insulating roof

Old 03-08-04, 12:17 PM
Thomas Foley
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insulating roof

wondering what type of insulation to use. I have 32" O.C. rafters.
I was thinking of rigid foam but, would I have to cover this with fire protection? If this is not a recomended installment, I'm wondering if fiberglass insulation comes in wider than 24" O.C. widths.
Old 03-08-04, 06:25 PM
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I am just brainstorming, here.

I assume these are rafters, not trusses.
It's not considered a good idea to directly apply insulation to the underside of a roof. You would need to allow an air gap from the eaves to the ridge. Vents at the eaves, vents on the ridge.

EPS "Styrofoam" insulation is expensive, but 1.5 lbx/cu ft density is quite rigid. I would consider using it in this situation. Urethane foam board is also a possibility.

You have an extreme span of 32" and to avoid sagging sheetrock I would suggest sheathing the underside of the rafters with a thin plywood (3/8" ?) and applying the Styrofoam sheet to that with whatever would hold it in place until you would apply sheetrock over it. Sheetrock screws are available up to about 4 inches, so you could screw through the foam board and into the plywood.

Ignore the rafter locations and follow a typical drywall fastener pattern.

For a rough idea of costs, EPS foam board is about 25 cents per square foot, per inch of thickness. Three inches of foam would be 75 cents per square foot. Add the costs of sheetrock, plywood, fasteners and finish.

You could use the wrapped batts used in pole buildings. Fiberglass batts with a plastic covering. I think it's known as MBI; metal building insulation.

Just depends on what sort of interior finish you are attempting.
Old 03-09-04, 09:19 AM
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Like Steve here out of the box. That 32 " ???? If you dont have the shingles on how about insulation on top of the roof. then the shingles?? ED
Old 03-18-04, 06:03 AM
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How about blowing insulation? leave astrip of drywall at the top for the hose to fit. The plywood is a must. I question if 3/8 is thick enough. The styro vents against uderside of roof decking is essential too.

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