Bryan Posted June 4, 2010 Report Share Posted June 4, 2010 This is a cold air return with foam insulation board used to block electrical wires in the stud cavity of a 3 year old home. Logic tells me this is not correct and the only code reference I can find is: M1601.2.1 Duct insulation materials. Duct insulation materials shall conform to the following requirements: 1. Duct coverings and linings shall have a flame-spread index not greater than 25, and a smoke-developed index not greater than 50 when tested in accordance with ASTM E 84. Specimens tested in accordance with ASTM E 84 shall be representative of the final composite material. Click to Enlarge 21.38 KB Does this apply or is there a better code reference? Bryan Quote Link to comment Share on other sites More sharing options...
genduct Posted September 21, 2010 Report Share Posted September 21, 2010 A joist or stud space (with wooden studs) can be used as return duct and you think this standard building material is worse? If that is true it certainly sounds like an inconsistency. Quote Link to comment Share on other sites More sharing options...
Marc Posted September 21, 2010 Report Share Posted September 21, 2010 I think that foam board is approved for use as sheathing but not as duct liner. Perhaps the markings on it will tell whether it has passed that standard (ASTM E 84) or not. Marc Quote Link to comment Share on other sites More sharing options...
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