Air Tightness Testing In Scotland
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All houses leak air to some extent, this is known as uncontrolled infiltration, as opposed to ventilation
which is the controlled exchange of air from the outside to the inside of a building. There is no upper limit
on air infiltration in Scotland, however there is TER (Target Emission Rating) and DER (Dwelling Emission
Rating) which are based on CO2 emissions of a dwelling and represented as Kg/M²/Year. These ratings areused to quantify CO2 emissions so that Government CO2 reduction targets can be met. These are bothdetermined by employing SAP (Standard Assessment Procedure for energy rating). Air leakage is a majorcomponent of the SAP, when air-leakage is excessive more heat is required to heat the dwelling thus more energy is used and the carbon footprint goes up.
All domestic dwellings issued with a building warrant since October 1st 2011 are required to meet specificTER and DER targets using the SAP. A value of 7 air changes/M³/hr/M² @ 50 Pa. is set as the default in the TER for the design of dwellings, so air infiltration over this amount may result in a failing to meet the TERtargets. depending on other variables in the TER to be determined by your verifier (Building StandardsOfficer). Your dwelling may have been designed with a higher or lower air infiltration rate, the air-
tightness test verifies if the design target is met. A value of less than 5M³/hr/M² @50 Pa Can be
considered too low to maintain good air quality and additional measures may be required to assure air
quality standards are met as per regulation 3.14 of the Scottish Building Regulations.
Ultimately it is the Building Standards Officer who determines if your dwelling meets the air infiltration
rates, but the standards are there for a reason all of which benefit you. Too much infiltration and your
carbon footprint and your heating bills go up, too little air change and your air quality is poor and
unhealthy to live in. It is almost impossible to determine air change levels in a dwelling at the design stage,
because of all the variables which come into play, especially quality of construction. That's why the test is