When I go into homes being built before the drywall goes up, one thing I always look for is how well they did with the ceiling joists in the attached garage. I’ve written about it numerous times here in this blog. At least here in Georgia, it’s almost always done wrong unless the home builder has some guidance from a building science professional. Homes going for certification in the ENERGY STAR new homes program, for example, have to have a home energy rater on the project, so they can’t get away with the standard, sloppy method of not making a continuous air barrier.
Gallery of rogues
Here are a few of the photos I’ve taken of how to do it wrong. This first one shows no blocking and it also has a (terribly installed) flex duct running through, making it pretty much impossible to seal. (I wrote about this one in 2012.)
Then there’s this, where they’ve got the I-joists running straight across the wall separating the garage from the conditioned space.That’s not terrible because they still have time to come back and add some blocking and finish it up some air sealing. But it’s extra work that could have been avoided with a better design. (I wrote about this one in 2015.)
And finally, a masterpiece! This tortured band joist does have blocking but the only possible way to get that area air sealed is to use spray foam. And that’s fine, but I have a feeling they’re not doing that here. (I wrote about this one last month.)
Yesterday, I finally walked into a new house being built and saw the garage ceiling joists in the lead photo above. Amazing! They actually put a rim board there first and stopped the joists on the garage side, not allowing them to go all the way through. Hooray!
Then I discovered the reason why. That’s an outside wall. The wall to the conditioned space still lacks blocking.
Why does this matter?
The air quality in a typical attached garage is far worse than what’s inside the home. You don’t want that air in your home, so the first step is to make sure you have a continuous air barrier separating the garage from the living space. Then you want to not do stupid things, like putting a supply vent or two from your heating and air conditioning system into the garage. And if you really want to keep that garage air out of the house, you can install an exhaust fan to run the garage at negative pressure.
Here in Georgia, all new homes have to get a blower door test. Yet I still see this stuff all the time. Why? Because even when they totally screw up the air barrier between the garage and the house, they probably don’t have a problem passing the blower door test. (Our threshold is 7.0 ACH50.) Even if air can move easily in that floor system. The drywall in the garage may be enough to keep the air leakage low enough to pass. Ugh!
But that 2,500 square foot house could still have a couple thousand cubic feet per minute of air leakage at 50 Pascals. Which means a significant amount of air could still move from the garage to the house. And who knows what happens to the drywall in that garage after the house has been lived in a few years.
Is this just a Georgia thing? What are regular home builders doing about this detail in your area?
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