Part L2A regulations:

There is now a testing requirement for buildings above 500m² GIFA.

The test standard has changed for buildings over 500m²GIFA and is now based on the Air Leakage rate that is used in the DER calculation (Design Emission Rate)

Buildings below 500m² GIFA do not require a test if a leakage rate of 15 m³/m²/h is used to calculate the DER.