Garage ceiling details
Thanks again to all contributors for GBA as an amazing resource.
We are building a budget built PGH in Tennessee (Zone 4) and I have some garage questions.
The 30×40 garage is detached and will serve as a shop and storage space for my antique motorcycles…which are mostly British and Italian and of course leak/off-gas, etc. The slab is getting R10 rigid foam underneath. The garage has three block walls and one frame wall, block walls are exterior insulated with R10 rigid foam. We’re planning to save some money and resources by reusing some old barn roofing tin from a barn that came down on the property as the ceiling for the garage. We’ll be blowing cellulose on top of this. The space will be heated/cooled/dehumidified, but minimally except when I’m in the shop working. Humidity is something I hope to control more closely though.
How much air sealing should be done in a space like this with a lot of potential for indoor air quality issues? If we do go with the barn tin ceiling, should we install a WRB or poly barrier above it and attempt to seal it? If WRB, should it face printed side up?
Any tips and advice would be greatly appreciated.
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You can't do humidity control without a decent air barrier, so if you want to dehumidify the place, a decent air barrier under the tin ceiling would be good. You could try taping the seams on the metal ceiling but I think this would not look the best.
The air barrier could be something as simple as a well detailed house wrap (doable if careful, but I would use one of the stronger commercial ones) or a layer of OSB.
Relying on air leaks for air quality is not a good idea as you never know if you are getting enough/too much, never mind the potential heat loss through air leaks. A well sealed garage is always way more comfortable to work in. Air quality is best dealt with ventilation when you are working there. You can also always install a small exhaust fan and run it while not there.
For a workshop, I would add in some high mounted operable windows or skylight. You can crack the window and the garage door open to get some nice cross ventilation. This would quickly air out the place when need say to start one of the bikes indoors.
Thanks Akos. Since the garage is a bit more “on the cheap” I’m leaning toward house wrap. I’m guessing we could just staple that directly to the trusses, tape it all up, and go over it with the ceiling tin? The wrap would face up and tape would be on the inside, but I’m guessing that would be OK.
Feel free to let shout out if there are any problems with this assembly.
I would hang the house wrap so that the seams as parallel to the rafters. This makes it much easier to tape.
I would also try to get some acoustic caulk along the perimeter and seams as well as just as backup for the tape.
For hanging it get either cap staples or if you use regular staples tape over them to avoid holes there.
Staple holes are tiny. There is practically zero air leakage through there when the staple is intact. The issue is when the house wrap is stressed (by wind) and tears off through the staple leaving a half inch slit. That's why cap staples/cap nails are recommended to prevent tear off. Inside, with a tin ceiling going up right after it, caps wouldn't really be needed. Of course you can still use them, but they're slower, more expensive, and just going to get in the way when you put up the tin.