Tight spot - much more to airtightness testing than compliance and leakage diagnostics

Author: 01/09/2017

Our Luke Smith (Principal Energy Specialist and Head of Business Development at Build Test Solutions) maintains that there's much more to airtightness testing than compliance and leakage diagnostics.

Buildings require an adequate level of ventilation to protect the fabric from moisture and maintain the health, comfort and wellbeing of occupants.

However, uncontrolled ventilation, also known as air infiltration or air leakage, can occur as a result of a discontinuous air barrier, poor quality construction and unintended gaps and cracks. Such leakage can lead to a significant reduction in energy efficiency, contributing up to 20% of the total heat losses observed in existing buildings, a figure that often increases to more than 40% in well-insulated properties. High air leakage can also lead to a reduction in the effectiveness of mechanical ventilation systems.

In 2006, a requirement for airtightness testing for new-build homes and non-domestic properties was introduced in Part L1a and L2a of the Building Regulations. The purpose of the requirement is to quantify the amount of conditioned heated or cooled air that is leaking from a building in the form of uncontrolled ventilation.

Blower-door airtightness test

The blower-door airtightness test involves temporarily mounting a fan on the external envelope of the building, sealing up intended ventilation paths and blowing air into or out of the property to create a pressure differential between the inside and the outside.

The introduction of this testing requirement has drastically improved the understanding of how to reduce unintended air leakage.

The fan is often also used to detect leaks with specially formulated smoke or a thermal imaging camera to trace the movement of air as the building is under pressure.

A significant downside, though, is that the use of a fan makes it necessary for the testing to be carried out across a pressure difference range of 20–70Pa, with regulations suggesting a 50Pa average. This is unfortunate, as the behaviour of the building – and even air itself – is very different at 50Pa when compared with its behaviour under day-to-day atmospheric pressure changes, which, at around 4Pa, are much smaller.

So while the existing blower-door fan method serves as a great stress test for the building fabric and enables air leakage to be diagnosed, the concern is that the industry has perhaps become too focused on the use of the test as a means of purely demonstrating compliance, sealing leaks with a disregard to the potential wider implications.

Regulations, the blower-door fan test method and compliance software tools such as the Standard Assessment Procedure (SAP) all fail to properly acknowledge the link between airtightness and the ventilation needs of our buildings; neither does this approach take into account actual air change rates achieved and the risks that may be present, particularly in relation to indoor air quality and overheating.

Build Test Solutions

Build Test Solutions aims to change the way we test and verify the quality and performance of buildings by working to introduce new building performance measurement tools and techniques.

Most recently BTS has worked alongside the University of Nottingham to develop the PULSE air test as a quick, easy-to-use means of testing the as-occupied air leakage characteristics of a building at 4 pascals.

The PULSE technology is a pioneering approach which releases a low-pressure pulse of air from within a building for realistic and accurate measurement of true air change rates in a matter of minutes.

The test is easily conducted at the push of a button and is non-disruptive, enabling the equipment to be used in testing occupied homes as well as in more sensitive environments such as cleanrooms and laboratories.

This article first appeared in the RICS Building Surveying Journal, July/August 2017 issue.