Home Development 101: What is Air Pressure Testing?

For domestic developers or those working on larger projects, it’s important to get the basics right, starting with understanding the principles. This 101 guide will take you through the essentials of Air Pressure Testing and whether your project requires one.

What Is Air Tightness and Pressure Testing?

Air Testing, also called Air Permeability Testing, Air Leakage Testing, or Air Tightness Testing/Pressure Testing, is the accepted way to calculate the total amount of air a building loses due to leaks in its envelope, or fabric. The test is performed to determine the quantity of air that escapes through openings, gaps, or air leakage passages in the building envelope.

When a building is designed to limit the loss of heated air, it saves energy and money on bills. The more airtight a building is, the less heat it loses. This can contribute to a 50% decrease in environmental heat loss. It is important to have proper ventilation in an airtight building to prevent mold growth and condensation. Finding a balance between being airtight and having good ventilation is key.

Does My Development Need Air Testing?

All new UK developments have been required to undergo an Air Test since 2006. This is a part of Approved Document Part L (England and Wales) and section 6 of the technical handbook (Scotland). Part L is split in two, where Part L1A is for domestic properties and Part L2A is for commercial properties. The final Air Test is always done towards the end of construction and before the occupier moves in to meet Building Regulations/Standards.

The test results are utilized in SAP calculation for dwellings and SBEM for commercial buildings, affecting the overall energy rating. Testing on every individual property is not compulsory for large residential developments; a percentage of various dwelling types can be tested instead. All commercial properties, with an area of over 500 m2, require an Air Test for compliance, whereas properties under 500 m2 may still require an air test to meet the building’s target emission rate.

Why Building Projects Need A Test

Air Testing aims to boost the energy efficiency of new buildings and guarantee their Design Emission Rate is lower than the Target Emission Rate. The government has vowed to cut down on carbon emissions through the European Energy Performance of Buildings Directive (EPBD) and the Kyoto Agreement. Their method for addressing fuel and power conservation in buildings is Part L. This matters because the built environment is thought to generate about 50% of overall carbon emissions.

To improve a building’s energy performance, it’s important to maintain a high level of Air Tightness. This is because air leaks can result in poor energy efficiency, heat loss and cold draughts. Air Testing is necessary to make the building more environmentally friendly and to lower energy bills for occupants.

How Is The Test Carried Out

To test a building’s air tightness, an Air Tester registered with ATTMA, IATS or UKAS will use blower door testing equipment. This involves installing industrial fans to an external opening, typically a doorway, and taking pressure differential readings between the inside of the building and the outside. When depressurising, outside air will flow into the building through any cracks or openings in the envelope.

The air tightness of a building is measured by recording internal and external temperatures, barometric pressure, and wind speed. A fan, either computer-controlled or manual, is used to adjust the pressure at various speeds, and the readings are recorded. The computer then calculates the air leakage of the building to see if it meets Building Regulation requirements. For large commercial buildings, level 2 air testers can use Multi-fan blower door systems instead of Single-fan systems for better results.

The size and complexity of a building determine the level of air testing needed. There are three established levels of air testing.

  • Level 1: Air testing for single dwellings and smaller non-dwellings up to 4000 m2 gross envelope area, typically tested with a single blower door.
  • Level 2: Air testing for simple and complex buildings larger than 4000 m2 gross envelope area. This does not include large and complex high-rise (LCHR) buildings and phased handover/zonal buildings.
  • Level 3: Air testing for LCHR buildings, phased and zonal handover buildings.

The Air Permeability Index measures how much air passes through a fan in comparison to the pressure difference inside and outside of a building. It’s measured in m3h-1m-2, which is the air permeability rate per hour per square meter of envelope area. In the UK, the Maximum Air Permeability is limited to 10 m3h-1m-2.

New homes should have an Air Permeability of 5 m3h-1m-2 or less. Building control and your SAP assessor typically accept a test result between 3-5 m3h-1m-2. An Air Permeability reading of less than three m3h-1m-2 could indicate that the building needs to be more airtight. This could cause problems with condensation and mould, so it is important to have an adequate ventilation system in place.

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