Home > categories > Construction & Real Estate > Roofing Insulation > can i use a maximum 4" RIGID insulation to obtain an r-33 value on a commercial roof?
Question:

can i use a maximum 4" RIGID insulation to obtain an r-33 value on a commercial roof?

I do not have extra space on the roof. Roof also tapers to drains at one end of building.

Answer:

the R values, i am not sure. that white stuff is NOT Styrofoam. it is a cheap imitation. Real Styrofoam is made by DuPont, is usually a light blue, with a plastic seal coat on both sides. that thin plastic seal coat doubles the R value. what really does the insulation, is trapped air. air is actually a poor conductor of heat. the foam is actually little bubbles of air. dead air that is, air that cannot circulate and move. it works similarly to the way a down vest or coat works, it fluffs up and holds the air pockets out within a confining structure, thus retaining heat. the rigid stuff will last much longer, i can tell you that much. the white foam stuff deteriorates quickly. buy cheap, get cheap, is the general rule. you may wind up only having to do it again in a few years.
Nope. The DOW rigid insulation is an R-5/inch. So 4 inches gets you an R-20. Sorry.

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