Hi Gary.
I was also state licensed in Ohio as an Inspector up to a couple of years
ago (couldn't afford the time to attend the mandatory seminars, being
out-of-state an all. Travel time killed me when I did attend.) Anyway, I
believe that Ohio is now using the IRC as the basis for its code. If you
have a copy (I don't have the current Ohio Building Code handy) it's in
section R905.2.7 of the 2003 IRC. (My *guess* is the Ohio code reads the
same in this area, but as I stated, I no longer maintain the Ohio code.)

R905.2.7 "For roof slopes from two units vertical in 12 units horizontal
(17-percent slope), up to four units vertical in 12 units horizontal
(33-percent slope), underlayment shall be two layers applied in the
following manner....." (followed by a long description of how to start the
felt, how much to lap, how to fasten, etc.)

For roofs of 4:12 or greater, a single layer is all that's required
(R905.3.3.2 "High Slope Roofs").
30# felt (along with other materials) is only required in the valleys.

There's also a reference for two layers in section R905.2.7.1 for two layers
to be cemented together for ice protection.

R905.2.7.1 "In areas where the average daily temperature in January is 25
deg. or less" .. "an ice barrier that consists of at least two layers of
underlayment cemented together, or of a self-adhering polymer modified
bitumen sheet, shall be used in lieu of normal underlayment and extend from
the eave's edge to a point at least 24in. inside the exterior wall line of
the building." So you can use either and the self-sealing is unquestionably
the better (and that's what I used on my house when I re-roofed.)

In both cases the requirement is for ASTM D226 Type I or ASTM D 4869 Type I
which is for standard shingle underlayment, or what's called 15# felt. ASTM
D 1970 is also referenced for the self-adhering underlayment.

You got me curious and looked them up in the ASTM standards to see what they
specified for weight. D226 Type I was 11.5lb./100sq.ft. min., D4869 was
8lb./100sq.ft. min. and D1970 wasn't specified. (Interesting, not even close
to 15lb./100sq.ft.)

Best,
Dennis

"Gary Lee" wrote in message
...
I'm licensed in seven (7) cities in NorthEast Ohio, and never heard of two
layers of felt.

Ice protection at eaves, two feet into the interior space, is a
requirement.
Two layers of felt would not be allowable to substitute for ASTM D 1970.
Two layers of felt does not meet standard ASTM D 1970.

Always use required materials, otherwise you will be red tagged. In this
case, it would be an ice/water guard.