What’s Happening with TM59?
CIBSE is in the process of updating its TM59 overheating guidance to reflect the latest research, policy priorities, and practical feedback from industry use. The new version is expected to address:
- Alignment with the Future Homes Standard and recent building regulations.
- Improved modelling guidance for naturally ventilated and mechanically cooled dwellings.
- Updates to internal gains, weather files, and adaptive comfort thresholds.
- Enhanced guidance for communal areas and night-time overheating assessments.
However, the revised methodology is still under development and has not yet been released. Until it is officially published by CIBSE, the current 2017 version of TM59 remains the reference standard.
What Are We Doing at IES?
We are closely following the development of the TM59 update and working with relevant stakeholders to ensure our software will be fully compatible with the new methodology as soon as it is released.
We are also:
- Engaging with the CIBSE technical team to understand the forthcoming changes.
- Preparing our Content Store for the proposed CIBSE 2025 DSY weather sets once they become available.
- Developing prototype workflows based on draft proposals to ensure readiness.
- Preparing guidance, templates, and training materials to help you transition smoothly.
What Should You Do Now?
- Continue using the 2017 TM59 methodology until the new version is published.
- Review any overheating risk assessments in the pipeline, particularly for projects likely to be assessed under new planning guidance or future standards.
- Stay connected with us for updates - we will provide clear guidance and software support once the new methodology is released.
Stay Informed
We will keep our users informed as soon as more concrete details become available. Expect further updates via our website, software release notes, and newsletters.
If you have questions or are working on a project that may be impacted, please don’t hesitate to get in touch with our support team.
