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Una Una is offline
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Default Celotex? Old roof underlayment

Una wrote:
Under the very old asphalt shingles on my house is 2 layers of 1/2 inch
sheet board, marked "Weyerhaeuser" "insulation sheathing board" "1B"
"R1.92" and "COMBUSTIBLE MAY SMOLDER OR BURN IF IGNITED" (and indeed it
does burn easily). It appears to be wood fiber composition board. It
may be 30+ years old.


Art wrote:
Celotex was a brand name that made siding and roofing stuff. I believe they
went bankrupt long ago and someone bought their name.


Sure. Weyerhaeuser is still in business, though. Anyway, my questions
are along the lines of:

What is this product called? The brand name or the general class name.
What is its R value?
Is it more flamable than what we might replace it with?
Is the product on my roof in good condition or bad condition?
Does it tend to rot? (The roof leaks, and may have done so for years.)

It is brown, except the upper surface which is black and oily. The
printed text on the upper surface is brown on the black and in places
still easy to read. The board feels rather soft and crumbles easily.

The roofer proposes to strip this stuff off completely, put on a 4 inch
insulation, put a 1/2 inch plywood or OSB decking on top of that, then
felt and shingle.

Una