Air tightness testing

The various Regional Building Regulations require that buildings are designed to achieve an air permeability of not more than 103/(h.m2) at 50 Pa pressure. They also state that better standards of air permeability are technically desirable in buildings with mechanical ventilation and air conditioning.

In England, Wales and Northern Ireland the completed building envelope must be tested to confirm the rate of air permeability.

In Scotland the use of approved details and a reasonable standard of workmanship is deemed to satisfy the required minimum level of 103/(h.m2). If accredited details are not designed and built the input data in the model should be taken at 15m3/(h.m2). Entry of air permeability rates lower than 103/(h.m2) in the Building Warrant Application and in the calculation model have however to be verified by testing.

Better i.e. lower design values may be used for the SBEM compliance calculations but the completed building envelope will have to achieve the stated lower rate when tested. This includes buildings in Scotland.

The exception to mandatory air permeability testing for England, Wales and Northern Ireland is for buildings below 500m2 footprint area. For these smaller buildings where the developer chooses to avoid the need for a pressure test the calculation model will use an air permeability rating of 153/(h.m2). Compensating improvements in other areas of the building fabric and building services will be needed requiring to achieve the necessary compliance.

Click here for the EPIC Guide to the amendments to the Building Regulations.

The Air Tightness Testing and Measurement Association (ATTMA) was set up in 2004 to establish common standards and methodology for the measurement of air leakage.

EPIC recommends that air pressurisation testing is only carried out by specialist UKAS accredited ATTMA organisations with experience of building construction and practice. For a list of recommended test organisations – click here.

Pointers to compliance with minimum risk
Buildings will only comply and operate to AD-L2 if they are designed, constructed and commissioned to a high standard. Installation of the building envelope and particularly associated detailing to meet the new air tightness levels will probably be the greatest challenge and greatest risk for cladding contractors.

Detailing
EPIC manufacturers provide standard details for their panel systems complete with linear heat transmission values and which are designed for minimum air leakage. Use of these standard robust details and entry of the associated ψ-values in the calculation model is essential to achieving compliance under the new methodology.

Steelwork
Tolerances for purlins and cladding rails are often not clearly defined. Tolerances should be included in all specifications to ensure optimum air tightness at joints and details. New guidance on the Specification and Installation of secondary steelwork for metal cladding has been prepared by the Steel Construction Institute in conjunction with MCRMA and EPIC.

To view, download or order a copy click here.

Air permeability
Non-compliance due to an air permeability rate in excess of the allowed minimum default level of 103/(h.m2) will require remedial work, which is costly, difficult and affects completion dates.

An air permeability rate within the 103/(h.m2) default but greater than that used to calculate the Target Emissions Rate (TER) in the building model does not necessarily mean remedial works, but will require a recalculation using the same National Calculation Model and may result in a compliance failure if no compensating factors can be made.

Achieving good air permeability levels requires a disciplined approach to installation, especially in areas of complex detailing, together with the training of site supervisors and operatives to ensure compliance, reduce risk and ensure the building meets the regulations.

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Building regulations  |  EPIC guide to building regulations  |  Sustainability