My shop currently has 1’ foam boards (foil backed facing in) stapled to the rafters that the previous home owner installed as a ceiling. I want to insulate and drywall both the ceiling and walls eventually, but want to start with the ceiling. Any issues just throwing the drywall over the foam with longer screws, or should I pull it all down and install normal batts then drywall like a typical ceiling? I’m wondering if the foam board will not compress evenly and cause issues.
Drywall over foam board on ceiling
- Thread starter Rass96
- Start date
AC-WC
Well-known member
If it's already up I don't see an issue with longer screws. How much insulation do you really want/need? You should be safe to blow insulation on top of the foam for more R factor.
If people put foam down under concrete and it doesn't compress you should be OK.
If people put foam down under concrete and it doesn't compress you should be OK.
Yeah I planned to blow more in on top down the line. I will eventually add either a heat pump or mini splits so it will need more than the 1” of foam it has now. I wasn’t sure about it compressing because it’s not like the XPS stuff, I think it’s EPS. I suppose how much it compresses is likely based on how tight I sink the screws.
billconner
Well-known member
The screw will pull through long before youll see any compresion. Try a piece as a test.
That’s a good idea. Thanks.
Boogerman
Well-known member
If you pull sheetrock tight up against the foil, you will lose the insulating value of the shiny surface reflecting back in the escaping infrared, which can be substantial. It is probably worthwhile to put a layer of the wrinkled tyvek up, that will retain some of the foil insulating properties, plus the dead air space interface will add R0.5 or so to the assembly as it cuts down on the energy transfer between the sheetrock and foil surfaces. As said above, the foam won't compress at all, and the sheetrock will go up just fine as long as the screws are long enough. A little known property of Isocyanourethane foam is that it's R value goes way down when it gets cold. So, if that's what you have instead of EPS, blowing in insulation above it will make it much more effective, as it won't be against the cold outside air.
longer screws, or to ease "finding the rafters" strapping can be fastened to them and the regular screws.
I would use longer screws & skip the strapping step myself.
I would use longer screws & skip the strapping step myself.
jack stand
Well-known member
You'll drive the screws right through the dw before you distort it because it's compressing the foam.
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Innovate1
Well-known member
You might consider metal ceiling. Less work and cheaper but depends on the look you want. Don't forget ventilation chutes when you add insulation on top so you don't block the ventilation.
I'd be worried about the compression of the foam with trying to countersink the drywall screws like a few other members have mentioned.
Like Innovate has said, metal is a one and done. In my addition, I put metal over the foam and was careful not to drive the screws home, "just past" flush the slightest bit.
Like Innovate has said, metal is a one and done. In my addition, I put metal over the foam and was careful not to drive the screws home, "just past" flush the slightest bit.
sailor_lou
Active member
My previous house had a lot of cathedral ceilings and that's exactly the way the drywall was installed, over 1" of foil backed foam board, which was screwed to the rafters with fiberglass between the rafters. We lived there 27 years and had no issues in a harsh New England climate.
Innovate1
Well-known member
If you do metal I would seal around the foam before or as I am putting the metal up. Metal doesn't provide an air seal, especially around the edge J channel) like drywall does and air leakage can make it harder to heat and cool. A minor drawback to metal.
I used foil tape at the joints and screw heads... Well plastic cap screws.
I pulled the plastic caps off the nails and put drywall screws in the caps
I also put a drywall screw in the wall at the top to mark the bottom chords of the trusses. This made it easy to screw the foam board and metal up.
csp
Well-known member
The foam isn't going to compress from driving the screws. There's way too much support because of the large surface area surrounding the screw. You'll drive the screw completely through the drywall before the foam compresses in any noticable amount.
kj_mustang
Well-known member
Make sure the bottom chord rating on the rafters can handle the weight of the drywall. May be why it only had foam board up. 2' or 4' spacing on the rafters?