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General Information on Air Tightness Testing

Home energy use is responsible for 28 per cent of UK carbon dioxide emissions, while the combination of the construction process and the usage of buildings causes 50% of all carbon emissions. The Government is aiming to achieve a 60% reduction in current emission levels of greenhouse gases by 2050, and from 6 April 2006, all new buildings must comply with the requirements of the revised Part L of the Building Regulations which deals with the conservation of fuel and power approved documents L1A and L2A deal specifically with the question of air permeability and pressure testing. It is proposed that across the board increases in standards will be routinely introduced when the Building Regulations are revised again in 2011, 2016, 2021 and so on.

According to Building Regulations, buildings should be designed with adequate ventilation provision. Above this designed, or “controlled” ventilation, a further amount of uncontrolled air “infiltration” is tolerated, and this will vary according to the overall design of the building and is known as the Target Emission Rate (TER). On completion of the building, an air tightness test measures the “uncontrolled” ventilation and checked against the target emission rate, to record the actual, or Dwelling Emission Rate (DER).

Under current Building Regulations (Part L), the general minimum level for design air permeability is 10m3 per hour per m2 of the building envelope at a maintained pressure differential between inside and out of 50 PASCAL’s. This is not in fact a very large pressure differential and corresponds to the pressure exerted by a column of water 5mm high. Compared to the fact that buildings can withstand wind induced pressures of at least 500 PASCAL’s, this seems insignificant, but it is larger than wind induced pressure on a calm day, and by testing and quoting air leakage figures at 50 PASCAL’s, inaccuracies are reduced and repeatability is improved.

The building envelope is defined as floors, walls ceilings etc. that separate the internal, or conditioned space, from external, unconditioned spaces, including lift shafts and plant rooms. Conditioned spaces may be heated or cooled.

Testing must be carried out during construction of the first 25% of each new dwelling type, in order that lessons may be learnt and adjustments made to design and/or site procedures at an early stage.