This video is an excerpt from a Building Science Fundamentals class taught by Dr. Joe Lstiburek, founder of Building Science Corporation. In this slice, Dr. Joe talks about exactly what is 'tight' and what is 'right' win the phrase, "build tight and ventilate right." As it turns out, many things in the building code come from pulling numbers out of—well, the air.
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. Um, I forget his name anyway.
So, what's tight, what's right? The short answer, in terms of tight, is to 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 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 R2000. 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.
Handegord was one of the guys who wrote the best book of all time on the subject, and 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 had a friend of mine, John Claude (JC) Perreault, he is building apartment buildings in Edmonton out of drywall as the air barrier.
Measuring air leakage of drywall
We decided to set the air leakage of drywall as an air barrier. So, I got seven sheets of drywall and measured it in 1982. That's where the 0.02 liters per second per square meter at 75 Pascals comes from.
This was adopted by the Canadian and American codes. The air leakage of drywall defined an air barrier.
Then, you know, LEED and the GSA wanted me to deal with assemblies and enclosures. I said, "Well, we should probably baseline and measure stuff." They said, "We don't have time."
So, I multiplied the 0.02 by 10. I got 0.2, and I multiplied that by 10 and got 2. There was no testing. I just took seven sheets of drywall in '82, multiplied things by 10 and 10, and that 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.
Now, um, the Army Corps of Engineers measured it. They talked to me and said, "Well, what should we do?" I said, "Well, you should probably baseline your buildings."
So, they baselined and measured about a hundred of them and then figured out that their number for the enclosure 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've got. See what works and 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, you know, wild-ass guess at 2 makes me feel pretty good.
Importance of measuring and patience
But you shouldn't rely on a guy who's pulling a number out of his butt to change codes, right? You don't understand. This is not the way you should do things.
We ended up this way because people were impatient and didn't have time. I worry about the same things being repeated in other aspects of our business.
All right, you should measure things, take a deep breath, figure it out, and have a reasonable number as opposed to just bullying your way through things.