Insulation, Radiant and Vapor Barriers - Foam Board in Attic
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el1179
05-18-08, 02:00 PM
Hi, I am going to add blow in insulation (cellulose) to my attic. Currently there is 3 or 4 inches of fiberglass rolls and 2 inch think rigid foam board on top of the rafters over most of the attic. This leaves a gap between the fiberglass and the foam board because the rolls do not come to the top of the rafters.
My plan is to move the foam board and add blow in insulation up to desired R-Value. Should I then put the foam board back on top? or is it better to sell or get rid of the foam board? Any advice on how I should deal with the foam board is appreciated. I am not sure why foam board was used in the first place. Thanks.
My plan is to move the foam board and add blow in insulation up to desired R-Value. Should I then put the foam board back on top? or is it better to sell or get rid of the foam board? Any advice on how I should deal with the foam board is appreciated. I am not sure why foam board was used in the first place. Thanks.
diyplank
05-20-08, 04:23 AM
Foam board might have been used for storage? Since there was loose fill insulation they might have put them up there to set boxes on?? Just an idea. I also blew in cellulose between my joists but I have a floor in the attic. I was told when I got a quote for my walls to be insulated that I needed another foot of cellulose on top of my floor.(I live in north central PA) I didn't wanna do this b/c we have a lot of storage up there. So he said to go buy the rigid blue foam board and then 1/4" plywood so we could still use it as storage.
Hope this helps. If you ever think you'll need the board keep it. It isn't cheap to go re buy. Good Luck
Hope this helps. If you ever think you'll need the board keep it. It isn't cheap to go re buy. Good Luck
jurched
05-22-08, 07:42 AM
I'm getting ready to buy 750 sq ft of 2 inch thick blue DOW foam board to nail to my rafters as I prepare to finish off the attic.
They'll be nailed over foil-backed R-13 insulation. I hope that'll bump up the value to R-20 or more, as the foam suggests a value of R-5 to the inch.
Then, I'll screw sheet rock through the foam into the rafter joists.
Is this a viable idea or will I be wasting my time?
J
They'll be nailed over foil-backed R-13 insulation. I hope that'll bump up the value to R-20 or more, as the foam suggests a value of R-5 to the inch.
Then, I'll screw sheet rock through the foam into the rafter joists.
Is this a viable idea or will I be wasting my time?
J
diyplank
05-22-08, 11:54 AM
Make sure you have those plastic things to go in between the rafters.(forget the name of them) They will provide ventilation while your insulation is there. Why not just put up fiberlass over the plastic ventaltion things?? Then put up your drywall and attach them right to your rafters? When I helped my father in law that is what he did. You'll take 2" of height off your finished attic.
jurched
05-22-08, 01:23 PM
Yes, I've been searching all over for "rafter mates" to provide adequate ventilation.
There's already fiberglass insulation between the rafters, stapled to the joists. I'll have to peel it away, shove in the rafter mates, and then nail the foam cross-wise to hold up the fiberglass. At least, that's how I imagine doing it.
Considering my brutal gas bills, I feel I can lose two inches of space on each side in exchange for a reduction in heat loss...
There's already fiberglass insulation between the rafters, stapled to the joists. I'll have to peel it away, shove in the rafter mates, and then nail the foam cross-wise to hold up the fiberglass. At least, that's how I imagine doing it.
Considering my brutal gas bills, I feel I can lose two inches of space on each side in exchange for a reduction in heat loss...
diyplank
05-22-08, 08:00 PM
Also called baffles!! I just saw it on another post. By the way I am a diy'er w/ experience w/ this stuff. Just wanted you to know that I am not a contractor! I see what you mean about the 2" and the heat bills. I paid around 2800 bucks between Oct 07 to March of 08. That is heating oil and 2 maintenance calls.
I see what yo mean about the foam holding up the fiberglass! There isn't any paper that you can staple to the rafters?? Also if its only R-13 you'll need more like you said, so that sounds good. Just make sure its ok to fasten your drywall (1/2" or 1/4") to the foam that is attached to the rafters. Just for the drywalling sake I am not sure. I have only fastened drywall to studs. I would post something in the drywall section just to be safe. I don't see that it would hurt but you don't want to get it all up and joints filled and find out that it did a lot of movng around on ya and then have to go back and do joint work again!! GOOD LUCK
I see what yo mean about the foam holding up the fiberglass! There isn't any paper that you can staple to the rafters?? Also if its only R-13 you'll need more like you said, so that sounds good. Just make sure its ok to fasten your drywall (1/2" or 1/4") to the foam that is attached to the rafters. Just for the drywalling sake I am not sure. I have only fastened drywall to studs. I would post something in the drywall section just to be safe. I don't see that it would hurt but you don't want to get it all up and joints filled and find out that it did a lot of movng around on ya and then have to go back and do joint work again!! GOOD LUCK
jurched
05-23-08, 08:06 AM
I got the baffles last night. Frankly, I don't understand how they work. Or rather, I have an idea, but don't like it, because the baffle is M-shaped, and it looks like the open space faces the decking.
That means, my insulation will be compressed between this baffle and the styrofoam-sheetrock layers, probably putting me right back where I started in terms of R-value!
Sometimes I feel like I cannot get ahead. (Just like when the gas prices rose 30% just when I gained 30% energy savings after insulating.) I suppose I should feel good that I'm not falling behind, though!
That means, my insulation will be compressed between this baffle and the styrofoam-sheetrock layers, probably putting me right back where I started in terms of R-value!
Sometimes I feel like I cannot get ahead. (Just like when the gas prices rose 30% just when I gained 30% energy savings after insulating.) I suppose I should feel good that I'm not falling behind, though!