Green Star Needs More Sensible Air Tightness Targets 3

Thursday, June 23rd, 2016
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It’s a great idea to encourage innovation by giving an incentive for best practice. But what if you set targets that are so hard that no one tries for them?

Green Star offers an Innovation Challenge for building air tightness, but the targets are so well out of reach for the current state of Australian construction that it is currently one of the least-pursued Innovation Challenges under Green Star. Changes to the credit can help drive innovation as originally intended.

The Green Building Council of Australia, to its credit, has been working on the air tightness issue for many months as it recognizes its importance. The GBCA has been receptive to suggestions for how any of the Innovation Challenge credits can adapt to, or drive, changes in the green building industry’s direction – in other words, to continue to innovate. The GBCA hopes to issue changes to the air tightness credit in the coming months, so this article is meant to provide a data-based argument for realigning the targets.

The credit design itself is intended to drive innovation.

There are two points available. The first is for simply conducting a test, which is a relatively straightforward, inexpensive, and worthwhile exercise. Many projects have either conducted the test or are planning to do so. The second point has so far proved more elusive (so much so that I don’t know if any project has successfully achieved it), awarded if a project reaches “best practice” levels of air tightness defined by Green Star. Unfortunately, Australian buildings are repeatedly shown to be far leakier than comparable construction elsewhere in the developed world.

A review of the Green Star credit can help foster the kinds of innovation needed to change the way buildings are built. Recommended changes include broadening and better defining the kinds of tests that qualify for the credit, improving quality control and reporting of results, realigning the targets for what constitutes “best practice” in Australia, and perhaps increasing the incentives for projects that truly do strive for greatness.

The Innovation Challenge currently specifies a whole-building air tightness test to receive credit. As Darren O’Dea pointed out in an article a few weeks ago, in order to do a whole-building test on a large building, you’ll need a lot of testing equipment, sometimes more than is practical or cost effective. For very large and complex buildings like hospitals with tight construction schedules and a very high cash burn rate, stopping the work site to prepare and conduct a test on the whole building at once is simply not feasible. The Innovation Challenge for these projects is not worth attempting.

Still, testing on a smaller scale can be very useful. A test done on a subsection of Queensland hospital confirmed that their other quality control measures such as testing mock-ups and inspecting rigorously had led to exemplary air tightness for that building section. Small-scale tests conducted on sections of building facades can be extremely valuable for quality control of water-proofing and air sealing measures. For apartment buildings, a sampling strategy for tests of individual apartments yields a great number of health, safety, comfort and energy efficiency benefits. Therefore, the Innovation Challenge should broaden the tests allowed to achieve the first point to encompass a wider variety of “envelope commissioning” measures.

Whole-building testing is still the gold standard for air tightness quality control, and the points for reaching best practice should still be reserved for those projects that perform them, but are the current targets realistic? They are based on recommendations from the Air Tightness Testing and Measurement Association (ATTMA) in the UK, where the building regulations for years have required blower door testing of new and renovated buildings. Green Star adopted ATTMA best practice targets for air permeability as measured by a whole-building test.

Australian construction is typically considerably leakier than UK construction according to test results collected in the commercial section of the Australian National Building Air Tightness Database. A relatively small number of tests have been completed on Australian buildings in the past six years on larger commercial buildings. The results show that very few buildings are meeting Green Star air tightness targets, even when concerted efforts are made to set and achieve them.

The table below shows summary statistics from air leakage tests on a different building types, aligned with the appropriate ATTMA category for reference. The tests encompass a range of test types, not just whole-building tests. In this data set, only two tested building sections indicate air leakage that meets ATTMA best practice targets.


When only whole-building test results are included, only one building in the database has achieved ATTMA “normal” levels of air tightness and no buildings have achieved best practice.

Efforts to reach this level of air tightness are not trivial. The one office building that reached ATTMA “normal” levels for whole-building air tightness (result 2.34 m3/hr·m2 @ 50 Pa) utilized a special vapor-permeable membrane as an air barrier, had regular construction inspections by an air tightness specialist, and performed preliminary testing on a smaller building section. These are best practice approaches to air tightness in Australia, yet they were insufficient to meet the definition of ATTMA best practice.

Even UK buildings have a hard time meeting ATTMA best practice targets. ATTMA recently provided me with a sample data from its own database. The ATTMA database regularly receives 500 or more tests results per day, around three per cent of which are for non-residential buildings. The data they provided for September 1, 2015 to April 30, 2016 includes more than 3,400 non-residential building tests.

Only five per cent of buildings in the data set meet ATTMA targets for best practice for offices (2.0 m3/hr·m2 @ 50 Pa), while only 13 per cent meet the best practice target for the catch-all “other” category (3.0 m3/hr·m2 @ 50Pa). In addition, 10 per cent of the buildings do not meet the standard set by UK building regulations for 10.0 m3/hr·m2 @ 50Pa. This data comes from a country where blower door testing (and by extension air tightness in general) has been required by law for years. No such market drivers exist in Australia.


Members of the Air Infiltration and Ventilation Association of Australia (AIVAA) report that clients who request air tightness testing to satisfy the Green Star Innovation Challenge seldom have the intention of trying for best practice targets. Presumably this is because the targets are perceived to be too difficult and costly to reach.

The cost of performing a test is small compared to the cost of truly achieving air tightness through use of better materials and techniques, training, and of full envelope commissioning for air tightness. Like other forms of commissioning, envelope commissioning encompasses a project’s whole lifespan, from inception to plans review, construction inspections, pre-functional testing, and finally functional testing at project completion.

This is why the first point for this Innovation Challenge should be awarded for building envelope commissioning (as a broader but well-defined endeavor), while a second point should be awarded for a more reasonable and simple whole-building air tightness target, for example the ATTMA “normal” target of 5.0 m3/hr·m2 for offices and “other” buildings. Paradoxically, loosening the requirements somewhat may drive innovation. There are projects that previously had only wanted to test and had no intention of changing the way they actually build. With a target in reach, they at least have an incentive to try.

It has also been suggested that an additional point or half-point be could also be awarded for meeting a best practice target, perhaps 2.0 m3/hr·m2. The net change to the Innovation Challenge would an additional point or half-point for best practice whole-building air tightness. For many projects, the enticing possibility of achieving not one but two or more Green Star points makes the nuts-and-bolts reality of attempting best practice air tightness more worthwhile.

The truth is that air tightness testing itself saves no energy. Building sealing does. Testing early, testing often, and testing appropriately helps us learn and check our work, and ultimately leads to better buildings.

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  1. Barry B.

    Another case of sustainability zealots engaging in rash overreach and impeding pragmatic efforts by industry to improve the built environment for users.

  2. Peter Tomkinson

    Does anyone stop to ask 'Is Air-tightness of ANY real value?'. As a research measure to test methodologies maybe but for most finished buildings? I doubt it.
    While in principal intended to provide complete control of air movement and supposedly energy consumption does this supposed ability translate to real energy savings or simply theoretical paper ones?
    What about IAQ, surely a far more important attribute in a living or working environment? Air tightness and IAQ can become mutually exclusive if the focus is all on energy which sadly appears to be the case with NatHERS and Star Ratings.
    So I ask again 'Is airtightness of ANY real value?' If the answer is no, or ONLY in energy terms – then ditch the measure.
    Buildings are for people AND the environment – not one OR the other.

    • Sean Maxwell

      Peter, I could go into a lengthy rebuttal but instead I will rely on the hard work done over the past 50 years by countless scientists to show that air tightness is one of the most cost-effective ways to improve indoor air quality when done properly. There is a reason that Passive House and all advanced building codes and standards have air tightness as a primary requirement – it works for buildings and it works for people. Check out for some great scientific information.