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Good Morning. I was directed to your site through HGTV chat room. I have a question about vaulting a ceiling. I have an older home, small and want to open the ceiling up to give the appearance of a bigger room. The rafters are 24″OC with 2×12 lumber for roof sheathing. I just want to open it up, not do any mods to the existing rafters, just prime and paint the underside of the roof and the rafters leaving the joists alone. My question is about placing the insulation on the exterior of the roof. I plan on re-roofing anyway, can I lay sheets of rigid insulation, framed by laying say, 2×6’s edgewise on the rafter lines and just put new sheating and roofing materials over this? I have seen something like that on home again, but that was new construction. Any thoughts?
Brian
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I am not a pro, maybe shouldn't even be replying. A guy in town who does alot of skylights etc. swears by putting SIP's in as roof decks. He'll do a tear-off, lay up the SIP, then pop the skylights through the SIP. Re-roof and the job is done. Insulation, Deck, and shingles all in one sweep. This may work for you depending on a few factors. I'll let the pro's come up with the real answers this is just a suggestion.
*Murph, more info needed, where is this place, snow, ice, cold??
*It is located in northern iowa so yes, it is cold, snow etc. It is a seasonal home, some light usage in the winter, but primarily a summer lake home.
*Murph, I have done the following several times with good results.Strip off all the old shingles, everything down to the bare sheathing.Then I laid down two layers of 1 inch thick foil faced styrofoam, stagger the joints in both directions. Tape the seams with foil tape. Next I used full length 2x4's as sleepers laid down 3 1/2 in. side flat on the foam. I screwed the sleepers to the existing rafters with long timber screws. Do not use nails since they will not draw the sleepers tight to the foam. The sleeper are wide enough so there is no risk of them compressing the foam.Sheat the sleepers with OSB or plywood and shingle as usual, the air space created by the sleepers will vent the roof, use eve and ridge vents.Depending on the R factor you want you can increase the thickness of the foam. I have used as many as 4, 1 inch thick panels staggering the joints each time.One of these roofs mentioned is 20 years old and has shown no problems.