With UK temperatures rising, ensure your building stays cool and legally compliant. Our accredited Energy Consultants carry out CIBSE TM59, TM52, and Part O simplified assessments nationwide.
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An overheating assessment is a crucial thermal model that helps ensure buildings stay cool, comfortable, and safe as UK summer temperatures continue to rise. With climate change making extended heatwaves more common, managing your building's internal climate without over-relying on carbon-heavy mechanical air conditioning is now a strict legal requirement under Approved Document O.
Modern, highly insulated and airtight buildings are fantastic for saving energy in winter (Part L), but they easily trap heat in the summer. Whether you are constructing a high-rise flat in London, an office space in Manchester, or a residential block in Birmingham, our team uses TM52 (commercial) and TM59 (residential) methodologies to examine how your building handles thermal gain based on materials, layout, and cross-ventilation.
Our dynamic thermal modelling software analyzes several crucial architectural choices to predict how your building will react to intense summer heat.
The direction your building faces makes a massive difference. A home in Manchester with large south-facing or west-facing windows will absorb significantly more solar radiation during peak hours compared to a north-facing elevation.
Good airflow is essential for passive cooling. Whether it’s openable windows or mechanical systems, buildings in dense cities like Birmingham need proper purge ventilation to stop heat from building up in airtight designs.
Too much glass turns a room into a greenhouse. In high-density areas like London where sun exposure is prolonged, glazing ratios (G-values) and external shading devices (brise soleil, shutters) are critical to passing the assessment.
Dense building materials (like exposed concrete or brick) absorb heat during the day and release it at night. In places like Liverpool, utilizing the correct thermal mass strategy helps stabilize indoor temperatures during volatile heat spells.
How often people use a space, the equipment they run, and how many people are present contribute heavily to internal heat gains. A busy office will naturally warm up faster than a residential bedroom, altering the required mitigation strategies.
We know that overheating risks vary wildly depending on location and design. We offer two distinct assessment pathways to ensure your building stays cool, energy-efficient, and fully compliant.
Our Simplified Method follows the prescriptive guidance laid out directly in Approved Document O. It is ideal for straightforward buildings like small residential homes, low-rise flats, or simple offices in lower-risk locations like rural areas or suburban Birmingham.
You receive a Part O Compliance Report confirming your design passes the prescriptive simplified method, ready for Building Control.
For complex designs, buildings with large amounts of glazing, heavily insulated structures, or sites located in 'High Risk' warmer areas like central London or central Manchester, Dynamic Thermal Modelling is legally required to prove compliance.
You receive a comprehensive Dynamic Modelling Report (TM59/TM52) that proves compliance even for complex, high-risk architectural designs.
In recent years, the UK construction industry has faced a unique paradox. As Building Regulations (specifically Part L) demand increasingly higher levels of insulation and extreme air tightness to reduce winter heating bills, we have inadvertently created buildings that trap heat during the summer. This has led to the introduction of Approved Document O (Part O).
If you are developing homes, flats, or care facilities, the assessment will be conducted using the CIBSE TM59 methodology. This standard looks at two main criteria to define overheating:
1. The living spaces (living rooms, kitchens, bedrooms) must not exceed a certain temperature threshold for more than 3% of the occupied hours during the summer period (May to September).
2. Bedrooms have an additional, much stricter rule: The temperature must not exceed 26°C for more than 1% of the sleeping hours (10 PM to 7 AM). This ensures that occupants can achieve healthy, restful sleep during heatwaves.
If your initial design fails the dynamic model, our accredited energy consultants will work with your architects to implement passive design strategies. Common and highly effective mitigations include:
Blocking the sun before it hits the glass is the most effective strategy. We model the addition of deep roof overhangs, external shutters, or louvres to reduce direct solar gain.
We can recommend altering the glass specification. Low-g value glass (solar control glass) allows visible light to enter the room while reflecting the infrared heat radiation back outside.
Increasing the size of openable windows or altering how far they can open allows for greater cross-ventilation, rapidly cooling the thermal mass of the building during the evening.
While internal blinds offer some relief, they are generally considered less effective than external measures, as the heat has already penetrated the building envelope. We model them carefully based on exact fabric properties.
If your project is a non-domestic building (like an office, school, or retail space in Leeds or Sheffield), the assessment falls under CIBSE TM52. This standard relies on the concept of 'Adaptive Thermal Comfort', recognizing that people in offices tolerate different temperatures than people trying to sleep in a home.
If you’re building something new or making major material changes to an existing property, especially in high-density urban areas like Manchester or London, you will likely trigger a Part O assessment requirement from Building Control.
This is particularly critical for developments with single-aspect flats (apartments with windows only on one side, preventing cross-ventilation), buildings located near noisy roads (where occupants cannot open windows to cool down due to acoustics), and properties featuring large architectural glazing.
We handle complex thermal modeling for developers across the entire UK.
Everything you need to know about securing overheating compliance for your new build.
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