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The Green Building Council of Australia has worked hard for over a decade to change the way buildings are built in this country. Their influence is significant, as a respectable portion of modern commercial buildings have participated in their process. They are always looking for new ways to push the industry forward.

Last week the GBCA published a group of proposed changes to their Green Star rating systems that could have a marked positive impact, and they invite you to provide feedback on the changes through consultation papers. This is important, but anyone interested in the changes to these credits is encouraged to communicate and collaborate with others to make their voice heard in a constructive way as soon as possible. So what changes are being proposed regarding building air tightness?

Most advanced building codes and standards recognize the importance of controlling envelope air leakage, and Green Star has now taken some bigger steps in that direction with its consultation paper on Building Air Tightness. Since the paper was released just a few days ago, there hasn’t had time yet for industry to deliver a coordinated response. The GBCA has been very open to feedback, and users of Green Star should send the GBCA their thoughts on the proposed edits. Comments are due January 27, 2017.

Projects have been able to receive credit for testing a building for air tightness for several years through an Innovation Challenge. Currently, a project can receive a point simply for testing, no matter how well or poorly the building does in the test. If a building does extremely well and reaches a set of best practice targets, the building can receive a second point. Several projects have now attempted this innovation challenge, with more on the way.

 

Green Star

Figure 1. Test of a freezer building for Green Star Innovation Challenge

Credit in Green Star for testing air tightness is now proposed for the commissioning credit, as envelope commissioning is unfortunately an oft-overlooked practice that belongs with other extremely valuable commissioning processes. There are some significant differences from the existing Innovation Challenge for Building Air Tightness that are worth pointing out.

The first is that there is now a maximum allowable envelope permeability (a measure of air leakage) where there was none before. Before, if you merely tested your building and it did poorly, you still got a point. Now, if you can test your building and prove that it does not leak more than 20 m3/hr·m2 at 50 Pascals, you will get credit.

The maximum permeability rate of 20 m3/hr·m2 may seem surprising. Building regulations in the UK won’t allow more than 10 m3/hr·m2, half of that. If a building’s final permeability truly is 20 m3/hr·m2, it must be called a poorly-built building. Furthermore, a building at that appalling leakage rate is difficult to test accurately. Still, the reality is that most buildings will easily beat this target and aim for a much lower one. Only the very worst would be near 20, and those projects would learn where the leaks are through the process of testing.

Blower door testing at the end of construction basically proves that you’ve done a good job on your building. That’s essentially what a code requirement for testing would do. It’s a pat on the back for a job well done, or a guard against a job poorly done. For compliance with a standard, a quantitative test is the only acceptable option. Likewise, to get extra points in Green Star for best practice air tightness, a quantitative test (not qualitative visual inspection) is the only acceptable way to prove that air tightness has been achieved.

Consider the two battles endlessly fought by codes and standards bodies. One battle is increasing the stringency or difficulty of standards – raising the bar over time. The other, sometimes bigger battle is merely to increase compliance with standards in the first place. If you consider the difficulties in getting buildings to comply with the building sealing requirements of the National Construction Code, you will appreciate the immensity of this challenge. The proposed Green Star credit first incentivizes the commissioning process itself, to get construction checked more often.

The credit also has the power to increase the strength of the commissioning industry. It requires that tests are done by members of the Air Infiltration and Ventilation Association of Australia (AIVAA) or the Air Tightness Testing and Measurement Association (ATTMA), two bodies full of professionals dedicated to quality testing. This is a good step in the right direction because it will help prevent gaming of the system by unqualified people claiming to be experienced testers, but it can be easily improved further.

The only test result that should be accepted is a certificate from ATTMA Lodgement, the database that all legitimate AIVAA and ATTMA tester members have access to. The service is a cheap and easy to use as a method of verification. Both major blower door software manufacturers in fact have buttons in the software to simply upload the results online. In the UK, over 100,000 tests have already been uploaded to ATTMA Lodgement in a few years of operation.

green star

Figure 2. Easy upload to ATTMA Lodgement function in air tightness testing software

It puts every test result in the same format, with the same, easy-to-verify data. The proposed Green Star credit says that “test results are required to be signed-off by the testing practitioner and main contractor.” From a contractor’s perspective, wouldn’t it be easier if they didn’t have to read and understand a different test report each time to find the data? From an ESD consultant’s perspective, wouldn't it be easier if they could verify the testing contractor they have engaged is qualified? Or if the test data they collected is of sufficient quality? The ATTMA Lodgement database was the UK industry’s answer to these questions.

One aspect of the proposed changes to the Green Star credit that might be altered are sampling rates. The credit cites ATTMA guidelines that state that very large buildings can be broken up into smaller pieces, and it suggests that a 10 per cent sample size would be sufficient for buildings larger than 5,000 square metres of envelope. While sampling for large projects is a good idea, 10 per cent may be too small of a sample unless it’s applied to a very large building. For comparison, ATTMA requires full testing of anything less than 80,000 square metres, which is 16 times bigger than the size currently suggested.

A 5,000 square metre envelope is roughly the size of a building that can be tested by a set of 10 standard blower door fans at 50 Pascals at a permeability of 20 m3/hr·m2. To simplify, that amount of equipment is a basic limit of cost-effectiveness for a simple blower door test. But sampling rates should be tiered, not a hard cutoff. For example, the way it’s currently written, for a building with a 5,100 square metre envelope, a 10 per cent sample is only 510 square metres, which is a tiny area not possibly representative of the building as a whole but requiring only one blower door fan. In contrast, a slightly smaller building of 4,900 square metres would require a whole-building test (100 per cent sample), needing 10 fans.

I suggest at least a few steps in between 10 and 100 per cent. The following table shows how many fans you would need to depressurize part of the building all at once. If you choose 10 fans as a basic level of cost-effectiveness, the size of the building guides the sampling rate.

green star

These are important but minor details. The proposed changes to the Green Star credit get a lot of things right. They provide more clarity, more stringency, and will help the testing industry and the buildings it serves grow in healthy ways.

 
  • Thanks Sean – interesting article!
    Given that the Green Star credit is not a government requirement, it would be awesome if the maximum air permeability was a rational number which reflects something "good". 20 m3/hr·m2 at 50 Pascals – as you say , a poor building – should not be something to aim for. I realise that they won't go for the Passive House Standard of .6. And I know that's hard (but not impossible) to achieve, having done it for our Superpod certified building system.
    However, 20? Really? Air tightness is such an important part of comfortable, energy saving buildings. How about 5!!!
    Fiona

    • Fiona, the passivhaus standard you refer is in litres per second, not m³ per hour.
      20m³/hr is close to your suggested 5 ls/h

  • Thanks for the update Sean. Good article, hope we keep up the momentum on this aspect of our building standards. It simply makes sense to provide better sealing and hence make it much easier to control the internal environment, reduce energy input and carbon footprint.

  • Yet another cost to clients who are already quitting building due to all the additional costs involved.

  • Rob, yes it's an extra cost. However, it ensures the quality of the building. Would you buy a new car which hadn't been through ANCAP safety test?
    It's the value that comes with the cost that counts.

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