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Air Permeability Testing

• Introduction
• Reference sources
• Guidance

Introduction

• Air permeability testing of completed buildings became a requirement of the Building Regulations in 2006. Prior to 2006 air permeability testing had generally been restricted to "whole building" tests on large retail warehouses and "laboratory" tests of mock-ups of curtain walling systems.
• Many architects have assumed that no special measures are required to comply with the Building Regulations requirements and that failing a pressure test will generally be the result of poor workmanship and not, therefore, the responsibility of the architect.
• Many contractors are now requesting that the line of the air barrier is shown on the drawings, and testing experience is showing that many types of concrete blockwork are far more air permeable than had previously been thought. These two points alone are making architects, and other construction professionals, far more aware of air permeability as a factor in the design of buildings.

Reference sources

Building Regulations

• The requirement for air permeability and pressure testing is covered in the various parts of Approved Document L. The requirements in the 2010 Edition are essentially identical to those in the 2006 Edition. The paragraph numbers below refer to the 2010 Edition.
• Approved Document L1A : The design standards are stated in paragraph 4.8.(b); the testing requirements are stated in paragraphs 5.14 to 5.23 inclusive.
• Approved Document L1B : No specific requirements for air permeability and pressure testing.
• Approved Document L2A : The design standards are stated in paragraph 4.30 (and Table 4); the testing requirements are stated in paragraphs 5.9 to 5.15 inclusive.
• Approved Document L2B : No specific requirements for air permeability and pressure testing.
• Approved Documents L1A and L2A both state: "The approved procedure for pressure testing is given in the ATTMA publication Measuring air permeability of building envelopes."
• In Approved Documents L1A and L2A, the air permeability requirements vary between 5 and 15 m³/(hr.m²) at 50Pa.

Air Tightness Testing & Measurement Association

• Read more at www.attma.org.
• A list of ATTMA members providing airtightness testing services is available from this link. The three commercial organisations listed below are all ATTMA members.
• The publication Measuring air permeability of building envelopes is available from this link.
• Paragraph 2.1 : Lists Normal and Best Practice air permeability for various building types. Specifiers should note the caveats in Guidance below.
• Paragraph 3.2 : Refers to the air barrier line being "confirmed with the client".
• Paragraph 5.2 : Refers, for Large and Complex Buildings, to the desirability of an ATTMA member "oversee(ing) the project".

Scottish Ecological Design Association

• Read more at www.seda.uk.net.
• Practical guidance, including typical construction details, commissioned by SEDA (Scottish Ecological Design Association) and funded by a Sustainable Action Grant from the Scottish Executive. All available free and well worth reading.

Commercial organisations

BRE

• Website: www.bre.co.uk.
• Publications: Good Building Guide GBG67 "Achieving airtightness" (in three parts). Probably the best general guide to practical methods of achieving airtightness in various forms of construction. All three parts may be purchased from www.brebookshop.com and are currently (May 2010) also available through the CIS service.

BSRIA

• Website: www.bsria.co.uk.
• Publications: Various free downloads requiring registration.
• Airtightness Testing. Page 6 states: “Specify the air seal line at a very early stage” and "Require air sealing detail drawings from the architect or design and build contractor."
• Airtightness Testing for New Dwellings.

HRS

• Website: www.hrsservices.co.uk.
• Publications: Various free downloads requiring registration. The "Air Sealing Information Pack" provides sound advice on achieving adequate airtightness.

Guidance

Achieving airtightness

• Curtain walling : Curtain walling is usually constructed to much more stringent air permeability levels than required by the Building Regulations. Detailing the junctions with adjoining construction, to achieve continuity of the air seal, must be considered. EPDM membranes are the most commonly-used material for forming airtight junctions.
• Any construction that includes a sheet vapour control layer : Most sheet vapour control layers will also function as an adequate air barrier, although this must be checked with the sheet supplier. It is important to ensure that all joints in the vapour control layer are well-sealed.
• Any construction with “wet” plaster, including skimmed dry-lining : "Wet" plaster generally forms an effective air barrier, although additional care is needed at junctions and penetrations. Site-applied sealants are the most common way of ensuring an airtight seal to adjoining construction, and around penetrations.
• Unplastered brickwork/blockwork : Achieving satisfactory levels of airtightness can be difficult with unplastered, unpainted, common blockwork often exceeding 10 m³/(hr.m²) at 50Pa even if well-constructed. Painting (two coats of roller-applied emulsion is normal) can provide a significant improvement.
• The BRE publication GBG67 "Achieving airtightness" (see above) is probably the best general guide to practical methods of achieving airtightness in various forms of construction.

The specifier should:

• Confirm whether airtightness testing is required : By reference to the relevant Building Regulations Approved Document (see above).
• Define the target air permeability value : Notwithstanding the range of values given in paragraph 2.1 of the ATTMA publication Measuring air permeability of building envelopes (see above), the Approved Documents specifically disallow using a value less than 5 m³/(hr.m²) at 50Pa at the design stage. Specifiers should be aware that it can be difficult to achieve the "Best Practice" values given in paragraph 2.1, and using 10 m³/(hr.m²) at 50Pa as the default value in early design calculations is highly recommended.
• Identify the air barrier line on the drawings : It is slowly becoming recognised good practice to identify the air barrier line on the drawings and many contractors will now request this information if it is not shown. These requests result, presumably, from the recommendations of the ATTMA test procedure (see above). See above for guidance on the most likely location for the air barrier in some forms of construction.
• Detail junctions, penetrations, etc. to achieve continuity of the air barrier : This will not be a major issue in many forms of construction, especially those where the vapour control layer is also functioning as the main air barrier. Indicating the air barrier line on the drawings will generally identify junctions where achieving continuity of the barrier may cause problems.
• Specify appropriate levels of workmanship : Almost all methods of achieving satisfactory airtightness depend on a high quality of workmanship, often significantly higher than might have been "traditional" practice for some forms of construction. Even fully-filling all mortar joints in common blockwork may be insufficient to reduce the air permeability below 10 m³/(hr.m²) at 50Pa. Most of the ATTMA members recommend that their services include site inspections during construction, and before any formal airtightness testing, and this can be extremely helpful in ensuring an adequate quality of workmanship.

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