How Air Tightness Testing and Smoke Surveys can Fix Leaky Buildings

On previous projects we have used combined air tightness testing and smoke surveys to identify the air leakage paths in houses and commercial buildings.

How Air Tightness Testing and Smoke Surveys can Fix Leaky Buildings

On previous projects, we have used combined air tightness testing and smoke surveys to evaluate and fix air leakage paths in houses and commercial buildings. On many projects we have encountered very ‘leaky’ dwellings and commercial buildings, that had air leakage rates in excess of 40m3/h/m2. Using combined air tightness and smoke testing surveys we managed to identify the air leakage paths for our client’s air sealing teams to target thus lowering the air leakage rate down to a respectable 5m3/h./m2. 


Its common knowledge that excess air leakage can accounts for between a third and half of a typical home's heat loss. Yet it’s often quite difficult to pinpoint air leakage and heat loss through the building envelope in both new building and conversion projects. Air tightness testing and smoke surveys provide a powerful combination, as it provides an accurate and visual approach to identifying and controlling air leakage in in buildings. Our blower door equipment can be set up quickly with minimal disruption to projects, and the test and smoke survey can be carried out in a matter of minutes, meaning that you can quickly establish buildings air leakage rate, as well as producing an accurate air leakage survey report, highlighting the air leakage paths within the building envelope, to allow targeted remedial sealing works minimising time and costs.




when it comes to the designed air leakage target, different types of buildings require different levels of air tightness. Air-conditioned buildings should be tighter than naturally ventilated ones with air leakage targets less than 3m3/h./m2. Laboratories, isolation suites and archives facilities can be between 0.2 to 2.0m3/h./m2, so are designed to be much more air-tight to ensure humidity, heat loss and the ingress of pollutants help to a minimum and within specification - these types of buildings need careful design and installation management of the air leakage line, due to their low target figure/s. 


How do you undertake a blower door smoke survey?

Our blower door fan mounts into a door-sized housing, that can be adjusted to suit the size of the door frame.

We then set up the blower door equipment as follows.


  • Firstly, we temporarily install a blower door fan system (depending on building size) in a suitably placed doorway.
  • We then take a series of environmental measurements such as internal and external temperatures as well as barometric pressures.
  • We then turn on the fan equipment and take measurements between 25-70Pa in 5Pa increments, recording the pressure differential at each step.
  • Finally, our technicians will calculate the total air flow required to achieve a pressure differential of 50 Pa, divided by the total building envelope area - this calculation will show leakage rate in m³/h.m² @ 50 Pa.
  • Once the building air leakage rate has been established, we then pressurise the building (blows air into) to around 50 pascals of pressure. This forces air to flow through cracks or air leakage paths throughout the building envelope.
  • We then turn on the smoke machine and walk around the building recording all the air leakage paths through the building envelope.

it usually takes one to two hours to complete each air tightness smoke test; however, we can attend site all day if instructed. This allows time for the operatives to comprehensively seal all the necessary air leakage paths on the day of the test. If you are planning on undertaking remedial sealing works on the day of the test, your operatives will need to have mastic, expanding foam, draught excluders, plasterboard, grip fill and suitable safe access to undertake the sealing works. Here is a video of a typical smoke survey to a dwelling.




If some of the areas are difficult to reach such as very tall commercial buildings, we can also undertake a Thermography survey. This is performed using an infra-red camera to identify hot and cold spots on the surface of the building; this requires a temperature variation and is often done at night.


What is Equivalent Leakage Area (ELA) in buildings

Our equipment and software compare the air blown through the fan to the pressure drop across the blower door equipment. This gives then produces the relative tightness result for the house. Our computer software then converts the pressure drop to an equivalent leakage area (ELA), which is the overall size of a single hole in the building fabric that would equate to the same amount of air leakage.

The equivalent leakage area (ELA) is very useful for our engineers and clients to understand the cumulative effect of the many small leaks - such as leakage along a skirting board - that are present within a typical building as they may add up to the equivalent of an open door or window on the building.


What types of Smoke machine do you use?  

When it comes to smoke test surveys, we use 3 different types of smoke machines.  We have a smaller handheld smoke machine for standard houses. We then have our middle size smoke machine which uses pressurised smoke canisters, which is extremely useful for large houses and smaller commercial buildings and smoke shafts etc. we then have our large smoke machines that fill a large commercial building in minutes.

So, to recap, we use the different size smoke machines on the following buildings:

  • Small smoke machine – houses, flats, and laboratories
  • Mid-size smoke machine – small commercial buildings and smoke shafts
  • Large smoke machine – large commercial buildings

In all instances, we always use our smoke machines with our blower door systems to accurately identify the air leakage paths in buildings. Without the inclusion of a blower door system to pressurise the entire building, you will only see small amounts of ‘wispy’ smoke drift, which makes it very difficult to identify and record the exact air leakage areas.  


Common Air Leakage Paths Identified During Smoke Surveys

  1. Poorly installed windows and doors which do not close tightly
  2. Windows and doors with missing seals
  3. The gap at the wall/skirting board junction.
  4. Perimeter and internal wall/floor junctions.
  5. Gaps around service penetrations (such as water and electrical) through floor and walls
  6. Pathways through ceiling voids into masonry cavity walls
  7. Pathways through eaves in cavities
  8. Gaps around windowsills and door reveals
  9. Gaps around bathroom and WC services
  10. Gaps around kitchen and utility services.
  11. Gaps between dry lining and ceilings
  12. Unsealed chimneys
  13. Gaps around electrical and IT fittings
  14. Gaps around ceiling loft hatches
  15. Ventilation penetrations through the walls, ceiling, and roof
  16. Poorly installed extractor fans to kitchens, utility, and bathrooms


We Can Identify Your Air Leakage Paths

At APT Sound Testing we have large amount of experience in understanding the requirements of Approved Document L, along with extensive experience of carrying out thousands of successful air tightness tests on a wide range of developments across London and the UK.

In order to achieve the required air tightness target (which is getting lower all the time) and to avoid the risk of a failed air tightness test, we strongly recommend that early consideration is given to the design of the air leakage line within your project.


By working with our customers throughout their design and construction stages, we can provide advice and guidance on the most feasible ways to avoid air leakage and attain compliance for the air tightness test. Please download our air tightness checklist to help you prepare for your test.


At APT Sound Testing, we are happy to provide you with general air leakage design advice for your building envelope and onsite guidance. Upon completion of your project, we provide Nationwide UKAS Accredited Tightness Testing for domestic and commercial buildings to help you demonstrate Building Regulation Part L Compliance.


To find out more about our air tightness testing service or if you wish to discuss your project please contact us on 01525 303905 or email us at info@aptoundtesting.co.uk