Energy Assessment

Air Tightness Testing

Air pressure testing, also known as air tightness or air leakage testing, is a process used to determine the uncontrolled airflow and unwanted drafts in a property that could result in heat loss. A property that fails the test could be considered inefficient in terms of energy usage and costly to heat.

Since 2006, all new builds and conversions must comply with Part L of the Building Regulations, which requires air pressure testing to ensure the property meets energy efficiency standards and has minimal air permeability.

By detecting air pressure and leakage, the airtightness test helps eliminate heat loss and reduce the risk of CO2 emissions, aligning with the principles of modern building regulations.

The air pressure testing process may vary depending on the type of property and the number of homes in a development. Only a portion of homes within a development are tested, and if all homes pass the test, further testing is not necessary.

However, all properties built in accordance with the updated Part L of the Building Regulations introduced in November 2022 will nee an air tightness test and the minimum acceptable air permeability has also been reduced.

Test depressurises the building using a fan and measures the air flow at a range of pressure differentials. The test result expresses the airflow rate across the insulation envelope or internal surface area, in m³/(hr.m²)@50Pa. Air temperature and barometric pressure are taken into account. Smoke tests can identify the source of any leakage and we always offer advice if a building fails a test for being too air tight or too permeable.

The target airflow rate for a new building is described in the Standard Assessment Procedure (SAP) calculations, for domestic dwellings and the Simplified Building Energy Model (SBEM) for commercial buildings.

A building is ready for an air tightness test when:

• 240v mains electric socket is available.

• The integrity of the building structure is complete.

• All external doors, windows and window trickle vents are installed.

• All service penetrations, loft hatches and boiler flue are sealed.

• Extract fans are fitted.

• All chimney flues can be sealed.

• Plumbing is complete and water is in traps.

• Electrical fittings, switches and sockets are installed.

• An external door is available for test equipment.

• All mechanical ventilation can be switched off and temporarily sealed.


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