The concept of being "airtight" in the context of buildings refers to how well a building's envelope –consisting of its exterior components such as walls, floors, roofs, external doors and windows – is sealed. A tightly sealed building envelope tightly minimises or even eliminates unwanted air leakage.
How does technology allow us to test and improve the airtightness in a building such as a block of flats?
First, I look at the importance of achieving airtightness.
Why is airtightness important?
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Controlled Indoor Environment: Airtight buildings experience minimal air leakage, which means that uncontrolled air movement is reduced. This helps maintain a stable indoor temperature, reduces draughts, and prevents the entry of unwanted airborne pollutants, ambient noise, and pests.
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Energy Efficiency: Airtight structures are more energy-efficient because they experience lower heat loss, reducing the need for heating and saving energy costs. This results in lower energy bills for residents, a reduced carbon footprint, and improved energy performance ratings.
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Improved Indoor Air Quality and Comfort: Airtight buildings can provide better indoor air quality and comfort. Proper ventilation systems, like Mechanical Ventilation Systems with Heat Recovery (MVHR), can be installed to introduce fresh, filtered, pre-heated or cooled air, maintaining healthy conditions and reducing pollutants and noise. For blocks of flats, air tightness prevents ingress of building services heat into the dwellings.
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Moisture Control: Airtight structures also offer better control over internal humidity levels, reducing the risk of condensation and mould-related issues. Additional features like demand control boosting functions and smart humidistats on MVHR systems can enhance moisture control.
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Fire Barrier: In most instances, the defined air barrier is also the fire barrier, thus air tightness can limit the spread of smoke and flames in a block of flats, allowing residents more time to escape safely.
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Acoustics: Lastly, it provides acoustic benefits not by reducing external noise infiltration, but instead reducing direct air pathways between flats and common areas, creating a quieter and more peaceful living environment.
Building regulations in the UK, such as Part L and Part F, provide guidelines for airtightness. The current minimum standard for new-build airtightness in England is an air permeability of 8.0 m3/(h.m2) when pressure tested at 50 Pascals. Achieving this level of airtightness is crucial for energy efficiency and comfort.
Assessing airtightness
To assess airtightness, a systematic process should be followed:
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Define the Air Barrier: Identify and define the components that form the air barrier in the building, such as floors, ceilings, walls, and doors.
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Set Target Airtightness Levels: Determine the desired level of airtightness based on building type and regulations.
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Integrate Airtightness into Strategy: Incorporate airtightness considerations into the overall ventilation and insulation strategies.
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Engage a Qualified Tester: Hire a professional and qualified Air Tightness Tester from recognised schemes like ATTMA or EAS.
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Conduct Testing: Perform air tightness tests at various stages, including baseline, midway through retrofit work for diagnostics, and upon completion for compliance. These results can be used in SAP modelling and to generate an improved EPC.
Airtightness Tech
Air-tightness can be tested using two approved methods involving specialist, high tech kit: blower door or pulse.
The blower door method is suitable for diagnostics and involves installing a fan in an external door or window, connected to a multi-channel manometer, which measures the differential pressures, both inside and outside and records flow rates through the fan. The test can take a few hours, depending on the building's size and complexity.
Pulse testing is quicker and is typically used for compliance as it does not allow for diagnostics. It uses a controlled series of bursts of compressed air to create a differential pressure and then measures the losses. The measurement is recorded at 4 Pascals, which is a lot lower than the 50 Pascals required for blower door testing.
Modern technology is enabling us to accurately test and therefore improve airtightness in a building. The tech isn’t cheap, however when in trained hands, the results will assist in improving the energy efficiency, comfort, indoor air quality of leaseholders’ homes.
George Booth is a Building Surveyor at EK Retrofit
