Taryn Cornell of GBCA visiting the first ATTMA Level 2 course in Australia

GBCA’s new Green Star Homes standard and update to Green Star Buildings is a big step forward in addressing building airtightness, one of the juiciest low-hanging fruits on the building performance tree. It is cheap to implement compared to other energy savings investments, it improves comfort, and it reduces interstitial condensation risk. 

Over the years, GBCA encouraged better airtightness by incentivising testing for it. Their approach has raised the profile of airtightness as an important aspect of build quality, and fostered the growth of a fledgling testing industry. Many members of the Air Tightness Testing and Measurement Association (ATTMA) owe a large body of their testing work to Green Star. 

While these were important first steps, they left room for improvement.

An arbitrarily high leakage limit was set in Green Star Design and As-Built as a ceiling not to be exceeded. Because that number became the focus, testing was often left until building completion when the best result was expected, but at that point there is almost no time or budget left to fix any problems found. 

Requirements for testing were often grouped with other commissioning steps, so by default they became the burden of an HVAC firm. These often had little knowledge of what the airtightness requirement was, and honestly had little interest in the result. The building envelope being tested was not in their scope. If there was a failure, it was usually neither their design nor their work that was to blame. 

The most common way to satisfy the Green Star requirement was to test only a tiny portion of a building, large or small. But one can’t test a single bedroom of a house, read the number, and then claim the whole house meets a Passive House standard. No one should take you seriously. 

A narrow-minded focus on a number taken out of context is counterproductive. This is especially true because there was never a hard requirement to document any leaks found during testing, or even for anyone of importance to verify that they viewed the results. 

The commissioning process is all about feedback loops to facilitate improvement, but the learning process was broken. Thus began a race to the bottom for the lowest price for testing that satisfied the Green Star language. Some poor testing resulted, and we must expect that poor buildings resulted as well. 

A big step forward with Green Star Buildings

I have been unsparing in my critique of Australia’s approach to airtightness over the years. But I must applaud the GBCA for being open to criticism and earnest in their desire to improve. With the release of their new Green Star Buildings tool, they address every one of these shortcomings. 

The new tool recognises that building envelope commissioning is a continuing process that stretches from project conception to completion. It lays out the path forward. The new Green Star Buildings tool requires airtightness to be considered from the beginning. It is now required to review the design from a big picture point of view of building airtightness. 

While some elements often get the first attention such as the cladding, the windows, and other façade elements, other less obvious parts of the building often leak far more. For example, HVAC, lighting, plumbing, and electrical penetrations to unconditioned spaces are often ignored but serious sources of envelope leakage. 

Doing a “Red Pen Test” to define the building envelope holistically – not just focusing on the shiny curtain wall assembly – is essential. Every ATTMA tester must do plan reviews for envelope calculations, so they have become experts at viewing plans for envelope continuity. They have a list of common culprits. They can tell you where they expect to see problems again. Rather than saving the test until the end, Green Star Buildings encourages you to test and inspect the project along the way. 

A whole building test will always be the gold standard, and these tests are still encouraged. But the new tool wisely takes the focus solely off the numbers and resets it on the process of learning and revision. Simpler, smaller-scale qualitative tests can also identify problems. But because a test report that no one views is hardly useful, it is now required that deficiencies are documented and acknowledged by the project team. 

To accelerate change, the new Green Star Buildings tool uses more carrots than sticks. Facing fewer penalties and armed with more tools, teams can really focus on learning and improvement. 

A huge leap forward with Green Star Homes

With the Green Star Homes standard, things are about to change in a big way. Testing for airtightness by an ATTMA tester is required for every home. Also, verification of proper ventilation function is also required. 

The airtightness numbers required – five or seven cubic meters per hour of leakage per square meter of envelope area at 50 Pascals, depending on climate zone – are not heroic. By comparison, Passive House targets are roughly ten times tougher. But that is not the point. GBCA aims to take the mass market and lead them in the right direction. The mass market is not used to testing, or even really considering, airtightness. Evaluation leads to awareness and that leads to progress. 

Data from tests will go into the secure and anonymous ATTMA Lodgement database and a Registered Certificate of Air Permeability Test will be returned. So many layers of quality control fit on this single page – from tester accreditation and good standing, to calibration of equipment, to participation in fair trade practices – an automated computerised review of more than ten points of compliance with the AS/NZS ISO 9972 test standard is instantly run. Nothing less than perfect compliance is acceptable.

Tapping a Passion for Discovery

The GBCA unlocks an untapped power from the testing industry in ATTMA. Every current member is there for the right reasons. They aren’t there to make a quick sale; the testing industry is still quite small. They are there because like me, they love the process of discovery that comes from testing and trying to understand and fix building failures. And with every test that they do, a tester takes pride in doing the next one just a bit better.

Just watch the data coming into ATTMA Lodgement Australia and be amazed. They will get better, and better, and better. Just watch. 

Sean Maxwell is a Sydney-based building envelope consultant who runs RedPenTest.com. He leads the Australia and New Zealand sections of the ATTMA Scheme.

Spinifex is an opinion column open to all, so called because it’s at the “spiky” end of sustainability. If you would like to contribute, we require 700+ words. For a more detailed brief and style guide please email: editorial@thefifthestate.com.au

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