Air permeability is the quantity of air flow that passes through a certain area of a fabric. This influences the thermal comfort properties of the fabric’s material. It is usually acknowledged that the air permeability of a fabric depends on its air absorbency, thus influences its openness, as for a more absorbency and permeable fabric is attained.  

If a new build has been developed, then part L of the building regulations 2010 states that you must have an air tightness test performed. This will also be required on non-domestic buildings with a gross floor area of 500m2. Part L states the value for this test would be 10, but now the government is trying to push more of an environmental footprint by reducing the CO2 emissions across all sectors. Therefore, a target of 5 would be the new value of an air tightness test. This is due to ensuring that more builds are becoming more sustainable, environmentally efficient and friendly to our environment.  

When it comes to testing and the build comes near the value of 10, it means it wouldn’t be efficient enough. The average value of an air tightness test would be just below 5, anything around this would mean the property is efficient enough, and it will pass its test, and a certificate would be awarded, but if it doesn’t achieve this, then it would fail, slowing the process to passing building regulations. The tighter the build, the more efficient it is for breathing and also saving money on heating bills. Anything that achieves below 3 would be recommended that mechanical ventilation be installed, as the dwelling may be too air tight, and could lead to moisture build up and further more damp and health issues.