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Overheating Assessments
Clear guidance on overheating compliance requirements for new buildings. When assessments are required and how to demonstrate compliance.
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TL;DR - Overheating Assessments
Design → Assessment → ComplianceWhat is an overheating assessment?
An overheating assessment is the way you demonstrate that your new build complies with overheating regulations.
Does a new house need an overheating assessment (Part O)?
All new dwellings need to comply with Part O. Most pass Part O using the simplified method.
Do commercial buildings need an overheating assessment?
It's not part of the building regulations, but sometimes planning authorities can request one.
What do you need from me?
Plans + site orientation + spec (windows/heating/build-ups).
Will Building Control accept your reports?
Yes, we produce compliant reports for both domestic and commercial buildings.
How long does it take to get compliance reports?
This depends on the size of your project. Typically we turnaround overheating assessments in 2–4 days.
Ready to get moving?.
*Typical once plans/spec are received. Complex plots may take longer.
What is an Overheating Assessment?
An overheating assessment is used to calculate the risk of summer overheating in buildings. For new residential buildings in England & Wales, it is a Building Regulations requirement under Approved Document O and in Scotland, Building Standard 3.28.
Approved Document O (Part O) of the Building Regulations applies to residential developments, including new build houses and flats. Introduced in 2022 (2023 in Scotland), Part O & Building Standard 3.28 aim to reduce the risk of overheating in new homes by requiring designers to consider solar gains, glazing, ventilation and layout at an early stage.
An overheating calculation is completed at design stage and, for new dwellings, assessments follow the CIBSE TM59 methodology. A simpler prescriptive method is also available for lower risk projects
Overheating assessments may also be carried out for non-domestic or communal spaces, such as shared areas within apartment buildings or purely commercial buildings. In these cases, the CIBSE TM52 methodology is used where overheating risk needs to be assessed.
An overheating assessment will look at factors like:
- Glazing levels and orientation
- Ventilation strategies
- Solar gains and shading
- Occupancy patterns and use of spaces
It is important to distinguish between comfort modelling and regulatory compliance assessments. While both consider internal temperatures, an overheating assessment for compliance is focused on meeting defined criteria set out in guidance (Part O and CIBSE), rather than subjective comfort alone.
Part O Overheating Assessments
All new dwellings in England, Wales and Scotland require an Overheating Assessment.
There are two routes to compliance.
- Simplified Method
- Dynamic Simulation Model (DSM) - TM59
Most homes pass Part O with the simplified method, but some homes, particularly those with high amounts of glazing or lack cross ventilation need to go down the Dynamic Simulation route with the CIBSE TM59 methodology.
Part O & TM59 Assessments
Non Domestic Overheating Assessments
There is no building control requirement for a non domestic new build to have an overheating assessment. However, there are situations where a design may need one:
- Planning Authority mandate
- BREEAM Certification
- Best practice for occupant comfort
CIBSE TM52 is the methodology used for overheating assessments in commercial spaces. There is no simplified method for commercial overheating assessments, this is always a Dynamic Simulation Model of the building.
TM52 AssessmentsOur Overheating Assessment Process
Send us your plans & specification
Email or upload your drawings (plans, elevations, sections), site location/postcode, and basic spec details (windows, ventilation strategy, build-ups, heating system).
We review & recommend the best route
We’ll check whether your project can pass using the simplified method or if TM59/TM52 dynamic modelling is required.
Modelling & assessment
Using approved software we run the calculations against CIBSE weather data and the relevant compliance criteria.
Clear report delivered
You receive a Building Control ready report with results, any mitigation recommendations, and confirmation of compliance.
Revisions if needed
Changes to the design? No problem. Reasonable revisions are included within the original quote.
Typical turnaround is 2–4 working days once we have everything we need.
Start Your Assessment →What We Need From You
- Site location
- Floor plans, elevations, sections & a site plan
- Window & door schedule (sizes, g-values, frame types)
- Construction build-ups
- Proposed heating system
- Proposed ventilation strategy (e.g., trickle vents, MVHR, opening windows)
- External shading details (overhangs, brise soleil, balconies etc.)
Need help? No problem. Send what you have and we’ll let you know if anything else is required.
Upload Plans & Get a Quote →Overheating Assessment Frequently Asked Questions
Do all new homes need an overheating assessment?
Yes. All new dwellings in England, Wales and Scotland now require an overheating assessment to comply with Part O (or Building Standard 3.28 in Scotland). Most projects pass using the simplified method, but designs with high glazing, single aspect layouts or limited ventilation often need the full TM59 dynamic modelling route.
How much does an overheating assessment cost?
Prices start from as little as £195 for straightforward projects that qualify for the simplified method. TM59 dynamic simulation assessments are priced individually once we review your plans. We always provide a fixed quote upfront with no hidden extras.
How long does an overheating assessment take?
Once we have your plans and specification, most overheating assessments are completed and delivered within 2–4 working days. We can often prioritise urgent projects, just let us know your deadline.
Do commercial buildings need an overheating assessment?
There is no mandatory requirement under Building Regulations for purely commercial buildings. However, many projects require a TM52 assessment for planning conditions, BREEAM credits or to demonstrate occupant comfort. We regularly provide TM52 reports for offices, retail and mixed use schemes across the UK.
What happens if my design fails the overheating assessment?
A fail on the first run is very common and nothing to worry about. We provide clear, practical mitigation recommendations (e.g. improved shading, ventilation changes or glazing adjustments) and include reasonable revisions in the original price until your design passes.
Will Building Control accept your overheating reports?
Yes. All our Part O and TM52 reports are produced by qualified assessors using approved software and follow the exact CIBSE methodologies required. They are accepted by Building Control bodies nationwide.
Can you bundle an overheating assessment with SAP calculations?
Absolutely. Many clients save time and money by bundling Part O overheating with their SAP calculations. We use shared data across both services for faster turnaround and consistent results. Ask for a combined quote when you get in touch.
What information do you need for an overheating assessment?
We need your plans (floor plans, elevations, sections), site postcode/orientation, window/door schedule, ventilation strategy and construction details.