SIP Panels in Return Air Plenum

[kar108]

The International Mechanical Code Para 602.2.1 states: Materials within plenums. Except as required by Sections 602.2.1.1 through 602.2.1.6, materials within plenums shall be noncombustible or shall have a flame spread index of not more than 25 and a smoke-developed index of not more than 50 when tested in accordance with ASTM E 84 or UL 723.

I am working on a project where SIP roof panels (4-1/2" of Urethane foam is sandwiched between (2) 7/16" OSB panels) are exposed in a ceiling plenum. Article M602 requires a flame spread of 25 or less-- I checked the American Wood Council flame spread ratings and 7/16" OSB has a flame spread in the range of 86-150. (

http://www.awc.org/Publications/dca/dca1/DCA1.pdf)

Am I correct in assuming that this does not meet code and a protective covering such as gypsum wallboard (flame spread = 15) is required?

 

[stookeyfpe]

You are correct. At the end of the day, the Mechanical Code official will need confirmation that your design complies with Section 602.2.1.