Frequently Asked Questions

Over the years we have been asked many questions about air tightness testing, why it is needed and how the test itself is carried out.

Below is a list of the most frequent questions and answers to provide you with more information and a better understanding.

If you require any more advice please feel free to contact us.

Q: Why do I need an air tightness test? >>> Answer...

A: Part L1a of the Building Regulations (2006 edition) introduced a requirement for pressure testing to be carried out. A local authority is authorised to accept, as evidence that the requirements have been satisfied, a certificate to that effect by a person who is registered by the British Institute of Non-destructive Testing in respect of pressure testing fot the air tightness of buildings.

Q: Why is air tightness important? >>> Answer...

The air tightness of a building is measured by conducting a pressure test. The result is normally expressed as an ‘air permeability’ value. The air permeability value represents the amount of uncontrolled air leakage which is present because of flaws produced during the construction process, namely gaps and cracks in the buildings fabric, especially around service pipes and where building elements join.

These air leakage pathways can cause cold draughts within the dwelling, which result in occupant discomfort. These air leakage pathways are also a route for heat loss, the warm air escaping through the gaps in the building fabric. Any warm air which passes through the building fabric can also cause condensation problems if it encounters a cold element before reaching the outside.

Improving the air tightness of dwellings will contribute to achieving the Governments overall CO2 target, it also will improve occupant comfort and is likely to help reduce maintenance and condensation problems. Improving the level of air tightness in new dwellings is particularly important because ventilation and infiltration have become significant routes of heat loss. Successive revisions to building regulations and other drivers in place have dramatically improved the other building aspects such as fabric insulation and specifying efficient heating.

The overall effect being that a larger percentage of heat in a new-build dwelling is now lost as a result of excessive ventilation and infiltration, around 30-40% in a semi-detached, for example.

Air tightness is still important in existing dwellings, but becomes a lower priority, because a larger proportion of heat loss occurs through poorly insulated elements compared to new build. It is also more problematic, and sometime expensive, to improve airtightness in existing dwellings, because the gaps are often hidden and difficult to access. There is thus a range of cost effective energy efficiency measures available which would have greater impact on energy savings in most cases, such as cavity wall insulation.

Q: What is an air tightness test? >>> Answer...

A: A pressurisation test of a dwelling is carried out by installing a fan in the doorway of the principal entrance to the dwelling, sealing all flues and chimneys, and determining the air flow rate required to maintain an excess pressure of 50 pascals (Pa).

The pressurisation test should be carried out in accordance with BS EN 13929. The air permiability measured in this way is expressed in cubic metres per hour per square metre of envelope area at 50 pascals (m3/(h.m2) at 50 Pa). The envelope area of the building, or measured part of the building, is the total area of all floors, walls and ceilings bordering the internal volume subject to the test.

In order to conduct the test readings must be taken, such as temperature, humidity, external wind speed. All equipment must be calibrated prior to commissioning, and thereafter annually. Bespoke software is used to process the data and produce the test results.

Q: What level permiability should it be? >>> Answer...

A: Building Regulations state that "a reasonable limit for the design air permeability is 10m3/(h.m2) at 50 Pa", i.e. the minimum standard. The designed air permiability may be lower that this in which case the designed air permiability should be achieved. An average result would be 7m3/(h.m2) at 50 Pa, best practice would be where the building could achieve 3m3/(h.m2) at 50 Pa.

Q: When should the test be carried out? >>> Answer...

A: The building should be tested when it is complete and ready for occupation but we can provide a quote at any time ready.

Q: How many dwellings need to be tested? >>> Answer...

A: Dwellings that have adopted approved construction details - On each development, an air pressure test should be carried out on a unit of each dwelling type selected by the BCB (building control body). Most larger developments will include many dwelling types - and one of each type should be tested to confirm the robustness of the designs and the construction procedures.
Dwellings that have NOT adopted approved construction details -
air pressure tests should be carried out on each dwelling type in the development as follows :-

        4 or less   - One test of each dwelling type
       <4 less than or equal to 40    - Two tests of each dwelling type
       >40  - At least 5% of the dwelling type, if the first 5 achieve the design air permiability this can be reduced to 2%

Q: What if the dwelling fails the test? >>> Answer...

A: If satisfactory performance is not achieved, then remedial measures should be carried out on the dwelling and a new test carried out until the dwelling achieves a saticfactory result. In addition to the remedial work on a dwelling that failed an initial test, one additional dwelling of the same dwelling type should be tested, thereby increasing the overall sample size. On request Air Tech Solutions will carry out smoke detection tests and site survey to identify air leakage paths.

Q: What information is needed by you? >>> Answer...

Set of scaled drawings for the dwelling, i.e. plan, elevation and sections to enable the calculation of building envelope & building volume.
    Designed air permiability - ( a parameter within the SAP calculations)
    Source of water and electricity

Note: Building envelope and building volume calculations are required to be calculated by Air Tech Solutions, the set of drawing will be required at least 3 days prior to the scheduled test.

Q: How much does it cost? >>> Answer...

A: We will be happy to provide you with a free quote. Please complete our online form for costs.



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