Getting ready to build a 30x40 this spring and was wondering if anyone has put down attic foil , radiant barrier under the metal roofing and if so how it works? I did this in my house and my attic is way cooler in the summer heat. I used www.atticfoil.com I will be insulating , hopefully spray foam. Ive gotten several quotes for the garage and they range from 17500 to 35300 just for the building, no concrete or insulation , basically a closed in shell. Based off of quotes, spray foam might not happen.
Attic Foil under metal roof?
- Thread starter skippydoo
- Start date
driftpin
Well-known member
I'm interested to see what the input is on this. I recently got a plywood siding covered by Hardi-board 10' X 20' premanufactured building which has a vapor barrier and a metal roof. I'm unsure if using a foil-backed poly isocyanurate roof insulation is what to do, or if I need to just go with an unfaced, non-foil insulation panel? Note in the picture that the walls and ceiling are wrapped beneath the plywood sheathing with the white vapor barrier.
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My freshly built 32x48 has radiant barrier between the purlins and metal roof panels. It was installed to reduce condensation and keep the building from sweating and dripping inside.
I have read some people that say spray foam doesn't play nice with the radiant barrier, but you'd have to talk to some spray foam companies and see what they say.
Spray foam is nice, but it's pricey. My budget wouldn't allow it, so I'll have cellulose blown in to the appropriate depth.
I have read some people that say spray foam doesn't play nice with the radiant barrier, but you'd have to talk to some spray foam companies and see what they say.
Spray foam is nice, but it's pricey. My budget wouldn't allow it, so I'll have cellulose blown in to the appropriate depth.
Firebrick43
Well-known member
Radiant barriers have to have an air space to reflect into. Other wise they are WORTHLESS !
Under concrete, worthless. Directly against the roof deck, worthless on reflecting heat out but will reflect heat back in. Spray foam sprayed on it, worthless. It should be applied to the bottom of rafter for best performance or at least draped over the trusses/rafters and have some sag to create the air space.
Under concrete, worthless. Directly against the roof deck, worthless on reflecting heat out but will reflect heat back in. Spray foam sprayed on it, worthless. It should be applied to the bottom of rafter for best performance or at least draped over the trusses/rafters and have some sag to create the air space.
driftpin
Well-known member
So, is it "either 4" insulation in the rafter bays and NO foil-covered poly iso sheet goods fastened below the rafters?" or just eliminate the foil barrier on the poly-iso insulation, and place it below the ceiling rafters, if the rafter bays are insulated with 4" fiberglass?
I guess from your description, the rafter void being filled with 4" of fiberglass is not enough space for the foil backing of the poly iso rigid insulation to work properly.
I guess from your description, the rafter void being filled with 4" of fiberglass is not enough space for the foil backing of the poly iso rigid insulation to work properly.
Skippy, whos doing the building? I have a pioneer and it was closer to 12k for a 30x40.
You can see my build in the sig.
I didn't want anything touching metal anywhere, I want air to be able to circulate and dry any moisture out that gets in the cracks. Blankets in the walls and getting blown in above the metal ceiling. Plastic on walls and ceiling.
I also used white metal on the roof. The guy building it said there is about a 15 degree difference in under roof temps when using white. The outside walls are clay color, the underside of the roof is cool to the touch in the summer and the walls are hot. Just my opinion.
You can see my build in the sig.
I didn't want anything touching metal anywhere, I want air to be able to circulate and dry any moisture out that gets in the cracks. Blankets in the walls and getting blown in above the metal ceiling. Plastic on walls and ceiling.
I also used white metal on the roof. The guy building it said there is about a 15 degree difference in under roof temps when using white. The outside walls are clay color, the underside of the roof is cool to the touch in the summer and the walls are hot. Just my opinion.
I've got quotes from 15k to 38k for the 30x40x12 5 pitch, 4 windows, 1 entry door,1-12x10 garage door ,1ft overhangs all around ,and attic truss's for 16ft . Honestly I'm getting ticked off the more quotes I get. I just don't get the added cost from seeing ads for 30x40x10 for 10500. I figured the garage would be around 15-17k. My Friend had a local guy build a 28x32 with spray foam, metal walls, sheetrock ceiling , electrical work, heat , small bathroom, and concrete complete , he didn't do anything and the total was 38k