A building tightness test under way (blower door)

There is a clear economic case for blower door testing of building sealing to be incorporated into the National Construction Code, according to research just released by AIRAH’s new Building Physics Special Technical Working Group.

For every dollar spent on testing, between $1.80 and $2.60 in economic benefit would be returned, the Improving Australian Housing Envelope Integrity report said.

The report analyses the current performance of Australian homes and the issues that contribute to poorly performing buildings. It also lays out the methodology for correctly sealing residential dwellings.

The research is contextualised within the broader goal of encouraging performance-based outcomes and compliance that goes beyond the current visual inspection combined with NatHERS assessment via software to demonstrated performance verification.

It found that improving air tightness combined with appropriate natural ventilation strategies could result in a reduction of up to 43 per cent in latent cooling peak load in Australian capital cities, and the use of blower door verification could result in a reduction in carbon emissions of up to 33,360 tonnes a year.

The report is the first output of the new working group, which will also provide a platform for involvement in issues around air infiltration including policy advice, regulation development and “industry-leading advice.”

The new Building Physics STG aims to ensure issues around building envelopes receive the priority they deserve, AIRAH chief executive Tony Gleeson said.

“The purpose of AIRAH’s Building Physics STG is to bring building science principles, guidance and standardisation to the mainstream Australian construction industry.”

The report noted CSIRO research that showed many Australian homes are not performing as their rating predicted, and also highlighted recurrent issues around building envelope construction and integrity in relation to air leakage and moisture control.

It also found that better performance can be achieved by following the standards construction practices already within the NCC.

The use of fan pressurisation – blower door testing – as a performance based verification measure gives a builder flexibility in terms of materials and methods used to meet the requirements, the report said.

Jesse Clarke

President of the new working group, Jesse Clarke, said the members will be focusing on air-flow and moisture migration through the building enclosure, with correct integration with HVAC systems to maintain thermal performance, acoustic performance, water ingress and healthy conditions in all classes of buildings.

The report is not recommending an increase in the current stringency of NCC energy provisions.

“It is advocating the use of a performance-based method of verification to increase air sealing alignment with the current energy efficiency objectives, facilitating industry to develop performance-based solutions for existing requirements and increase productivity within the Australian construction industry,” the researchers said.

The report makes a number of key recommendations:

  • A performance target of 10 air changes an hour is implemented as a performance-based measure in parallel with acceptable construction practice in the 2019 NCC code revision
  • AS/NZS ISO 9972 is used as the standard test methodology to validate the performance
  • A performance-based benchmark is in parallel with acceptable construction practice until the 2022 building code update where performance verification becomes the only option

Read the full report