Air Tightness of Existing Buildings

What we do

We undertake air tightness testing of existing houses, flats, offices and other buildings as part of a wider strategy for improving their energy performance.

Projects range from refurbishment of large offices seeking BREEAM Excellent to individual homeowners wishing to reduce their energy bills and draughts.

Air tightness is a key element of an effective energy strategy for any building. It works alongside insulation in ensuring the building fabric allows you to retain heat/keep the cold out and make the most of any other energy-saving measures that have been put in place.

Insulation alone will not prevent cold air infiltration and loss of heated air through the fabric of the building, it needs to be upgraded alongside reducing air leakage to maximise the benefits.

Our approach is typically along the following lines:

Initial air tightness test on the building/property to establish the current levels of air permeability and identify the air leakage paths (using air flow and/or smoke). Depending upon the scale/location of the leakage, it is often possible to immediately/temporarily remedy some of these to quantify the level of improvement

Provide a written summary confirming performance levels (relative to standards for newbuilds/low energy schemes), list the key areas of current leakage with suggestions for how to address them

If desired by the client, carry out a further air tightness test to confirm the improvement in air permeability performance following remedial works. This figure can be used as part of an energy calculation model  (SAP/SBEM) to confirm the impact on the overall energy efficiency of the building and produce a higher energy rating on the Energy Performance Certificate (EPC).

How it works

Our Air Test Engineers are home-based and well-placed to cover Greater London and the City, Kent, Essex, Surrey, Sussex, Hampshire, Berkshire, Buckinghamshire, Hertfordshire and Bedfordshire, we are able to test all over the UK.

Our process is as follows:

  1. We provide a quote based on the size of the building and location – it is usually helpful to have PDF Plans to calculate the size of larger buildings
  2. We provide a checklist and agree a date
  3. We call you ahead of the test date to talk you through the preparation and process and agree the timings. We would also look to confirm the air permeability that has been targeted in the energy model at this stage, if it hasn’t been discussed already. The results of the test are a key component of the calculation of the overall energy efficiency of the building and, therefore, achieving the necessary air tightness is a critical part of building control sign-off.
  4. On houses and flats we would typically complete the temporary sealing for the test when we arrive on site. For larger buildings, we would talk you through what would need to be done in advance of our arrival.
  5. We conduct the test. Testing is done through a pressure test whereby fans are installed into a doorway of the building and used to create a measurable difference between the pressure inside and outside of the building. The amount of air needed to maintain this difference can be used to indicate the volume of air escaping through the fabric (what would be draughts in the building’s day-to-day life).
  6. We can use our equipment to identify the leakage paths. If these can be addressed relatively quickly, then we can repeat the test on the same day. In order to achieve increasingly challenging energy performance targets, air tightness requirements are becoming tighter. Typically, a good level of air tightness can still be achieved with excellent attention to detail in the decorative finish but, to achieve tighter targets, consideration must be given to air permeability within the design of the fabric, including use of membranes and tapes to maintain the air barrier – please see FAQs

The below checklists can be downloaded and used to manage air testing from design/planning, through construction to preparation for the test:

Why use ALT?

  • Helpful – we work with you to achieve the best result, identifying potential issues and repeating the testing once these have been addressed. We are on hand to answer any questions before, during and after the testing
  • Knowledgeable – we have been air testing since 2002 and all our test engineers have a vast amount of experience
  • Flexible – we try to fit in with the dates and times you need the test, we try to work around other trades to minimise disruption on site
  • Responsive – we issue quotes and certificates within 1 working day, our lead-times are typically around a week but we will try and fit you in sooner if required
  • Great value – our prices are very competitive but we can also undertake air and sound testing on the same visit to save you more money. If you do manage to find the testing cheaper, we will beat any quote.

How can we help you?

Call 01799 540220 – or send us a message

© Air Leakage Testing Limited 2020

7 Lawson Way, Aylesbury, Buckinghamshire, HP18 0UW

Tel: 01799 540220 – Email:

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