What is an Air Tightness Test?
An air tightness test, also known as as permeability, leakage, pressure or blower door testing, measures how much air is leaking our of a building. This is technically known as infiltration.
Air pressure testing is a crucial step to ensuring energy efficiency and meeting building regulations, particularly for new builds, but more recently domestic retrofit.
The main building regulation which informs air tightness testing is Conservation of fuel and power: Approved Document L.
Air leakage however should not be looked at in isolation. Airtight homes have impacts on summertime overheating risk, moisture risk and ventilation.
Air Permeability Testing Process
The test, using the blower door methodology involves creating a pressure difference inside and outside the building to quantify air leakage, or infiltration – ultimately unwanted heat losses and/ or gains.
This involves installing a fan set within a temporary door, typically a canvas placed within an external doorway.
The building can be either pressurised, depressurised or both.
Other metrics such as ambient and internal temperatures, barometric pressure and static building pressure measurements are also required as part of the test.
As you can imagine the testing equipment needs to be accurate, so routine UKAS calibration and training of the operatives is a must.
Test times depend on the size of the building and environmental conditions. It can range from 10 minutes to an hour.
An alternative approved testing methodology is Pulse. You can learn more about Pulse Testing by clicking here.
Air Test Preparation
- The building should be complete and clear of all trades before the test.
- The blower door should be placed in an external door or window, free of obstructions with a nearby power supply (13amp 240V AC).
- All background ventilation, trickle vents for example, should to be in closed positions (shut).
- Any designed mechanical ventilation such as extractor fans need to be isolated and taped.
- All internal doors need to be left open throughout the duration of the test period.
- All external doors and windows need to be closed throughout the duration of the test period.
- Temporary sealing of incomplete elements of the building fabric may be necessary to facilitate the test. This will not be undertaken by test engineers. Note that this will be recorded in test reports issued subsequently, and may invalidate the test for demonstration of regulatory compliance.
Click here to find our Air Permeability Site Status Checklist covering common leakage area preparation and recommended sealing.
Pressure Measurements, Calculations and Interpretation
The test measures the air flow into or out of the building at a range of different set pressure levels. Typically 7-10 pressure levels between 25-75 Pascals are taken.
Software is used to analyse the readings and calculate the air leakage rate.
The results are expressed as an air permeability value, which indicates the amount of air leakage per hour per square metre of the building’s envelope.
Importance of Air Tightness
Reduced Heat Loss
A well-sealed building retains heat better, reducing the need for heating and cooling.
Improved Comfort
A tighter building is quieter and less draughty and temperature fluctuations resulting in greater comfort for the occupants.
Lower Energy Bills
Reduced heat loss translates to lower heating and cooling costs.
Compliance with Regulations
Passing the air leakage testing ensures the building meets the required standards and can obtain compliance, facilitate the generation of an energy performance certificate, and in existing buildings, drive to decarbonise.
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