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Over-rafter insulation (warm roof construction)

Does anyone know the building codes for over-rafter insulation? All I can find is stuff from the UK, which is not too helpful.

We have a 1900s brick construction home in Denver that gets a lot of sun, and the upstairs converted attic gets really hot during the day. We are getting to the point of needing to do a tear-off for this roof and there is already fiberglass insulation between the rafters so we would like to find a way to lower heat gain during the summer and heat loss during the winter. We do not have any ventilation for the roof currently.

I've read a little bit about over-rafter insulation, or warm roofs, but everything says shake or slate on top.

Ok, now the question:
Can I do this legally in the US? in Colorado? Can I put composite shingles over it? Does anyone have any experience with this type of insulation? Thanks.

Timothy Miller
Re: Over-rafter insulation (warm roof construction)

Howdy, you can install a cold roof+ 1"by4" boards are nailed vertically to the roof decking then plywood then re shingle. The air space you created vents and cools the roof and atiic below. Re shingling with continuous ridge cap vents. What color are your shingles ? White is coolest black is darn hot. Your rafter bays should other wise have 2" of air space above the insulation and each rafter bay soffit vented so the heat is not radiated into the ceiling and the moisture can escape the building.

Re: Over-rafter insulation (warm roof construction)

Nailable roof deck is available from a bunch of different companies. Here are some examples. http://www.atlasroofing.com/commercial/nailbase.asp
It also can have a vented outer layer, which is required by most asphalt shingle mfgrs. for a warranty.
It's not paticuarly cheap, but I've used it in commercial construction many times in order to insulate above the structure usually so the structure can be left exposed.
Venting isn't required on metal roofs, but is still desirable.
I think a vented insulated deck could solve your problem. Their will be issues with detailing the facsia and venting. A vented drip edge along with a ridge vent works well.
Thicker polystyrene will be cheaper than thinner polyiso of the same R value usually.

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