Wood stud in Air Return Plenum

[jca]

Hi-

IMC 602.2.1 says:

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.

What are the FSI and SDI for 2x wood studs?

Since 2x wood studs are allowed to be used as fire stop, can wood studs used for wall bracing, etc., be exposed in the return air plenum?

Thank you.

[Jim Katen]

Hi-

IMC 602.2.1 says:

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.

What are the FSI and SDI for 2x wood studs?

I don't know, but I'm sure that they're well above 25 & 50.

Since 2x wood studs are allowed to be used as fire stop, can wood studs used for wall bracing, etc., be exposed in the return air plenum?

Thank you.

I don't have the IMC so I can't answer the question. However, in my experience, the answer is usually clear after a careful & thorough reading of the code. Also bear in mind that just because solid wood is acceptable for use as a fire stop, it doesn't follow that it would be accpetable for use inside plenums. The concern in each situation is completely different.

- Jim Katen, Oregon

[Jim Katen]

OK, just for you, I downloaded the Cali version of the IMC.

Look at exception #1 following the section that you quoted. It says that return air plenums in dwellings are excepted from that entire section.

- Jim Katen, Oregon