Dynamic Overheating Assessment for Part O, TM59 and TM52 Compliance

Innervision Design has qualified dynamic thermal simulation modellers and consultants and can offer clients a range of dynamic overheating modelling and assessment services, including Part O, TM59 and TM52 compliance assessments.

We strive to provide a high-quality service with competitive rates and a quick turnaround, while offering our clients cost-effective and practical solutions.

1. Why use dynamic thermal modelling for overheating risk analysis

As the global climate continues to warm, and modern buildings increasingly incorporate larger areas of glazing and high-performance building fabric, overheating is becoming an increasingly important issue for homes and buildings in the UK.

The newly introduced Building Regulations Approved Document O (Part O), which came into effect on 15 June 2022 in England, sets out the legal and technical requirements for mitigating the risk of overheating in new residential buildings.

Part O of the Building Regulations provides two methods for demonstrating compliance:

• The simplified method, which prescribes maximum areas of glazing and minimum free areas of openings within rooms and buildings to limit solar gains and facilitate the removal of excess heat.
• The dynamic thermal modelling method, in accordance with CIBSE TM59, which provides greater design flexibility and enables a more detailed assessment of overheating risk.

Some planning authorities, such as the Greater London Authority, required dynamic overheating assessments several years before the introduction of Part O.

Dynamic thermal modelling uses advanced computer simulation to predict a building's thermal performance over time. It takes into account a wide range of design parameters, including construction details, hourly weather data, detailed occupancy schedules and internal heat gains, and typically analyses these at short time intervals, such as hourly or sub-hourly intervals. Consequently, dynamic thermal modelling can provide a more detailed and accurate representation of a building's thermal performance than simplified assessment methods.

We use industry-leading DesignBuilder dynamic simulation software to construct three-dimensional models and assess overheating risk.

2. Part O and TM59 dynamic overheating assessment for dwellings and residential institutions, to comply with the Building Regulations and local planning policies

Part O requires new dwellings, and new residential institutions (e.g., student accommodation, care homes and prisons etc) to comply with CIBSE TM59 dynamic thermal standards. Part O of the Building Regulations will not apply to non-residential buildings.

CIBSE TM59:2017 (Design methodology for the assessment of overheating risk in homes) defines an industry standardised approach to predicting overheating risk for residential buildings using dynamic thermal analysis.

3. CIBSE TM52 dynamic overheating assessment for non-residential buildings, to comply with local planning policies

CIBSE guide TM52, 2013 (The Limits of Thermal Comfort: Avoiding Overheating in European Buildings’), defines an industry standardised approach to predicting overheating risk for non-residential buildings using dynamic thermal analysis.

CIBSE TM52 is required by some local planning authorities (for example, the Greater London Authority).

4. Innervision Design Part O, TM59 and TM52 dynamic overheating assessment services include:

• Construction of detailed 3D model of your buildings
• Comprehensive data input (e.g. u-values, thermal mass, external shading, HVAC, openings and free areas)
• Dynamic simulation modelling using various DSY1, DSY2, DSY3 weather files if required
• Guidance on overheating mitigation strategy based on cooling hierarchy to ensure compliance. Passive measures will be prioritised (e.g. shading, low-g windows)
• A detailed and easy to read report for your submission to Building Control Body or related planning authorities.

5. Part O compliance using the simplified method 

The Part O Simplified Method prescribes maximum areas of glazing and minimum free areas of openings within rooms and buildings to limit solar gains and facilitate the removal of excess heat. Therefore, Part O can have a significant impact on the conceptual design, as glazing areas and free areas of openings are important design elements that need to be carefully considered.

Architects should incorporate an overheating mitigation strategy at the planning stage. Otherwise, approved schemes may be subject to costly and time-consuming design changes later, at the Building Regulations technical design stage, to achieve compliance with Part O.

For Part O compliance, we recommend getting in touch with us as early as possible, preferably at the planning stage, for a preliminary Part O compliance assessment using the Simplified Method. We will thoroughly review your conceptual plans and check that the glazing areas and free areas of openings comply with the requirements. If a project does not pass the Simplified Method, we will advise on cost-effective solutions to achieve compliance.

Not every project will be suitable for the Part O Simplified Method. Where dynamic overheating modelling is required, we will advise you accordingly. This assessment would normally be undertaken at the Building Regulations compliance stage.