Part O Overheating

Part O Overheating Assessments for New Residential Buildings

Crowther Solutions provides Part O overheating assessments for new residential buildings in England, using either the Simplified Method or Dynamic Thermal Modelling where appropriate. Approved Document O is intended to limit unwanted solar gains and provide adequate means of removing excess heat, helping demonstrate compliance with the overheating requirements of the Building Regulations.


When is a Part O Overheating Assessment Required?

Part O applies to new residential buildings in England where an overheating assessment is required to demonstrate that the design limits unwanted solar gains and provides adequate means of removing excess heat.

The assessment should be considered during the design stage, particularly where dwellings include large areas of glazing, restricted window openings, limited cross-ventilation or high levels of solar exposure.

Early assessment can help identify potential overheating risks before the design is finalised and may reduce the need for more significant changes later in the project.


Our Part O Assessment Methods

1. The Simplified Method

The Simplified Method provides a straightforward Pass or Fail assessment against the limits set out in Approved Document O. It is primarily driven by glazing areas and the amount of openable area available for removing excess heat, together with factors such as location, orientation and cross-ventilation.

Because the method uses prescribed limits, there is relatively little flexibility if the proposal fails. In many cases the practical options are to reduce glazing areas, increase the available openable area, or revise the proposed design so that it falls within the simplified criteria.

2. Dynamic Thermal Modelling

Dynamic Thermal Modelling provides a much more detailed assessment of how the dwelling is likely to perform during periods of hot weather. Rather than relying solely on prescribed glazing and opening limits, the model can take account of the actual building geometry, construction, window g-values, external shading and overhangs, ventilation strategy and other overheating mitigation measures.

This can be particularly useful where large areas of glazing are an important part of the design. If the Simplified Method would require smaller windows or larger openings, Dynamic Thermal Modelling may allow alternative measures such as solar-control glazing, external shading or, where appropriate, mechanical cooling to be assessed instead.

Where a project does not initially meet the required criteria, we can model alternative options provided by the project team and show how they affect the overheating assessment.

Part O assessments are undertaken to demonstrate compliance with the overheating requirements of the Building Regulations using the criteria set out in Approved Document O. The assessment helps identify and reduce the risk of overheating, but it cannot guarantee that a completed building will never overheat in use, as actual performance can be affected by weather conditions, occupant behaviour, ventilation use and the final construction.


What Information Is Needed for a Part O Assessment?

The information required will depend on the assessment method being used, but typically includes:

  • Plans, elevations and sections

  • Window and door sizes

  • Window opening details

  • Glazing g-values where available

  • Building orientation

  • External shading, balconies or overhangs

  • Ventilation strategy

  • Details of any proposed overheating mitigation measures

Providing this information at an early stage helps ensure the assessment reflects the proposed design accurately and allows potential compliance issues to be identified sooner.


Practical Part O Compliance Support

Crowther Solutions can support both the SAP assessment and Part O overheating assessment for the same project, helping ensure the information used across both assessments remains consistent. Factors such as window sizes, glazing g-values, U-values, shading and ventilation can influence the results of both assessments, so changes made to improve one area may need to be considered against the other.

By dealing with both assessments, we can highlight where proposed changes may affect SAP performance or Part O compliance and provide clear technical guidance to the project team. The final design and specification remain the responsibility of the appointed designer.


Part O Overheating Assessment FAQs

Do all new dwellings need a Part O assessment?

Part O applies to new residential buildings in England where the requirements of Approved Document O are relevant. The appropriate assessment method will depend on the building design and project circumstances.

What happens if the Simplified Method fails?

If the Simplified Method fails, the design may need to be amended to reduce glazing areas, increase openable areas or improve ventilation. In some cases, Dynamic Thermal Modelling may provide a more detailed assessment and allow alternative mitigation measures to be considered.

Can solar-control glazing help with Part O compliance?

Yes. Solar-control glazing with a suitable g-value can reduce solar gains and may help improve overheating performance, particularly when assessed using Dynamic Thermal Modelling.

Can Crowther Solutions complete SAP and Part O together?

Yes. We can undertake both the SAP assessment and Part O overheating assessment for the same project, helping ensure the design information used across both assessments remains consistent.


Request a Part O Assessment Quote

Send us your project information and we’ll review the assessment requirements and provide a project-specific quotation.

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Part O Overheating