Air Tightness

Air Tightness Testing

Building Compliance Testing Limited can provide you with a fast and cost effective ATTMA Accredited Air Tightness Testing across Mainland UK, in accordance with BS EN ISO 9972:2015 and CIBSE TM23.


green tick BCTAir Tightness Testing

Also known as air leakage testing, air infiltration testing, air pressure testing or air permeability testing, is a test required by the Part L of the Building Regulations as part of an overall energy performance assessment of a building. Air leakage is calculated as cubic metres of air leakage per hour per square metre at 50 Pascals (or 4Pa for Pulse Testing). But what does this actually mean?

What is Air Leakage?

Air leakage can occur through gaps and cracks in the fabric of the building envelope, allowing conditioned (heated or cooled) air to escape, which consequently driving up heating/ cooling bills and contributing to potentially to carbon dioxide emissions, in the form of mains gas or non-renewable electricity sources.

How long does an Air Test take?

Typically the test takes between twenty minutes to a couple of hours. This all depends of the size of the building, the test locations, the ability to create stable pressure in the building and unfortunately the controllable influence of the British weather.

Typically a test is carried out by a single engineer using a UKAS calibrated blower door system. The system is essentially a fan mounted within a canvas, that’s installed within an external door or window, controlled by a fan speed controller, and a number of tubes connected to a multi-channel manometer, which is read and inputted into a software to generate a result.

During this time other trades can remain within the building so long as the external envelope remains closed (external doors and windows) and internal doors open.

Pre-test Preparation

The building must be in a state of readiness, with all external doors and windows fitted and operational. Internal doors should be open, and any ventilation systems should be turned off.

Airtightness testing is a government-regulated procedure to measure the amount of air that seeps through gaps and cracks in buildings. It’s a crucial part of building regulations in London, and if you own a residential property or commercial business you need to ensure that you meet these targets.

Air leakage can cause significant heat loss, higher C02 emissions and expensive heating bills. This can be a real pain for homeowners, landlords and businesses so it’s important that buildings are properly sealed in the first place.

We’ll start by carrying out a thorough inspection of your property, ensuring that it’s ready for testing. This includes a full building check, which will include walls, doors, windows and skirting.


Air Test Results and Reporting

The technician will record the results of the test, which will include the air permeability rate (measured in air changes per hour, or ACH), and any areas of the building that failed to meet the required standard. This will be reported on a short-form report – ATTMA Certificate. A full report and Part L photographic evidence can be provided on request. The technician will prepare a written report that includes the test results, any areas of concern, and recommendations for remedial actions. This report must be submitted to the building owner and to the relevant building control authority.

The Air Pressure Testing Standards

In Approved Document Part L1 of the Building Regulations, the process of assessing a building’s air tightness is commonly referred to as Pressure Testing. This methodology, as defined in ATTMA Technical Standard 1, is based on internationally recognized standards like BS EN Standard 13829:2001 and ISO 9972:2015. For new dwellings, as stipulated in Approved Document L1, airtightness tests are mandatory for any new build dwelling or development comprising two or more dwellings/flats, with the number of tests contingent on the development’s size and layout. Compliance with Part L1A necessitates that any tested dwelling achieves an air pressure test result (or air permeability) of 10m³/h/m² or less at a pressure differential of 50 pascals. Similarly, under Approved Document L2, which pertains to new non-dwelling buildings, air permeability tests are also required for new build premises other than dwellings, with the quantity of tests contingent on the development’s size and configuration.

Air Tightness Testing Equipment

As expected, the equipment used for Air Permeability Testing is highly specialized and demands frequent and rigorous calibration to ensure precision. All equipment from Building Compliance Testing is calibrated by a UKAS approved laboratory to guarantee accuracy during on-site tests. Building Compliance Testing is registered with ATTMA, subject to regular audits to uphold high standards and accuracy. If you’re uncertain about whether your development necessitates an Air Permeability Test, Building Compliance Testing can provide guidance. We also offer complimentary, no-obligation quotes at highly competitive rates for projects of all sizes.

Is Your Project Ready For Air Testing?

Check out our Air Permeability Testing site status checklist to see if you are ready – just click here. Free to download.

Your Building Compliance Partner – Air Tightness Consultancy

Whether your requirements is for a domestic retrofit, residential or commercial development, to eco-build passivhaus testing, Building Compliance Testing can support you from concept to completion by offering a one-stop-service service:

design reviews – site inspections – pretesting – smoke diagnostics – site management training and education

Learn more about our Air Tightness Consultancy by clicking here.

Testing and ATTMA Certificate for as little as £45+VAT

Book now >


We don’t just offer Air Testing. Bespoke testing and other complimentary services include:

– Part L Compliance

– Smoke Shaft Testing for Automatic Opening Ventilation (AOV)

Room Integrity Testing

Smoke Testing

Multi-fan Commercial Testing

– Existing Buildings Testing

– Air Tightness Design Reviews

– Plenum and Raised Access Testing (RAF) to BG65 Standards

Passivhaus Testing

– Air Sealing in preparation for Air Tightness Testing


Air leakage testing, a requirement under Part L of the Building Regulations, assesses a building’s energy performance by measuring the volume of air escaping per hour per square meter at a specific pressure level (usually 50 Pascals). This test helps identify gaps and cracks in the building envelope, through which conditioned air can escape, leading to increased heating or cooling costs and potential carbon dioxide emissions. Conducted using a calibrated blower door system, the test takes approximately twenty minutes to a few hours and involves a fan, manometer, and software to determine results. Building Compliance Testing offers a comprehensive service, including design reviews, site inspections, and training, alongside other services such as smoke testing, air tightness design reviews, and Passivhaus testing, to ensure compliance and energy efficiency in various building types.


green tick BCTAir Testing Frequently Asked Questions

Questions? We’ve Got Answers!

Find below a list of common frequently asked questions about Air Permeability Testing.

What is required for an Air Tightness Test?
  • Floor Plans and Section Drawings
  • Site Address and Contact
  • A copy of the Design-stage SAP report for dwellings
  • A copy of the Design-stage BRUKL report for buildings other than dwellings i.e retail units
What is an Air Test also known as?
  • Air Testing
  • Air Infiltration Testing
  • Air Pressure Testing
  • Air Leakage Testing
  • Heat Loss Testing
What is Part L of the Building Regulations?
  • This is an approved document named

    Conservation of fuel and power: Approved Document L

  • It is an amended building standard stating that all new dwellings must be built in compliance with current energy conservation objectives and as such sets the requirements for Air Tightness Testing.
What am I allowed to temporarily seal for an Air Tightness Test?

Background trickle ventilators, passive ventilation systems and any permanently designed uncontrolled natural ventilation (such as a chimney flue). Mechanical ventilation and air conditioning systems should be turned off and isolated.

When do I know when I am ready for an Air Tightness Test?
  • We will carry out the air tightness test once the unit is past the second fix stage and the following
    elements within the unit are completed:
  • All walls are finished, including cladding, windows and doors.
  • Skirting boards are fitted and sealed around
  • Sockets and lights are fitted and completed, in some cases caulked around (mention potty pads)
  • All plumbing work is completed and gaps or holes around the service pipes are sealed.
  • Leakage around the door frame, threshold and window boards are sealed.
How long does an Air Tightness Test take?

In most cases, air tightness testing can be completed in as little as one hour and usually does not take longer than two hours. For larger projects with more complex testing requirements, access, time and preparation could take between two to four hours. This is to allow for the appropriate temporarily sealing.

What is a good air tightness test score?

Airtightness testing in the UK, governed by Part L of the Building Regulations and Scottish Building Standards, serves a crucial role in enhancing energy efficiency and occupant comfort in new buildings. Mandated minimum leakage standards set by the government aim to curtail energy consumption, thereby lowering heating bills and fostering better living conditions. Moreover, a superior airtightness rating can potentially elevate a property’s market value.

Recent scrutiny of airtightness test outcomes in the UK unearthed a significant correlation between results and energy targets, highlighting a policy-driven incentive for adherence to best practices. However, this emphasis on meeting targets sometimes leads to measures that fall short of optimal efficiency. This phenomenon affects airtightness uniformly across various ventilation systems.

The significance of a good airtightness test score lies in its reflection of a building’s ability to retain heat while keeping moisture at bay. The Air Changes per Hour (ACH) value, endorsed by building regulators, serves as the yardstick for assessing a building’s airtightness. A commendable airtightness rating effectively curbs heat loss through minute cracks and mitigates the risk of condensation and mould formation.

Airtightness stands as a cornerstone of energy-efficient construction practices, not only curbing heating expenses but also contributing to environmental conservation by minimizing heat wastage. However, the realm of airtightness testing is not flawless, necessitating ongoing research and refinement.

A desirable score typically falls within the range of 3-5 m3/h-m2 at 50 Pa, indicative of robust energy performance.

What is Passivhaus?

Passivhaus is a voluntary design standard for energy efficiency in a dwelling, aiming to produce low-energy, efficient and sustainable buildings. Under Passivhaus buildings in development must meet strict guidelines in areas such as air tightness, heating and ventilation. Learn more about Passivhaus Air Testing by clicking here.

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Building Compliance Testing TransparentBuilding Compliance Testing empowers the built environment sector to deliver projects that go beyond environmental planning and building regulation compliance.

From concept to completion, we provide all your compliance needs under one roof.

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