Part of my garage is a 14x 24 workshop that the PO build inside the garage. The ceiling is 2x4's on 24" centers with 1" foam board nailed to the bottom of the 2x4's. I'm wanting to add/insulate the ceiling. I can do 23" r19 for $60 or I can do 15" r30 for the same price but will have to run it perpendicular to the joists on top of the joints leaving an 3.5in air gap. Am I better of with the R19 directly on top of the foam board or with the r30 but on top of the joist with a 3.5in air gap?
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insulating the ceiling ?'s r19 or r30
- Thread starter mdale
- Start date
p_mori7
Well-known member
I would go with the R19 in between. Going the other way will cause the insulation to sag and possibly leave gaps.
Gary S
Well-known member
My ceiling is similar, but I insulated first and then put up the foam board. First I put up R19 blankets between the trusses. Then I put up R6 foam board to support the insulation. After that, I blew in another R15 of loose insulation above the R19 blankets to fill any gaps that might be there. This way I get a tightly sealed R40 ceiling.
mebedave
Well-known member
I'd recommend blow in fiberglass
leeklm
Well-known member
I just blew in about 15-16" of fiberglass for an R39. Stuff is lightweight and fairly clean when blowing. I actually got more "itchy" when putting batts in my wall compared to blowing the stuff. Took about 4 hrs for 1300 sqf with one guy on the hose, and another feeding the machine (two rookies I will add...)
I'd like to go blow in insulation but am afraid of the weight, I'm guessing this was built in the 70's and I've already had to nail the foam board up in places and they used 2x4's on 24"oc on a 13'-14' span so they built it not to support much weight.
Sorry I just reread and saw blow in fiberglass not cellulose. I have not done blow in fiberglass is it really that light?
Sorry I just reread and saw blow in fiberglass not cellulose. I have not done blow in fiberglass is it really that light?
I'd rather buy the batts that properly fit in between the joists.Put the R19 in and if you find it's not enough, go back over that (perpendicular)at a later time with the R30.
samert111
Well-known member
I'd like to go blow in insulation but am afraid of the weight, I'm guessing this was built in the 70's and I've already had to nail the foam board up in places and they used 2x4's on 24"oc on a 13'-14' span so they built it not to support much weight.
Sorry I just reread and saw blow in fiberglass not cellulose. I have not done blow in fiberglass is it really that light?
If you’re not going to replace the foam board with a metal or drywall ceiling then the fiberglass batts laid perpendicular to the trusses is probably your only choice. The foam board is not designed to hold up much more than its own weight I don't think and I'm not sure it's intended to be used for ceiling (horizontal) applications either (for the same reason) unless it's going to be covered with something more rigid like drywall or OSB. Alot of people still do it but every application I've ever seen done like this the foam board sags and needs to be re-nailed back up sooner or later like you've already experienced.
If you plan to replace the foam board with something intended for a ceiling application then either blown in fiberglass or cellulose is probably the better way to go. Spray foam is the best but expensive. With anything blown in you need to make sure you do not close up your truss bay openings out to the soffit vents with insulation, assuming you have soffit vents. The area above the insulation needs to breathe from the soffits to the ridge or pot vents at the roofs peak so as to not capture the heat that does escape up into there. If you have soffit vents then put baffles in each truss bay and then use about a 6" wide pc of a fiberglass batt to close off the truss openings below the baffle at the outer wall. This will keep the blown insulation from getting out into the soffit area. Then blow in your insulation to the desired depth / R-value.
Gary S
Well-known member
If you’re not going to replace the foam board with a metal or drywall ceiling then the fiberglass batts laid perpendicular to the trusses is probably your only choice. The foam board is not designed to hold up much more than its own weight I don't think and I'm not sure it's intended to be used for ceiling (horizontal) applications either (for the same reason) unless it's going to be covered with something more rigid like drywall or OSB. Alot of people still do it but every application I've ever seen done like this the foam board sags and needs to be re-nailed back up sooner or later like you've already experienced.
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It depends on what type of foam board is used. The cheap white or pink board is structurally weak. The dense foil faced isostyrene board is very strong. My ceiling has the foil faced board held up by screws and fender washers. It has been up for years and has no problem holding up 12-14" of blanket and blown insulation.
hmbemis
Well-known member
Going the other way will cause the insulation to sag and possibly leave gaps.
It sounds like this is a boxed room within a larger structure, meaning moisture control is limited to condensation issues.
In that case, what about skinning the top of the 2x4's with foam board to provide support to unfaced R30 you lay over the top of them?
R-19 at 24-inch centers and 2x4 framing *will* sag... you need to support it by re-applying the rigid board or use wire screening. If your roof/soffits are vented, code requires you have an air gap as well. For this reason, I'd stay away from a blown in product.