What Does "Build Tight and Ventilate Right" Mean?

Small holes in the building envelope are better than big holes; some fresh air is better than none

This video is an excerpt from the Building Science Fundamentals class taught by Dr. Joseph Lstibureck, P. Eng., of buildingscience.com and founder of Building Science Corporation, back in the day. This segment focuses on the metrics behind the popular slogan "Build tight and ventilate right!" Dr. Joe explains how tight is tight, and how right is right.

TRANSCRIPT:

Build tight, ventilate right. I want you to know that the Canadians have been taking credit for this phrase, but we stole it from a Swedish guy—just letting you know. I forgot his name.

Anyway, what's tight, what's right? The short answer in terms of tight is: get rid of the big holes so the small holes don't matter. Get rid of the big holes so the small holes don't matter.

Air barrier metrics

Here are what I call air barrier metrics. I'm responsible for this table, and I want to tell you where it comes from, because you need to know where these things come from so that you can smile at air barrier specification and say, gee, maybe I don't have to be anally fastidious on everything all the time.

I was a 27-year-old punk kid with a $10 million budget saying, "Define air barriers" for a Canadian program called R-2000. I didn't know, but I knew that I didn't know. So I asked one of my mentors, an old guy by the name of Gus Handegord.

Hort was one of the guys who wrote the best book on the subject. He said, "Come on, Joe, that's stupid." I said, "Professor, it's your damn money, you're asking for this." He said, "Ah, go and measure the air leakage of drywall. Get 10 sheets of drywall. I got a friend of mine, John Claude—JC—Perau. He's building apartment buildings in Edmonton out of drywall as the air barrier. We'll set the air leakage of drywall as an air barrier."

The origin of air barrier specifications

So I got seven sheets of drywall and measured them in 1982. That's where the 0.02 liters per second per square meter at 75 pascals comes from. This got adopted by the Canadian and American codes. The air leakage of drywall defines an air barrier.

LEED and the GSA wanted me to deal with assemblies and enclosures. I said we should probably baseline and measure it, but we don't have time. So I multiplied the 0.02 by 10 and got 0.2. Then I multiplied that by 10 and got 2.

There was no testing. I just took seven drywall sheets in '82 and multiplied things by 10 and 10, which became the codes. That's crazy. Well, there you go. It got adopted by LEED. You have to convert it from metric to imperial units.

The intent was always just to get rid of the big holes.

How the Army Corps of Engineers approached it

The Army Corps of Engineers talked to me and said, "Well, what should we do?" I said, "You should probably baseline your building." So they baselined and measured about a hundred of them and then figured it out.

Their number for enclosures is 1.25, as opposed to 2, because they did it correctly. I tried to tell GSA, "What you should do is probably measure what you got, see what works, what doesn't work, spend a year, figure this out."

They said, "Joe, we don't have time. Give us your best guess." I told the Army, "Hey, take time, figure it out."

The fact that their number is 1.25 and mine was a wild-ass guess at 2 makes me feel pretty good. But you shouldn't rely on a guy who's pulling a number out of his butt to change codes.

You don't understand—this is not how you should do things. We ended up this way because people were impatient and didn't have time. And I worry about the same things being repeated in other aspects of our business.

Measure, breathe, and be reasonable

You should measure things. Take a deep breath. Figure it out. And have a reasonable number of them as opposed to just bullying your way through things.