What is Air Pressure Testing?

Air Pressure Testing or Air Tightness Testing is a the process of measuring the amount of air leakage from a building through uncontrolled ventilation.  A fan is used to either pressurise or depressurise the building to around 50 pascals and the result is described as the air permeability of the building.

Air pressure testing of new build dwellings is a requirement of Part L1A of the current Building Regulations to limit air leakage. This includes houses, maisonettes, bungalows and blocks of flats.

Air leakage is the uncontrolled flow of air through gaps and cracks in a building fabric, also known as infiltration or draughts.

In the UK the approved procedure for air pressure testing dwellings is ATTMA TSL1 which is based on BS EN 13829:2001 and ISO 9972:2015.

It is a requirement of Part L1A that any dwelling tested must achieve an air pressure test result (or air permeability) of less than or equal to 10m³/h/m² at a pressure differential of 50 pascals.

There are many benefits to an airtight property, such as:

• Lower Heating Costs
• Lower Carbon Emissions
• Smaller requirement for Heating and Ventilation systems
• Better comfort for occupants

Research has shown that poor air tightness in buildings can be responsible for up to 40% of heat loss.

Organisations that provide air pressure testing services should be registered as part of an approved scheme such as the Air Tightness Testing & Measurement Association (ATTMA)  or the Independent Airtightness Testing Scheme (iATS).

EPS Group are members of the iATS scheme and are therefore able to guarantee that our air pressure test certificates will be accepted by all Building Control Bodies. We cover Cambridge, the East of England and all surrounding areas.

Air Pressure Test Process

Air pressure testing in houses is undertaken by means of a fan pressurisation or depressurisation technique.  In the UK the Air Permeability of a dwelling is recorded at a pressure differential of 50 pascals between the internal and external environment.

In order to achieve this pressure a UKAS calibrated fan is temporarily placed within the the ‘building envelope’ to provide the required flow for the test. Generally the main door to the property is selected as the most suitable place to install the fan.

Our technician will prepare the house prior to running the air pressure test. This involves temporary sealing any intended ventilation points such as cooker hoods, extract fans, trickle vents to name a few.  A detailed list is provided along with our quotations to make clients aware of the process prior to the air pressure test.

Measurements of the property will be taken to ensure that the building envelope calculation is correct.  All heating and ventilation systems should be switched off for the test and all internal doors should be open.

Several environmental readings such as temperature, barometric pressure and wind speed are also recorded before and after the test to ensure that conditions are suitable for the air pressure test to take place.

During the test the technician will take  7-10 readings at various pressure differentials, which must include 50 pascals.  The process of running an air pressure test generally takes around 20 minutes and results are  available instantly.

EPS Group generally allow 2 hours to complete each air pressure test, meaning you should have plenty of time to address any unexpected problems that may arise.

Air Pressure Testing Regime

Part L1A of the current Building Regulations stipulates that air pressure testing should be carried out on three units of each dwelling type, or 50% of all instances of that dwelling type, whichever is less. If the development were flats, each block of flats would be treated as a separate development.

The dwelling(s) to be tested should be taken from the first completed batch of units of each dwelling type.

The specific dwellings making up the test sampling should be selected by the Building Control Body, in consultation with the Air Pressure Testing Technician.

For a dwelling to class as a the same’ type’as another it should have

• The same generic form, i.e detached house, end-terraced, mid-terraced, semi-detached, ground floor flat, top floor flat, bungalow etc
• Include the same number of storeys
• Have the same Design Air Permeability (Air Pressure Test Target)
• Have a similar adjacency to unheated spaces such as garages, unheated stairwells etc
• Have the same principle construction details
• Have a similar number of penetrations, for example windows & doors
• Have an envelope area that does not differ by more than 10%

To further complicate matters, you will also need to consider the Design Air Permeability that has been stipulated in the Design Stage SAP Calculations. Any dwellings that are not tested are subject to an increased result of +2 m³/h/m²  based on the average result for those that have been tested.

EPS Group can assist you through the process and help you determine the specific air pressure testing requirements for your project.

Air Pressure Test – Common Areas of Leakage in New Build Dwellings

The image shows a sample of the common problems we find when air pressure testing houses, flats, and bungalows, however this is not exhaustive.

There are several key principles for constructing an air tight building.

• Identify the air barrier at an early stage of design
• Refer to airtightness in all contracts which may impact the air barrier
• Highlight the importance of the air tightness barrier to project teams
• Select Airtight components
• Check interfaces between components
• Ensure all site workers are aware of the importance of the air barrier
• Complete regular checks on the air barrier throughout construction.
• Ensure that all works are complete prior to the final test

EPS Group will be happy to discuss any concerns that you may have prior to a test and advise on cost effective solutions.

We are also able to offer a mid-construction air pressure testing service, which can eliminate problems and an early stage through the use of smoke tests or thermal imaging.

EPS Group – The Full Package 

In addition to air pressure testing in Cambridge & the East of England EPS Group can also provide SAP Calculations and On Construction Energy Performance Certificates, meaning your part L compliance can all be dealt with under one roof.

Using EPS Group for all Part L services can be particularly helpful if you are having difficulty achieving the required air pressure test result.  It may be that our SAP Assessors  can suggest a more cost effective solution within the SAP Calculation than spending time rectifying air leakage at completion stage.

EPS Group are able to provide the following services: