We're using Perma "R" polystyrene panels (2") for insulation of a semi-
cathedral ceiling with roof ventilators and open soffits (cold roof).
The area being so covered will extend on both sides of the roof from
the soffits to the purlin--not to the peak. In cross-section, the
ceiling will look exactly like the letter "A" with fiberglass bats for
those horizontal rafters in the area beneath the peak between the
purlins--there is one purlin running the length, either side. We'll be
installing the panels after affixing a vapor sheild of clear 4 mil
poly over the rafters and air spaces; then the panels will be attached
with the reflective foil facing upward to the roof sheathing.

We will be attaching the panels to the rafters by first assembling
them with adhesive to pre-varnished Luan 3/16" plywood panels,
installing the two panels as one piece with brass screws--and small
brass washers if necessary.

We'll install at least two roof vents to draw cooler air from the open
screened soffits so as to ventilate the airspaces between rafters, and
in the attic space between the purlins.

Any thoughts, pro or con, cautionary considerations pertaining to fire
hazard with these materials?
--
J.

Today's quotable quote from Iranian President AhMADingBatNutJob . . .

“The United States has never entered a serious war, and has never
been
victorious.”

http://www.theatlantic.com/internati...-limits/63312/