TM59 Overheating Assessment: What Is It and Do I Need It?

This blog post explores CIBSE TM59 Overheating Assessments, a dynamic thermal modelling method that prevents overheating in your new home. Building regulations require assessments of overheating risk in new builds and major renovations.

In this blog you’ll learn:

• What a CIBSE TM59 Overheating Assessment is and how it works
• The advantages compared to simpler methods
• Whether you need TM59 for your new build project
• The benefits of a TM59 Overheating Assessment

What is a TM59 Overheating Assessment?

Imagine a computer simulation of your new home, taking into account everything from the size and orientation of windows to the materials used in construction. This is essentially what CIBSE TM59 does. It uses sophisticated dynamic thermal modelling software to analyse how your home will respond to different weather conditions throughout the year, pinpointing any potential risks of overheating.

Compared to simpler methods, TM59 offers a more accurate picture. It considers not just the overall energy efficiency of the building, but also factors like:

• Solar gain: How much sunlight your home absorbs through windows.
• Building orientation: How the sun’s path affects different sides of the house.
• Internal heat sources: Appliances, occupants, and other factors that generate heat inside.
• Building location: A dynamic assessment uses weather files for the specific site and takes into account local shading factors like surrounding buildings and landscaping. This provides a more nuanced understanding of how these elements will impact the building’s thermal performance throughout the year.

Do I Need CIBSE TM59 Overheating Analysis?

All new dwellings require an overheating assessment according to Approved Document O of the Building Regulations. While CIBSE TM59 is one way to achieve this, it is not always mandatory. and Here’s how to decide if it is right for your project:

• Building complexity: Large windows, open floor plans, or significant internal heat sources can increase overheating risk. TM59 provides a more precise assessment for these complex designs.
• Local planning requirements: Some local authorities may require TM59 for specific projects, even if a simpler method technically applies with regulations. Check with your local building control team to see if it applies to yours.
• Simplified Method Limitations: The simpler overheating assessment method may not account for factors like:
  • Glass Properties: The g-value (solar heat gain coefficient) of windows significantly impacts heat gain. TM59 can factor this in.
  • Shading Nuances: The effectiveness of overhangs, reveals, and shading from nearby buildings can be more accurately modelled with TM59.

Benefits of a TM59 Overheating Assessment:

Using CIBSE TM59 for your new build project offers several advantages:

• Enhanced comfort: Avoid an uncomfortably hot home, especially during summer. By identifying potential overheating risks early on, adjustments can be made to the design to ensure a comfortable living environment.
• Energy efficiency: TM59 can help optimise your building design to minimise overheating and reduce reliance on air conditioning, leading to lower energy bills.
• Compliance assurance: Ensure your new home meets overheating regulations and avoids potential delays or additional costs associated with non-compliance.
• Future-proof investment: A comfortable and energy-efficient home is more valuable in a changing climate, with increasingly hot summers becoming the norm.

In summary, if your project has any of the complexities mentioned above, or you prioritise a high level of comfort and design certainty, then a TM59 Overheating Assessment could be a suitable method.

Conclusion

A TM59 Overheating Assessment is a valuable tool for ensuring your new home is comfortable, energy-efficient, and compliant with building regulations. While not always mandatory, it offers significant benefits for specific projects. Discussing your project with a sustainability consultant can help you determine if CIBSE TM59 is the right choice for you.

We offer a comprehensive range of overheating calculations, including TM59 Overheating Assessments. Contact us today to discuss your project specifications and work with us to ensure that your new home is cool, comfortable, and future-proof.