send us your drawings and we will confirm this free of charge before the service launches.
What Will Be Included in Our Part O Service
Our full Part O assessment service is currently in development. When launched, it will provide a complete overheating review for Building Control, tailored to new build homes and developments.
- Full Part O compliance check using the simplified method where applicable.
- Dynamic overheating assessment for dwellings that fall outside simplified limits.
- Assessment of glazing, orientation, shading, ventilation and solar gain.
- Clear recommendations to reduce overheating risk where needed.
- Reports suitable for submission to Building Control.
- Email support throughout design and compliance stages.
Join the waiting list to receive updates and early access when this service becomes available.
What We Will Need for a Part O Assessment
You can prepare for your future Part O assessment by gathering the following drawings and specifications:
- Floor plans with dimensions.
- Elevations and sections.
- Site plan showing orientation and surrounding buildings.
- Glazing sizes and specifications, including g-values if known.
- Ventilation strategy (natural, mechanical, MVHR).
- Shading details such as overhangs, fins or nearby obstructions.
Even if you do not have all of this information yet, you can still join the waiting list and receive guidance on what will be required when assessments open.
Part O Frequently Asked Questions
Do all new homes need a Part O assessment?
Yes. All new dwellings in England must demonstrate compliance with Part O. Some homes will meet the simplified criteria automatically, while others will need a detailed assessment.
Is Part O the same as a SAP calculation?
No. SAP calculations assess energy performance under Part L, while Part O looks specifically at overheating risk. Many projects now require both assessments for Building Control.
Can glazing cause a Part O fail?
Large areas of south-facing glazing often trigger overheating risk. Overheating can usually be addressed through improved ventilation, shading or specification changes.
When will your Part O service be available?
We expect Part O assessments to become available soon. Join the waiting list to receive updates and early access.
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