The following piece
of advice refers to all types of roofing. Never install insulation up
against the underside of a wood roof deck. This will expedite deterioration
of the deck and cause it to weaken and warp. This will happen in about a
five to fifteen year time span depending on your geographical location. The
expenses that this will incur are: (1) Redecking your building. These
expenses will usually start at $1.50 per square foot and go up from there,
depending on the type of wood deck that you use. (2) You'll have to
reinsulate the building. Because the insulation was on the backside of the
roof deck, when the deck is torn off, the insulation will go with it. (3)
You will be reroofing the building prematurely. Insulation installed on the
underside of the deck rather than at the ceiling level will not only lead to
premature deck deterioration but also to premature roof system
deterioration. No roofing manufacturer will warrant roofing materials with
insulation installed on the backside of the deck.
Why is it detrimental? Heat absorbed by the roof system gets trapped at
the deck level. This heat will cause the decking to warp and, in the case of
plywood, the laminates used to hold the plywood layers together will fail.
If there is some information that you need that is not included in these
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