Technical Guidance - Keeping Cool: Avoiding overheating risks
Category: Guidance
Avoiding Summer Overheating
Published: May 2021
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Recent summer heatwaves have made us more aware than ever that the risk of overheating in both new and existing buildings demands attention - and is likely to become even more of a concern as our climate warms.
As a comfort driven approach, the Passivhaus standard includes a summer overheating criterion which requires that internal temperatures do not exceed 25ºC for more than 10% of the year. However, as with all models, the assessment is highly dependent on the assumptions that are made during the modelling process. We need to ensure that the result remains robust when those assumptions vary, for example as occupant behaviour changes, or as the climate warms.
To meet this need, the Passivhaus Trust has developed detailed guidance accompanied by a PHPP plugin covering design strategies to reduce risk, limitations and constraints that may have an impact, key indicators of the likelihood of risk, and a series of stress tests to demonstrate robustness.

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PHT Summer Plugin for PHPP
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The PHT Summer plugin for PHPP provides summary guidance on design strategies, an interactive analysis of risks, limitations and constraints, a dynamic generator of key indicators of overheating risk pulled from your PHPP data, and also (PHPP 9 version only) a series of stress tests that apply to all users.
The plugin is available free to download for both PHPP 9 and for PHPP 10. In PHPP 10.x, the stress testing element of the plugin has been incorporated into core PHPP, so that has been removed from the PHPP 10 version of the plugin.
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Summer Comfort Statement for Passivhaus Certification
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To ensure summer comfort, Passivhaus certification requires written documentation of the strategy for thermal comfort in summer, signed by the building owner. This should be issued to the building certifier as part of the certification documentation, alongside the relevant section of the handbook for the building user.
The sample Summer Comfort Statement provided here has been put together by the Passivhaus Trust and the UK Certifiers Circle to be used as a template for this purpose. The statement identifies the critical assumptions that underpin the design, and the summer comfort strategy, as well as overheating risk results and stress testing.
This template can also be used for buildings with active cooling, presenting the expected results for active cooling instead of overheating risks.
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Further information
Keeping Cool: avoiding overheating risks - On demand short-course
Previous PHT story: Sweltering summers? No Sweat! - 07 August 2018