Choosing an airtightness strategy
An effective airtightness strategy cannot be added to a design at construction stage, it must be included from earliest point of the design. Airtightness conflicts are most effectively solved on the drawing board and least efficiently solved on the site. Choices about construction type, sequencing of works and materials selection are all intrinsic to the airtightness strategy and decisions on these matters must take account of how they will impact on the airtightness performance required.
Further guidance to airtightness in less common junctions may be obtained in BSRIA Guide 47/2013 Designing and constructing for airtightness.
Design Stage
• Simplify built form where possible.
• Define the line of the air barrier as early as possible. Mark up large scale sections with a bold coloured line.
• Consider and rationalise construction sequencing.
• Redefine the air barrier route and insulation strategy in critical areas to simplify details and avoid problems.
• Decide and specify which materials will form the air barrier. Consider:
Material air permeability
Buildability
Position within the construction
Long term durability
• Consider junction details between air barrier materials:
Practicality of forming the seals on site
Durability of the seals, tapes, etc.
• Minimise the number of service penetrations, especially through the external wall.
Consider how service penetrations will be sealed
Rationalise service routes and penetrations.
Highlight air barrier critical elements and junctions on construction drawings and apportion responsibility for sealing critical junctions.
Construction Stage
Appoint a site “air barrier manager” to coordinate and inspect the overall formation of the air barrier.
Brief the whole construction team (not just management) on the need for, and importance of, the air barrier. Inform the team of the air barrier line, the materials which will form the barrier and the critical junctions. Encourage operatives to draw attention to unforeseen difficulties.
Air barrier management will include undertaking:
• Coordination of the formation of the air barrier
• Site quality assurance
• Check and sign off of all “hidden” air barrier elements before covering up.
Review the construction as work proceeds to identify any weaknesses in the air barrier strategy / areas not previously considered and feed this information back to the design team. Establish solutions to any problems identified for appropriate approval.
Undertake airtightness tests at the earliest possible opportunity. This is typically done when the air barrier is first complete, after first-fix plumbing and electrics are installed and immediately prior to completion.
All materials and workmanship including airtightness tapes and sealants are to be proper materials fit for their intended use, supplied and installed as provided for in Technical Guidance Document D.
