Air Tightness / Air Permeability / Air Infiltration in Buildings?

Uncontrolled air leakage is one of the factors causing heat losses and high energy consumption in commercial buildings.In the past buildings were 'leaky', and much of the required ventilation was provided by the high level of air leakage. Modern building regulations however require buildings to be far more airtight. This legislative requirement for new buildings has arisen as a result to conserve fuel and power.

Uncontrolled air leakage can cause draughts, decrease the effectiveness of ventilation systems, affect controls and generally increase energy consumption.  As insulation standards improve, heat loss and gain from air infiltration and exfiltration becomes more important.

For office buildings in particular, the increase in energy consumption is linked to the demand for air conditioning.  Research by BRE shows that exfiltration of warm air can account for up to 30% of heat loss through a building’s envelope. Reduced air leakage can lead to a significant reduction in energy use and associated CO2 emissions.

Building Regulation Requirements

The building regulation requirement throughout the UK is that the air infiltration rate should not exceed 10 m3 per hour per m2 at a pressure of 50 Pa.

Air Tightness Being Acheived

The retail supermarket industry has been working for some time to improve airtightness to reduce costs. Supermarket operators that we have carried out work with are designing and building new buildings with test results varying between 1.5 and 3 m3 per m2.

Testing

One method of demonstrating compliance is for an air leakage test to be carried out in accordance with CIBSE TM 23. This method requires the building air permeability to be determined by measuring the airflow into the building using a pressurisation fan under controlled conditions. The exfiltration flow rate is measured.

Air Infiltration in EPCs

The default value for existing building EPCs ( SBEM) of 25 m3/hr m2 can be amended as follows:

1. Less than 10 m3/hr m-2 only with an accredited air pressure test result

2. 10 m3/hr m-2 – buildings > 500 m2 built to 2002 Building Regulations

3. 15 m3/hr m-2 – buildings <= 500 m2 built to 2002 Building Regulations