Originally Posted By: Guest
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I'm assuming that it's going to be a cathedral style ceiling. There are two common ways to ways to approach the situation.
If fiberglass batts are to be used (or blown in fiberglass or cellulose) a provision to keep it away from the roof decking must be made to allow for ventilation to keep the roof cold. They make Styrofoam spacers for this purpose, or it can be site made using 1/4 plywood or some inexpensive material. A gap of an inch and a half is desirable. The vapor retarder should be toward the heated space. This method requires venting at the eave and ridge with a continuous path between them.
Another approach would be to fill the cavities w/ spray foam. Two types of foam are available, open cell and closed cell. Icynene is an open cell foam and some feel that the use of a vapor retarder is necessary with this foam, again, the retarder should on the heated side of the insulation.
Closed cell foams like some urethanes do not require the use of a vapor barrier.
Make sure your client resists the urge to use recessed lighting as it is difficult to detail properly and creates a violation in the vapor barrier and insulation.
All this applies to a home in a heating climate.