Part O Overheating Assessments
Building Regulations Compliance & Dynamic Thermal Modelling
What is Building Regs Part O?
Approved Document Part O forms part of the UK Building Regulations and specifically addresses mitigating overheating risks in new residential dwellings. This legislation applies to single houses, blocks of flats, and other residential structures where people sleep on the premises, such as care homes or student accommodations.
The primary objective of the guidance is to protect occupant health and welfare by limiting unwanted solar heat gains during summer months and ensuring design strategies can effectively remove excess heat.
How it interacts:Part O works closely with other sections of the Building Regulations, notably Part L (energy efficiency and CO₂ emissions), Part F (ventilation strategies), and Part Q (security considerations for ground-floor openings).
There are two primary pathways to demonstrate compliance with Part O: the Simplified Method and Dynamic Thermal Modelling.
The Two Methods of Compliance
Part O Simplified Method
The Simplified Method is a prescriptive checklist approach designed for straightforward residential layouts. It limits the maximum area of glazing relative to the floor area of the building and dictates minimum free areas for window openings to ensure adequate natural ventilation. It is highly recommended to engage our team as early in the architectural design stage as possible to prevent restrictive glazing limitations.
Part O Dynamic Thermal Modelling
Dynamic Simulation Modelling (or DSM) utilises advanced software to construct a precise 3D digital profile of your building design. The software simulates real-world internal temperatures hour-by-hour across an entire calendar year.
Geographic Weather Files: The calculations incorporate localised historical weather data files based on the specific geographical location of the proposed development.
CIBSE TM59 Methodology: The underlying calculations follow the strict CIBSE TM59 assessment framework required by local authorities and building control.
Multi-Zone Criteria: Compliance requires meeting strict thermal comfort thresholds for both daytime living spaces and nighttime bedrooms, alongside specific limits for communal corridors in apartment blocks.
Our Dynamic Thermal Modelling services are frequently executed in tandem with our other core compliance services:
SAP Assessments / OCDEA – Part L1 calculations for new dwellings
SBEM Calculations – Part L2 energy assessments for non-domestic/commercial buildings
BREEAM Credits – Evidence mapping for HEA01, HEA02, and HEA04 validation
What We Do
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EPC
Required when a building is constructed, sold or let. Covering Devon, Cornwall, Somerset and beyond.
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SAP Calculations
New build and conversion energy calculations for residential properties.
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SBEM Calculations
Commercial new build and conversion energy calculations.
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Part O — Overheating
Dynamic thermal modelling for residential overheating compliance.
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Thermal Modelling
Advanced building energy modelling including BREEAM, TM52, TM59 and ventilation.
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ESOS
Lead Energy Assessor qualified audits for ESOS compliance.
Frequently Asked Questions
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An overheating assessment is an analysis of a building to determine the risk of occupant discomfort due to excess temperatures in the building.
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Dynamic thermal modelling is a computer analysis of a 3D building model, used to assess the risk of overheating.
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No, Part O does not apply to extensions but there may be cases where a dynamic thermal model is useful to determine the likelihood of overheating, in highly glazed extensions.
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No, Part O is not required for existing dwellings but it would be needed if a large, existing dwelling is converted into multiple dwellings.
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No, Part O is for residential dwellings, however a commercial building such as a care home, or residential institution does require a Part O assessment, as people sleep on the premises. Other types of commercial building, such as an office, would be assessed using CIBSE TM52(link to our TM52 page)
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Building overheating can be managed in various ways, including reducing solar gain through shading or glazing performance and allowing adequate ventilation, via openable windows and/or mechanical ventilation.
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Part O sets two main criteria for overheating, which look at the number of hours the occupied rooms exceed a comfort threshold during the day and the number of hours 26⁰C is exceeded during the night, in bedrooms.
Read our Google customer reviews
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"Efficient, friendly, professional. Asked for an EPC for our residential property, had the certificate the following day. Assessor was very thorough and personable during his visit and with correspondence."
Emma Fancett – Domestic EPC
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"We had to obtain 39 EPC certificates for a student building and Up Energy carried out the whole certification process for us, efficiently and quickly and always keeping us well informed."
Jeffrey Seed – Student accommodation, Exeter
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"I have worked with Up Energy on several projects now and they have always delivered on time while being easy to work with. Their pro-active approach makes the production of energy calculations and final certification at the end of a project a simple process."
Tim Thompson – Repeat client, energy calculations and certification
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07515 442665 (Simon)
07974 567272 (Alistair)
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