Air Tightness Testing

At the time of writing the methodology for EPC assessments of existing dwellings is RDSAP 9.94. The much anticipated RDSAP 10 update has not happened yet and a significant methodology overhaul from RDSAP to the Hone Energy Model (HEM) is proposed for 2025.

Air tightness testing is usually carried out using a 'Blower Door' which is temporarily fitted in an external door frame of a property.

A large fan in the blower door draws air into the property and the air pressue inside and outside of the property are consinuously monitored.

A measurement is taken of how much airflow is required to maintain a pressure difference of 50Pa between the inside and outside of the property.

Considering the scale of possible results, a smaller value indicates the property is more airtight, and will therefore lose less heat due to draughts and air moving through the property, and therefore less energy is required to replace that lost heat.

Air tightness testing is compulsory for building regulations as part of the construction process for new-build properties but it is possible to commission a test on an existing property if you wished.

Whether it's worth getting such a test carried out on your existing property however might need some thought. Firstly, we'll consider when it will be possible to use such a test result.

The methodology used to produce Energy performance Certifictes (EPCs) for existing dwellings is known as RDSAP (Reduced Dataset Standard Assessment Procedure).

The current version of RDSAP is 9.94 and this version of the methodology does not provide a mechanism for entering the result of an air tightness test.

The long awaited RDSAP, 10 update however (now due in Q1 2025, at the earliest) will support the entry of an air tightness test result.

If you have an air tightness test carried out on your home, and the result of that test is better (lower) than the assumed (default) air tightness value that would otherwise be applied by the RDSAP methodology for your property, then your EPC rating might improve.

More information to follow about this shortly.....

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