Can someone tell what is now req'd under the 2007 CBC for underlayment requirements for:

3-ply built-up flat roof


5:12 concr tile roof

Chapter 15 no longer says the type of underlayment required, it only references ASTM reports which I don't have. Any help would be appreciated.


Original Post
Concrete Tile: Section 1507.3.3 - "Unless otherwise noted, required underlayment shall conform to: ASTM D 226, Type II; ASTM D 2626 or ASTM D 6380, Class M mineral-surfaced roll roofing."

Built-Up Roofing: No underlayment; just the requirements of the manufacturer for base sheets. NRCA does not list any 3-ply BUR assemblies over a nailable deck. If you want a 3-ply system on a nailable deck, it will likely be a modified bitumen roof assembly.

For base sheets, the IBC indicates ASTM D 4601 for asphalt-coated glass fiber and ASTM D 2626 for asphalt-saturated and asphalt-coated organic felt. ASTM D 4897 for vented glass mats can also be used as a base sheet.

Some manufacturers require a layer of rosin sheathing paper between the BUR base sheet and wood-plank roof decks.
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