Compliance Services : Air Tightness Testing

Home Survey Reports have been carrying out Air Tightness Testing for clients as an integral part of the requirements linked with the design stage solutions and SAP Calculations.

We also offer our consultancy and training to site operatives covering Accredited Construction Design (ACDs) guidelines and best paractice helping acheive the high standards which are required under ever increasing Part L requirements.

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Basis for measurement

The Air Tightness Testing requirements of ATTMA for the measurement of the air permeability of buildings are generally based on BS EN Standard 13829:2001 - ‘Thermal Performance of buildings - Determination of air permeability of buildings - Fan pressurisation method’ with enhancements recommended by ATTMA.

Background - What is air leakage?

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 and the 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. Air tightness 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 then 1,000 m2.

The air tightness of the UK building stock has been proven to be poor, which leads to unnecessary ventilation heat loss but also to widespread occupant dissatisfaction.

Just to take one example from research, a comparison was made between two notionally 20,000 m3 buildings one with an air permeability of 9.3 m3.h-1.m-2 and the other with an air permeability of 23 m3/(h.m2). The infiltration heat load from the first was 861 GJ p.a and the second was 2,439 GJ p.a. These are highly significant energy differences caused by ‘holes’ being left in the building structure.
Such scenarios are no longer acceptable.

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

The Air Tightness Testing 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 utilising variable flow portable fans which are temporarily installed in a doorway, or other suitable external openings.