BUSINESS SUPPORT AIR TIGHTNESS
Passing an air leakage test is a regulatory requirement, says LABC Energy Consultant Jamie Best AN AIRTIGHT PLAN
Master Builder: What is the purpose of an air tightness test? Jamie Best: An air tightness test – or air leakage test – assesses air infiltration in a building’s envelope; namely, all the elements separating the indoor from the outdoor environment, including walls, windows, doors, roofs, and floors. Air leaks can significantly affect a building’s energy efficiency. Infiltration of outside air can increase energy loads, as heating systems have to work harder to maintain indoor temperatures. By identifying and addressing air leaks,
we can reduce energy consumption, utility bills and the building’s carbon footprint.
Regulations. If lucky, you can correct issues on site whilst the engineer is present. But fixing defects usually requires significant work, so a second or multiple visits are likely.
MB: Which properties require an air tightness test? JB: Since 2006, Part L of the Building Regulations has required air tightness testing of new build housing. Despite the absolute or ‘backstop’ test figures new houses need to achieve (8 m3.hr. m2 @50Pa), most air tightness test figures are derived from the as-designed SAP calculation. Older regulations required different
MB: Could you provide a checklist to help FMB
members pass their air tightness tests?
JB: Avoid short-term solutions – temporary sealing or mastic – as they will lead to problems later and aren’t acceptable in
Jamie Best
terms of Building Regulations. Factor in air tightness from the design stage to make better material choices and monitor during construction to fix problems whilst they are accessible. Think about areas of the building from outside to inside that are likely to leak, and work according to the principle that air (like water) follows the path of least resistance, which isn’t always the shortest path. If air can enter through a brick mortar joint, around an unclosed cavity and plasterboard and exit through an unsealed wall-to-floor junction, it will! You should also:
testing frequencies depending on the type of dwelling, but this is no longer the case. All units need to be tested, from sites with one unit to those with hundreds of units. MB: What are some of the common mistakes leading to a failed air tightness test? JB: Bathrooms and kitchens are the ‘go to’ areas for an engineer when a property fails an air tightness test because air typically leaks in behind dry-lined plasterboard. The entry point is usually along and under the skirting, which inevitably gets a mastic seal to fix the issue. Behind kitchen units, baths and toilets without skirting, there is usually a large cavity. Applying a continuous ribbon at all sides of dry-lining and flexible mastic behind the skirting will minimise air leakage. Be mindful of where pipe and cable distribution occurs. There is no excuse for creating a 110mm opening for a 50mm waste pipe! MB: What must be done if your property fails the test? JB: If your property fails, you need to retest to comply with Building
Set realistic air tightness targets – standard practice is now 5 m3.hr. m2@50Pa.
Engage a testing company early on – many visit for free or a nominal cost during construction to identify risk areas. Fit windows and doors properly before the test takes place. Poorly fitted windows and doors will lead to failed tests. Be mindful that the plasterboard itself won’t leak but there may be leaks where the plasterboard meets other materials. Skirtings, soil pipe risers, unsealed holes for waste pipes will leak to the outside.
Bathrooms are a common ‘problem area’ when it comes to air leakage
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Master Builder
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