Air Tightness Testing

Our service

All new residential and commercial buildings require an Air Tightness Test under Part L of the Building Regulations. We can provide you with the certification you require and support you throughout the process.

Elmhurst energy approved airtightness scheme member Logo

Air tightness testing refers to a process to assess the extent to which air can leak out of or into a building. This measurement, helps determine the building’s energy efficiency and identify any air leakage points that may need to be sealed to improve comfort and reduce heating/cooling costs.

The test is performed using a blower door, which artificially pressurises and/or depressurises the building to measure the air permeability.

Our approach

We recognise that each project is unique and aim to keep things simple for our clients.

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Contact us about your project


We want to understand and advise you on the services that you require. New build dwellings and buildings require an air tightness test under Part L of the building regulations. The result of the test is an input into your energy assessment which could be a SAP calculation (domestic dwelling) or an SBEM calculation (commercial building).

There are other scenarios in which it is beneficial to carry out an air tightness test.

Uncontrolled air leakage diagnosis will be of interest to you when considering retrofit activities, heat pump assessments and building energy re-assessments.

Additionally, you may need to determine the air tightness of your building as part of a wider ventilation strategy.

Whatever your reason for an air tightness test, we are here to help you through the whole process.

Defining your requirements


Once we know the reason for your air tightness test, we need to dig a bit deeper to understand the type of building, its layout and construction method. This aids us with our approach to the test, allowing us to guide you to prepare for and maximise your chances of a positive air tightness test outcome.

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We’ll prepare a clearly defined quotation


Our quote will clearly define our service offering, requirements on site and terms and conditions. We will provide the quote to you in writing for your approval.

Attending site to carry out the test


With your agreement we will attend site to carry out the air tightness test. The building will be surveyed, measured and prepared by our onsite consultant. They will follow the applicable test procedure approved by the Elmhurst Airtightness Scheme of which we are a member.

Building details such as extract fans, flues and MVHR ducts are temporarily sealed, so that the air permeability of the building fabric can be tested.

Our consultant will then run the test from which your air permeability will be determined.

We don’t stop there. If required, we can pinpoint where there is uncontrolled air leakage in the building enabling you to take appropriate remedial works.

Stylist photo of a laptop and retrotec 5000 blower door system
A view of a house overloooking fields with white render walls and timber clad gable ends on a winter frosty morning

Providing certification and feedback


An Air Permeability Test certificate will be supplied on confirmation that the required standard, defined in the SAP/SBEM calculation, has been met. Your energy assessor will require evidence of this.

Of course, your air test may have been carried out for other reasons, in which case we will provide the appropriate documentation and feedback for your circumstances.

Why is Air Tightness Testing important?

1. Energy efficiency

Buildings with good levels of air tightness require less heating/cooling to maintain a comfortable temperature, reducing energy costs and carbon emissions. Poor air tightness can result in increased energy consumption for heating and cooling, as air infiltration leads to a higher energy load.

2. Building Regulations compliance

The Building Regulations under Part L require minimum air tightness levels, and air tightness testing verifies compliance with these standards.

3. Indoor air quality

Good air tightness helps prevent draughts, mould growth, and unwanted infiltration of pollutants, improving indoor air quality (alongside appropriate methods of ventilation). Uncontrolled air infiltration can allow pollutants and moisture to enter the building, leading to poor indoor air quality and potential health issues. Poor air tightness can result in moisture build up and mould growth, which can have negative impacts on indoor air quality and structural integrity.

4. Comfort

Buildings with good levels of air tightness reduce draughts and minimise temperature fluctuations, enhancing occupant comfort indoors. Poor air tightness can result in drafts, which can lead to discomfort and increased heating/cooling costs.

5. Building durability

By reducing air leakage, air tight buildings are less susceptible to moisture damage, which can impact building durability.

6. Reduce carbon emissions

Increased energy consumption due to poor air tightness can lead to higher carbon emissions.

7. Reduce construction costs

Remedying poor air tightness in buildings can be expensive, and correcting issues after construction can be even more so.

Get in touch to learn more

We will support you to find the best ventilation and air tightness strategies for your project.

Frequently asked questions

Can I have an air tightness test once I’ve moved in?2023-03-02T09:18:51+00:00

Yes, although it’s always best to aim to complete the test before you move in, just in case remedial works are required (furnishings and furniture can make these difficult).

What is the best stage in the build to carry out the air tightness test?2023-03-02T09:28:36+00:00

The best time to test is right at the end of the build after paint & decoration, but before your carpets go down and furniture goes in. This allows best access for remedial works to be carried out in the event of a test failure.

What if my building fails the air tightness test?2023-03-02T09:28:03+00:00

If your building doesn’t meet its air tightness target, it is possible to diagnose where the air leakages are. We do this by carrying out a floor walk of the building whilst the equipment is running. The air tightness test equipment generates a pressure difference from inside to outside. This results in air being pulled or pushed through any holes in the building fabric. When a negative pressure difference is generated, by simply placing your hand adjacent to an air leak, it is possible feel the draught generated by air movement through details like plumbing penetrations and skirting boards. It may be possible to carry out remedial works to fix the leaks on the day of the test, or if not a re-test at a later date may be necessary.

How long does an air tightness test take?2023-03-02T09:33:27+00:00

An air tightness test typically takes 2 to 2.5 hours, although this can be longer for larger dwellings/building with complex envelopes (the building envelope is the internal part of the building that faces the outside, such as the lowest floor, external walls and the highest ceiling).

Do I need to do anything before my air tightness test?2023-03-02T09:35:28+00:00

The dwelling/building should be complete. Other than that, you don’t need to do anything, we will prepare the building for the test, by temporarily sealing extractors, flues etc. Only certain elements are allowed to be temporarily sealed for an air test, so this should be left to the air tester on the day of the test.

What should I do if my dwelling/building is too air tight?2023-03-02T09:38:28+00:00

In the event that the result of the air test is deemed too low, for your existing ventilation provisions, it may be necessary to introduce another ventilation solution to mitigate this. We can support you with advice and guidance in this instance.

Choosing to work with Alex on our new build’s ventilation and air tightness testing was definitely the right decision for us. He professionally and articulately outlined the benefits and why the tests were required. Alex worked with us following initial poor results, in some cases, through to the delivery of results that met the requirements of the building regulations. He went above and beyond to provide a 5-star service and we would definitely recommend and use his services again in the future.

Sophie Denney, Self-Build Client

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