The first of 3 articles on technical challenges for blower door testing in Canada in 2018.
Canada has long used blower door testing to verify air leakage rates in houses, beginning with the R-2000 program way back in the late 80s. Canada General Standards Board (CGSB) CAN/CGSB-149.10-M86 (Determination of the Airtightness of Building Envelopes by the Fan Depressurization Method) was developed in 1986 (that’s what the M86 indicates). We’ve been happily using it for 30 years without a change or an update. Recently, CGSB ‘withdrew’ the standard. There are many ‘retired’ standards in building codes, and they remain valid if referenced, but the CGSB will no longer update or maintain the standard.
Thirty years is a long time for the same standard to be in place, and a lot of programs have been built around this one. CGSB is part of of NRCan’s energy modelling, and so is foundational to pretty much every performance-based program and building code that require energy evaluations.
There’s no technical flaw apparent in the old standard, but over the same 30 years, blower door testing equipment has seen a lot of improvements, including digital manometers and integrated software packages. The top 4 manufacturers no longer support CGSB. Their mathematicians say the math that CGSB relies on doesn’t work anymore with the software. I can tell you generally why this is so. What I understand:
CGGB relies on an 8-point test, going down by 5 Pa steps from 50 Pa to create a slope on a graph that gives you an average air leakage rate at 50Pa. Advances in equipment and the integrated software allow you to take a ridiculous 1,000 tests at 50 Pa within 3 minutes, giving you a much more accurate AC/H@50Pa.
This many instances for a 50 Pa pressure test has been proven to be more accurate, replicable and quicker. It’s part of a widely used standard, ANSI/ASTM E 770-2010, Standard Test for Determining Air Leakage Rate by Fan Pressurization in the US. But that’s not the whole story.
CGSB and the National Building Code
Here’s what mere mortals who are interested in the valid use of blower door test results need to know. CGSB has been withdrawn and may lead to tests being rejected. As the CHBA has noted in communications to members, referencing a withdrawn statement can make it difficult to defend results to officials and warranty programs. If CGSB was still only referenced in voluntary programs like R-2000 or EnerGuide for Houses Rating Service (ERS), ENERGY STAR® for New Homes, etc., and the ACH at 50 Pa was the only thing we cared about, it might not be so critical an issue. However, CGSB is referenced in the model National Building Code 2015. And that means that the authority having jurisdiction (AHJ), ie, your building inspector, can choose to not accept blower door test results as part of compliance with Section 9.36. ACH at 50 Pa is also not the only performance data we get from the blower door test.
The bigger issue for all the voluntary programs and performance path requirements in the NBC is this: ELA@10 Pa. According to Mark Rosen of Building Energy, Inc., the Equivalent Leakage Area is arguably the more important number for energy modelling. I’d find it hard to argue against that statement. He noted in an email exchange with me that:
“ELA@10Pa is determined by following the curve plotted through the 8 tested points down to the 10Pa mark on the graph. It is done this way because it is nearly impossible to measure anything on site at 10Pa, so the value is extrapolated. This is why NRCan and supporters of the CAN/CGSB standard place so much importance on the 8 data points — it is postulated that more points will result in a more accurate curve on the graph. The ELA@10Pa is meant to represent how leaky the house is under normal operating conditions, and has a significant impact on the energy model outputs.”
The question is this: should CGSB be resurrected, reviewed, revised, resubmitted, or is the faster path to getting an up-to-date standard in place to adopt the current ANSI/ASTM 770-2010 standard? It would still have to go through a process, but it would likely be a faster process.
But it’s not so simple as weighing how fast the process would be.
Again, Mark Rosen: “From NRCan’s point of view, the difficulty in switching to a different standard entirely is that the underlying calculations used in the CGSB standard form the basis of the Hot2000 modelling software that generates EnerGuide ratings. It is also a Canadian standard developed using real-world testing in a Canadian climate - 30 years ago.”
This is a significant problem for Canadian home construction, one that Mark flagged in a presentation at the October 2017 national Technical Research Committee (TRC) meeting of the Canadian Home Builders’ Association (CHBA) and will be dealt with through a Code Change Request (CCR). Code officials were at the TRC, and made it clear they saw the urgency of the situation.
In the meantime, what’s a person to do?
Keep on keepin’ on, I guess.
I’ll update this article when we have more details.
