Spray Fireproofing OK in a Return Plenum?

8/29/2022

Are there any code requirements, or restrictions, to using spray-applied cementitious fireproofing on a steel structure in the space above the ceiling of a building when it is being used as a return air plenum?

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5 Comments

Alex

8/29/2022 05:30:48 am

Hi,

IMC (2015) 6.2.2.1 states that "materials within plenums shall be noncombustible or shall be listed and labeled as having 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."

Confirm with the fire proofing used, but most fall under these limits with both the flame spread and smoke index around 10.

Thanks,
Alex

Ralph Giro

8/29/2022 09:58:58 am

I would be shocked that the EOR or Building Dept. would approve that the space above a ceiling be used as as a return air plenum. The environmental and health issues are so many. Start with insect & rodent feces.

Todd E Wyatt

8/29/2022 12:16:46 pm

Spray Applied Fireproofing (SFRM) increases the fire-resistive rating (FRR) of non-combustible building components including the primary structure. This is typically added to meet the building's Type of Construction requirements.

The adopted Mechanical Code (IMC) may include requirements for plenums used for RA but I was unable to find a reference to SFRM.

John Dalton

9/6/2022 08:07:26 am

I would make sure that the product is not a fiber-based product but always use cementitious fireproofing wherever there is a chance of air-movement across the surface.

Matthew Benson

11/9/2025 02:48:22 pm

There should be no fiberous fireproofing onstalled exsposed in any plenum that is accessable for future work. Paint or wrapped in drywall should be sufficient. Cementainpus fireproofing will kill and caise more problems than a fire its self

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Spray Fireproofing OK in a Return Plenum?

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