What is Air Tight Construction?
The basic principle of airtight building is in the formation of a continuous airtight envelope to minimise air leakage. This article covers the fundamentals of air tight construction to help home owners understand what this means to their project.
Why is it important?
An airtight building doesn’t lose heat through gaps or allow incoming draughts. This means that your heating system will work more efficiently and you’ll be more comfortable in your home. You’ll also save money on your fuel bills.
How to achieve air tightness
Air tightness means cutting out unwanted air leakage. While some leaks can be so slight as to be imperceptible, even slight draughts will increase heat loss and reduce comfort levels, sometimes dramatically. Air tightness requires attention to detail for new build situations. For retrofitting it is more challenging to achieve air tightness but it is possible through the application of particular approaches and systems.
Where does air leakage happen?
Click for larger image. Source: Improving airtightness in dwellings, Energy Saving Trust, 2005
What can your designer and builder do to achieve air tightness?
The below information outlines the fundamental tasks your designer and builder should be doing to achieve air tightness. You can review this list with them, or direct them to this page to ensure that they are up to speed on how to achieve air tightness on your project. Beware of any builder who claims this doesn’t matter – because it does!
At Building Design Stage
• Simplify the 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
- 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, especially where not accessible for future remedial work.
Best practice is to minimise the number of service penetrations 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. Apportion responsibility for sealing critical junctions to specific trades.
At Construction Stage
Agree responsibility for management of air-tightness, covering coordination and inspection of 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 rather than using makeshift solutions.
Make sure your builder recognises that any worker who has a role at any stage in the development of the building fabric, ie. bricklayers, carpenters, plasterers, plumbers, electricians, glaziers, painters and decorators, floor and carpet layers, and all other variants of crafts workers listed here including operatives have a responsibility to ensure air tightness is not compromised.
All workers onsite need to know this information and be aware of the ramifications of their actions should they interfere or come in contact with the air barrier at any stage of the build process.
Air barrier management to undertake:
• Coordination of the formation of the air barrier
• Site quality assurance
• Check and sign off all “hidden” air barrier elements before covering up.
Ensure Quality Building
Make sure the construction is reviewed 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. Undertake airtightness testing at the earliest possible opportunity. Use an established pressure testing company for accurate diagnostic feedback. All materials and workmanship, including air-tightness tapes and sealants, should be supplied and completed as per guidelines in Technical Guidance Document D. ACD Section 1 2008 p.14
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