Building tight houses is a fundamental step toward energy efficiency, and figuring out how well you’ve done is actually pretty simple.
Air leakage is calculated with a blower-door test. A technician depressurizes the house with a blower sealed into a doorway and measures how much air can pass through the building envelope.
The result is typically described either as air changes per hour at a pressure difference of 50 pascals — ach50 in industry lingo — or cubic feet per minute (CFM) @ 50 pascals. Either way, air leakage becomes a known value. If the house is too leaky, the builder can take corrective steps to tighten it up.
The process isn’t intended to be onerous. But Frank Keeler, who wants to build his own house in Washington state, has concluded that the required blower-door test is enough for him to abandon the idea of building altogether, as he explains in a recent Q&A post at GreenBuildingAdvisor.
“We are building a new home ourselves,” he writes, “and are looking for a checklist to help us prepare for the blower door test.”
Requirements for the test in Washington state have only recently been enforced, he adds, and it’s proving hard to get solid advice. Moreover, costs can range from $75 an hour to thousands of dollars, depending on where you live, and there’s no telling how many tests he’ll need to pay for.
His dilemma is the subject of this week’s Q&A Spotlight.
Where to get help
General information about blower-door testing is available online. Resources include an article by GBA senior editor Martin Holladay explaining the protocol for conducting a blower-door test and the locations of common air leaks.
Another, pointed out by Robert Post, is the green-building web site Oikos, which publishes a guide to air sealing that covers everything from doors and windows to recessed lights and attic hatches.
As to the prospect of paying through the nose for the tests, David Meiland suggests Keeler contact the Washington State University Extension Energy Program. It recently handed out 40 grants statewide for the purchase of blower-door kits to relieve backlogs, and the office should be able to offer a referral.
“Anyone trying to charge thousands is way out of reach,” Meiland says. “It takes perhaps an hour to load in, set up, run the test, pack up, and leave. It takes significantly more time than that once you take into account travel time, finding leaks for unhappy failing owners and builders, follow-up phone calls from those same unhappy folks who want help, billing and getting paid, and so on,” he adds.
For builder/owners like Keeler, the situation can look intimidating. “Our government is besieged by people upset with their polices, and this is a good example,” he writes. “They are so concerned with the technical details and what constitutes the test they completely ignore the people on the ground doing the work or testing. The IRC 2009 standards are in some cases arbitrary and confusing so people just throw up their hands in frustration.”
He would like to see the state require a certified technician conduct the test, establish a maximum cost, and require that the customer get a detailed check-off list in the event the house fails to pass. “This is another government zero-sum game,” he adds. “The cost in money, gas used, and time will never pay for the gains you get from this procedure. Like it or not, people still open windows.”
What to shoot for
To win certification under Passive House requirements, a house must be very tight indeed: the threshold is 0.6 ach50. Very few new houses meet that standard.
But Meiland thinks 5 ach50 is “quite easy” to meet, and that 2 ach50 to 3 ach50 is a reasonable goal. “It seems like right now we’re in a sort of transitional period as energy code brings blower-door testing to the masses,” he says. “Once you have gone through the process of airtight details once, it’s a lot easier the second time, and more and more builders will either own the test equipment or have a sub close by who does, so all of this drama will probably fade away and people will know how to meet the targets without so much hand-wringing.”
But to Keeler, not knowing how many tests he’d have to pay for, plus the labor and materials involved in sealing leaks, seems like too much. “The uncertainty of cost is just too great,” he says. He and his wife have decided not to apply for a building permit.
“The project is scary enough without the thought of spending weeks and thousands of dollars on test after test. It’s all too much,” he writes. “This to me signals the end to the owner/builder because of the inability to budget for ramifications of unforeseen number of tests.”
Meiland thinks Keeler’s description makes the situation sound worse than it really is, and fellow owner/builder Holladay adds this: “If your budget isn’t quite large enough for a home-building project, that’s perfectly understandable. But the problem isn’t the blower-door test. After all, the blower-door test is designed to help you lower costs, because the test will result in an energy-efficient building that will save you money for years.
“Perhaps you can design and build a smaller, more affordable house. If you do, be sure to build it tight! You’ll be glad you did.”
Our expert’s opinion
GBA technical director Peter Yost had these comments:
Don’t give up yet! You can do this!
First, start with this free checklist and guidance: EPA Thermal Bypass Checklist Guide.
Next, spring for this package of GBA Thermal Bypass details.
Finally, consider this low-tech approach: Buy a really high-quality and powerful window fan, the kind that fits right into a window opening. The one I have was made by Lakewood Engineering in Chicago (no longer available) but this whole house fan made by Air King will work just as well.
After you have air-sealed (and before you have insulated, unless your insulation is an airtight type such as spray foam) while the framing cavities are all open, run this window fan (and any other exhaust fans — for example, bath fans — that you may have installed and working in the home). The fan should be blowing out the window, not in.
I will bet that the combined depressurization force of these fans will approach 30 Pascals, which would be enough for you to go around your home with a smoke stick, a Wizard stick, a stick of incense, or even just a bunch of matches, to find any air leaks left at this stage of your work. (When you see the smoke waver, you’ve pinpointed a source of infiltration.)
If you use the Thermal Bypass Checklist and the window fan, I bet that you can get your new home down to less than 4 ach50, and then some — probably more like 2 ach50.
The official blower-door test quantifies your air leakage, but any force that significantly depressurizes your home can qualitatively identify the location of any air leaks you have missed while following the thermal bypass checklist.
This way you pay for one blower-door test at the end of your air-sealing work, and you end up with a great way to cool your house (the whole-house window fan) and a really fun toy (the Wizard Stick).