Air Tightness Testing

Air permeability testing — also known as an airtightness test or blower door test — measures uncontrolled air leakage through the building fabric, expressed in cubic metres per hour per square metre of envelope area at 50 Pascals. Required under Part L of the Building Regulations for all new dwellings and non-domestic buildings in England and Wales, the test must be carried out by a certified tester and submitted as part of the as-built SAP or SBEM compliance report before a completion certificate can be issued. Build Energy’s certified testers carry out air permeability tests on residential and commercial buildings across the UK.

Uncontrolled air leakage through the fabric of a building creates heat loss, and significantly affects the energy performance in standard assessment tools like SAP and SBEM.

Air testing is a requirement for new buildings under Part L of the Building Regulations. Our technicians deliver testing across the UK for all types of domestic and non-domestic buildings, and this forms a key part of our end-to-end set of compliance services.

• We can assist with early stage consultancy and design advice
• We provide a seamless service to manage your building regulations compliance when combined with SAP Calculations and SBEM Calculations
• Full UK coverage – no mileage charges
• Vastly experienced team of EAS Accredited engineers
• Advice and consultancy available throughout the design and construction process
• Practical guidance and advice prior to testing
• Smoke investigation to diagnose issues
• Same day certificates when you need them fast

Smoke Diagnostic Testing

Airtightness testing is a mandatory requirement for newly built dwellings under Part L of the Building Regulations – and a pre-requisite for producing final SAP Calculations.

Although some caveats apply for sample testing, most clients will now choose to have every individual dwelling tested in order to meet ever increasing energy efficiency targets.

Airtightness Testing is a mandatory requirement for newly built non-dwellings. Testing is required under Part L2A of the Building Regulations – and is a pre-requisite for producing final SBEM Calculations and BRUKL Reporting.

At Build Energy we can provide not only testing, but early stage consultancy for any type of building, from offices, retail units, schools, and libraries to public buildings and warehouses – regardless of size or location.

For more guidance on air permeability targets and what results mean, see our blog post: Air Permeability Testing – Get Your Building Airtight.

Air tightness results feed directly into SAP calculations for dwellings. For design-stage support, see Air Tightness Consultancy. Other air leakage services include Smoke Shaft Testing and Plenum Testing. Return to the Air Tightness hub.

How does airtightness testing work?

Air tightness testing uses a calibrated fan (blower door) temporarily fitted into a doorway. The fan depressurises the building to 50 Pascals below ambient pressure. The flow rate needed to maintain that pressure difference is measured and divided by the building envelope area to give the air permeability result in m³/h.m² at 50 Pa.

How long does an air tightness test take?

Most tests take between two and four hours on site, depending on the size of the building and any remediation works needed. A basic test on a single dwelling typically takes around one hour. Build Energy can often attend the same day or within 24 hours for urgent completions.

Does every new dwelling need an individual air tightness test?

Not always. Part L1A allows a sampling protocol for large residential developments: types may be sample tested rather than testing every unit. However, all individual dwellings that fail under the protocol must be remediated and retested. Build Energy advises on the most cost-effective approach for each scheme.

What is the maximum permitted air permeability under Building Regulations?

The current maximum permissible air permeability under Part L1A (England) is 10 m³/h.m² at 50 Pa. Most energy consultants set a design target of 5 m³/h.m² or better to give headroom. Buildings targeting Passivhaus certification must achieve 0.6 ACH at 50 Pa.

Can Build Energy test both residential and commercial buildings?

Yes. Build Energy carries out air permeability tests on new dwellings under Part L1A and on non-domestic buildings under Part L2A. For specialist enclosures, we also provide Smoke Shaft Testing and Plenum Testing.

For practical guidance on preparing your site before test day, see what you can seal for an air tightness test.

What is a good air tightness test result?

A good result for a new dwelling is 5 m³/(h·m²) or below – well within the 8 m³/(h·m²) maximum permitted under Part L1A of the Building Regulations. High-performance builds typically target 3 m³/(h·m²) or better, and Passivhaus certification requires 0.6 air changes per hour at 50 Pa pressure. For non-domestic buildings, Part L2A applies the same 8 m³/(h·m²) limit. The lower the result, the less heat is lost through uncontrolled air leakage and the better the building’s SAP or SBEM energy performance rating.

How many air tightness tests are required?

For residential developments, a test is required on three dwellings of each type or 50% of dwellings – whichever is the lesser. Untested dwellings must use the average result for tested dwellings of the same type plus a +2 m³/(h·m²) penalty margin. To ensure all dwellings reliably meet the 5 m³/(h·m²) target, the design air permeability (DAP) should be set no greater than 3 m³/(h·m²). For non-domestic buildings, all new commercial and public buildings are generally required to test under Part L2A as part of the SBEM process.