1-Hr Rated Wood Ceiling Need Sprinklers Within?

9/4/2025

I have a mixed-use building, retail ~6250 square feet on the ground floor with residential occupancy on the 2nd and 3rd floors. The building is a mix of wood construction with bar joists, with a ceiling attached to the bottom chord of the bar joist.

These bar joists have the bottom and top chords made of wood with 1" steel tubing to create the open bar joist.

My question concerns 2016 NFPA 13, Section 8.15.1.2.4.

Can I classify these open hybrid joists as noncombustible bar joists?

The ceiling is flat without access to the space. The ceiling assembly between the retail and the 2nd floor residential is 1-hour rated.

The big question is, can we use the exception 8.15.1.2.4 and not provide sprinklers in the space above the ceiling?

If not, I was told that if the ceiling assembly was two hours that the sprinklers in the concealed space can be eliminated. I haven't been able to find this in the NYS Building and Fire Codes.

Thanks in advance.

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6 Comments

Pete H

9/4/2025 06:02:38 am

NFPA 13 (2016) 8.15.1.2.4 - Concealed spaces formed by bar joists with less than 6" between the roof or floor deck and ceiling shall not require sprinkler protection.

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I'm not really concerned about the joists combustibility (we already accept the spaces is a concealed space) but about the distance for this exception.

If it is less than 6", the exception applies.

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That said, I think you were asking about 8.15.1.2.5 Concealed spaces formed by ceilings attached directly to or within 6" of wood joist or similar solid member construction shall not require sprinkler protection.

Especially with the line "With a ceiling attached to the bottom chord of the bar joists."

Which also has the Annex note:

A.8.15.1.2.5 - Solid metal purlin construction with a wood deck is one example of similar solid member construction.

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Obviously I cannot be certain, but that sounds like the more applicable exception

Streeter

9/4/2025 10:25:40 am

I think Pete is right that 8.15.1.2.4 would apply and I think you can omit sprinkler in these spaces.

But keep in mind that when using the exceptions for omitting sprinklers in concealed spaces you must increase your remote area to 3,000sf per 11.2.3.1.5.1.

NickG

9/4/2025 12:59:14 pm

So the fact that the bar joist are open with the sheetrock attached to the bottom chord, and not a solid Joist or solid member construction. Section 8.15.1.2.4 talks about Bar Joists which there is a distinction between bar joist and wood bar joists. section 8.15.1.2.16 addresses wood bar joist which states that the sprinklers can be omitted if non-combustible Batt Insulation fills the space between the bar joists. I would prefer to consider the space as concealed space and not install the sprinklers or the Batt insulation.

Wes

9/4/2025 04:02:46 pm

Just be careful, as there are two separate concepts being floated here.

The horizontal 'assembly' can be fire-resistance-rated, as an assembly. It can carry a 1-hour separation (or more). This is for the purposes of separating two areas for passive fire protection.

The rating is an entirely independent discussion than whether sprinklers are required.

Omitting sprinklers depends upon the standard being used (NFPA 13 vs 13R vs 13D), whether the space has combustible materials (it does), whether the space is concealed (it appears to be so), and whether there's an allowance to omit sprinklers within the space.

In this case, this sounds like it's an NFPA 13, combustible concealed space; in which case Pete cited the most probable path to omit sprinklers.

Swapping 1-hour FRR with NFPA 13 rules seem related, but they're two different concepts built for two different things.

Robert Morgan

9/4/2025 04:29:27 pm

I doubt the "hybrid" joist is less than 6", also keep in mind that filling the space with non-combustible insulation is to make it a non-combustible confined space, which would not require sprinklers. There are requirements for draft stopping that may apply also. Lastly, the wood can have a 1hr. rating IF it is used as part of an assembly (fire retardant treated wood). Just using this alone does not make a rated separation. Like others have stated, this rated separation is for the R/B,M use groups, not to omit sprinklers.

Jack G

9/15/2025 06:30:27 pm

The following prohibits 13r, 13 d:
1. Area increases due to sprinklers
2.rating reductions due to separated occupants, type VA construction ,corridor walls.
3. Miscelanous-- hazardous material increases, high rise modifications, atriums,, limited area buildings, allowable area of openings, residential floor draftstopping ( if sprinklers not extended into affected areas), other group draftstopping, ball
4. VB construction is limited to 2 story for 13 d

1-Hr Rated Wood Ceiling Need Sprinklers Within?

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