Air leakage is the uncontrolled flow of air through gaps and cracks in the fabric of a building (sometimes referred to as infiltration or draughts). This is not to be confused with ventilation, which is the controlled flow of air into and out of the building through purpose built ventilators that is required for the comfort and safety of the occupants. Too much air leakage leads to unnecessary heat loss and discomfort to the occupants from cold draughts. The increasing need for higher energy efficiency in buildings need in future to demonstrate compliance with more stringent building regulations targets means that air tightness has become a major performance issue. The aim should be to ‘Build tight – ventilate right’. Taking this approach means that buildings cannot be too airtight, however it is essential to ensure appropriate ventilation rates are achieved through purpose built ventilation openings.
What is the impact of Air Leakage? Fabric heat losses have been driven down over many years by the various versions of the Building Regulations and there is limited return in reducing them down significantly further. Airtightness of buildings was addressed for the first time in the 2002 edition of Part L of the Building Regulations. Although air pressure testing was encouraged, it was required only for buildings greater than 1000m2. The airtightness of the UK building stock had been proven to be poor, which leads to unnecessary ventilation heat loss but also to widespread occupant dissatisfaction.
Why should we test? Gaps and cracks in the building fabric are often difficult to detect simply by visual inspection. Air leakage paths through the building fabric can be tortuous; gaps are often obscured by internal building finishes or external cladding. The only satisfactory way to show that the building fabric is reasonably airtight is to measure the leakiness of the building fabric as a whole. Air leakage is quantified as air permeability. This is the leakage of air (m3/hour) in or out of the building, per square metre of building envelope at a reference pressure of 50 pascals (m3/(h.m2)@50Pa) between the inside and outside of the building.
Measuring air leakage: Assessment of building envelope air leakage involves establishing a pressure differential across the envelope and measuring the air flow required to achieve that differential. This is normally achieved by utilizing variable flow portable fans which are temporarily installed in a doorway, or other suitable external opening.
To arrange an air pressurisation test with Energy Focus, simply call (087) 4180878.