I’d like to beef up some insulation in a 2×6 rafter space and polyisocyanurate is the most bang/inch. I need to make a little 3″ polyiso sandwhich and the stuff I can get has foil facing. What’s the best adhesive to use to bond this stuff together?
BTW, is there a problem with having a radiant barrier in the middle of the sandwhich, i.e. =
foil facer-polyiso-foil facer : foil facer-polyiso-foil facer
where the : is the bonding agent?
Lastly, just a rant. HD stinks, in my opinion. They store their sheets of Tuff-R so badly that is all rippley and you can’t get two flat pieces.
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A radiant barrier is not a radiant barrier if it is in contact with material on both sides. An air space is required to avoid conduction through the material.
Are you cutting pieces to fit between the rafters? If so, it is very important that you seal the edges so that air can't leak around them and get to the top of the insulation. If you are putting it on the face of the rafters, it will be better to stagger your joints both directions to try to avoid the same air leakage problem.
The foil is not bonded very well on some polyiso board so if you glue it up the bond of the foil may be the weak link.
Can you tell us what you are trying to do and why? Maybe you could post a couple of pics. We might be able to make better suggestions based on our experience if we had a clearer understanding of your situation.
Hi Ray. We talked about this a bit a couple months ago in:
http://forums.taunton.com/tp-breaktime/messages?msg=60829.1 but the foam panels on the roof isn't going to work for a variety of reasons and I'm not sure the spray foam guys will be able to adequately fill these rafter bays without voids. Here's a (not too great) picture of the area in my roof I'm trying to insulate. Sorry about the flash spot, I can try and get a better one when I get home. This is the sloped part of the 2nd floor ceiling. The rafter's are 2x6s with furring strips and then rock lath for the sloped ceiling. The drawing should help. I'm in eastern massachusetts.I thought about fitting some polyiso pannels into the rafter spaces - maybe 3.5" total thickness, w/2" vent spacing (venting yet to be installed). For scale, this is about a 3' deep rafter bay, so I can't reach the bottom of it - but neither can a spray foamer. The plan might be to caulk the bottom edge of a polyiso panel and put it in the rafter bay so the caulk would seal to the top plate, 3' away. If air sealing the foam panel to the rafters is crucial I could use some squishy foam weathersripping or sill gasket on the sides. When I remove the soffit & fasica in the spring to allow for venting, I can confirm/fix the seal to the top plate. It would be a monsterous amount of work to do 50 rafter bays, but I don't think there's an alternative that doesn't have other problems/cost +$10k. Though I'm open to ideas.
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