Air Tightness Testing

Testing for Air Tightness

Air tightness testing is a recognised method of measuring the extent to which air is lost through leaks in the building fabric. It is sometimes referred to as air leakage testing or air pressure testing. When testing for air tightness the pressure differential is measured across the envelope of the building be means of a large fan installed temporarily sealed and a range of static pressures and environmental readings are taken. The fan is switched on and the air pressure in the property is gradually increased or decreased and the differential pressure is recorded at each step. The total air flow required to achieve a pressure differential of 50 Pa is calculated and divided by the total building envelope area to provide the leakage rate in m3/hr/m2.


 On each development air tightness testing should be carried out on three units of each dwelling type or 50% of all the instances of that dwelling type, whichever is less. A block of flats should be treated as a separate development irrespective of the number of blocks on the site.

Depending on the size of the property, the duration of the air tightness test should take no longer than 2 hours with the air tightness test certificate issued some 2 days later.

It is best to make sure that the building is fully prepared for the air tightness test, in most cases the main areas of air leakage are through penetrations in the kitchen and/or utility room and through penetrations in the bathrooms and cloak rooms. Other common air leakage paths are through the wall/floor junction, light fittings and boilers rooms and service cupboards.

Our fan systems are compact, discreet and fit simply into a personnel door. The system can easily be transported through areas of limited access or up to high level areas. It is for this reason that many companies working in busy city centres utilise our expertise and equipment. We are able to eliminate the site disruption caused by the larger trailer type testing equipment. Work can also continue inside the building whilst the air leakage test is being carried out.

In the event of a building failing an air tightness test,  we can offer smoke testing, which highlights the areas of leakage in the building fabric. We can then undertake a full written and photographic survey as reference for your site management and relevant subcontractors. We will also offer free advice on the best method to seal any leaking areas. The main benefits of this are:

  • Air leakage is quickly identified in the event of a test failure
  • Remedial works can start straight away
  • Practical completion can be achieved more quickly

If you require air tightness testing or domestic ventilation testing, we have the knowledge and experience to ensure your building passes first time. If you require more information please contact me direct on 07775 623464 or e-mail me at:

Air Tightness Testing in London

Air Tightness Testing in London 
Unfortunately air test failures at the pre-completion stage of a project can prove hugely costly in regards to the financial and programme in regards to the handover of the development.

If you ask Air Pressure Testing to be involved at the design stage of the project we can look at the design of the building envelope which usually saves our clients expensive and difficult remedial works at the pre-completion stage of a project.

In summary we can help our clients achieve compliance with Part L of Building Regulations by offering the following consultancy services:

blower door

Air Tightness Design review

We will carry out a review of the building envelope to identify any potential weak areas that may cause excessive air leakage and subsequently perform poorly during the air tightness testing.

Site Survey Inspection of Building Envelopes.

During the construction of the project we can visit the site and inspect the workmanship and envelope junctions. A report will be produced highlighting any areas of concern and/or poor workmanship that may lead to potential air tightness testing failure.

We can check that buildings/s air tightness elements are fit for the intended purpose and will have the expected life span. Our operative’s expertise, skills and experience provide clients with pragmatic design solutions; to minimise the risk of the air tightness failure and fire enclosure test failure.
We have experience of auditing and advising on the correct air sealing works on all types of projects from a small server room enclosures – such as such as hospital intensive care units) right up to large distribution warehouses with floor areas in excess of 1000m2.

Our air tightness Test reports can be prepared, providing a schedule of works, which are cross referenced with relevant locations and corresponding photographs, this allows for a quick and easy site reference for all of your site staff and sub-contractors. Site audits should be carried out at critical points during the build programme, i.e. during the main construction of the external envelope. This will ensure that any potential problems are identified prior to the installation of ceilings etc. which makes remedial works very difficult due to restricted access. It will also reduce the chance of damage caused by operatives trying to access the air leakage areas.

In one such instance, our on-site expertise was used to good effect during the construction of four isolation rooms. The contract specification included an item for the Contractor to achieve an air permeability rate under 1m³/h/m². By carrying out site audits and site visits, the contractor achieved the stringent air tightness specification at the first attempt. This was achieved despite the air tightness test target being ten times lower than the standard building regulations standard.

If the building fails the air tightness test, we can quickly undertake a low impact smoke test for rapid visual diagnosis of air leakage paths. As part of our standard air testing equipment we carry both hand-held and large commercial building smoke generators. When the buildings pressurised the smoke is forced out through air leakage paths thereby providing conclusive evidence of areas requiring attention. During the air testing it is essential that you have a competent person such as your Site/Project manager available to witness the smoke test, so the site team has an understanding of the project/s air leakage paths and can start the sealing works straightaway. It is also essential that the site team have the correct materials on site so that the remedial sealing works can be started straight after the smoke test has been undertaken.

Whether you need air tightness design/consultancy service or just a simple air tightness test, we have the knowledge and experience to ensure your building passes first time.

If you are unsure of the air tightness services you require, please call us on 07775 623464 or e-mail:

How Is an Air Tightness Test Undertaken?

How is an air tightness test undertaken?

A temporary airtight screen is fitted into the entrance door of the dwelling with water traps filled (or temporarily blocked), trickle vents closed (sealed under Part L 2010) and extract vents sealed – we send out a full checklist to help our client prepare for the air tightness testing.

A fan is then mounted in the screen and operated to blow air into or out of the dwelling to create a pressure difference between inside and outside of approximately 50 Pa.


The air tightness of the dwelling is quantified by measuring the rate of airflow through the fan while a range of pressure differences between the inside and outside of the dwelling is maintained.

  1. Approved Document L sets out the applicable regulations for England and Wales.
  2. Approved Document L1A sets out the air tightness requirements for new dwellings.
  3. Approved Document L1B states that reasonable provision should be made for continuity but no test requirements in existing dwellings.
  4. Approved Document L2A deals with new buildings other than dwellings.
  5. Approved Document L2B provides that extensions to buildings (other than dwellings) where the extension/s

A dwelling must achieve an air permeability result of 10m3/hr/m2, however most instances this has now been reduced to 5m3/hr/m2.

The designed air permeability rate is defined in the design stage SAP and often imposes a more stringent target. If the tested air tightness result is greater than that used in the design stage SAP, the as-built SAP may not comply and you may fail the air tightness test.

A test that does not achieve a Building Regulations minimum performance requirement would be classed as a air tightness fail. Should tests fail to achieve the necessary performance level, the property may need a smoke test and thereafter once the air leakage paths are identified remedial sealing works can be undertaken with final re-testing. In some instance the you may be asked to test further examples of that dwelling type to restore confidence and show that remedial actions have been carried forward into the remainder of the build.

If you require air tightness testing on your project, please contact us at, or call me direct on 07775623464.

What is Air Tightness Testing

What is Air Tightness Testing?

Air leakage, air permeability and air tightness are all terms that refer to the uncontrolled loss of air from inside a building to the outside and the infiltration of air coming from outside to inside. This loss or gain of air through cracks, holes or gaps in the fabric of the building is often felt to us as draughts through air leakage paths.

blower door

Trying to achieve a good level of air tightness is important for the energy efficiency of the building. The benefits of improved insulation and more energy efficient heating systems are lost if warm air simply leaks out of the building and cold air can leak in. Poor air tightness can be responsible for up to 40% of heat loss from buildings resulting in much higher heating costs I winter and cooling costs in summer.

It’s important to have an air tightness test completed on the property. This allows a figure – in m3/hr/m2) to be put on the amount of air gained and lost. The attained air leakage rate can then be measured against what’s acceptable and what’s not in the eyes of the building regulations. A good practice figure is currently set at 5m3/hr/m2 which is quite easy to achieve and can drastically reduce the ongoing heating costs of the building.

If you require air tightness testing on your project, please contact us at, or call me direct on 07775623464.