Calculate 3,000 sqft with Combustible Ceiling?

3/3/2022

I have a project that consists of a concrete deck and a solid decorative wooden ceiling suspended about 1-foot below the deck. I'm trying to determine if this condition would create a combustible concealed space per Section 8.15 of NFPA 13 (2013 edition). The section touches on the construction of structural elements, but not really the construction of the ceiling itself.

Unfortunately, I have not been able to verify the supporting structure of the ceiling as is difficult to access above due to its age and level of ornate detail. I also question the feasibility of being able to protect above this ceiling for those reasons.

If the space is considered a combustible concealed space and the preference is to omit sprinklers from the space, is the course of action at that point to increase the hydraulically remote area to 3,000 sf and omit protection?

Thanks everyone!

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9 Comments

Travis Mack

3/3/2022 08:11:52 am

If sprinklers are required, you must provide them. You don't get the choice to omit or do 3000 sq ft. You follow the sections in the concealed combustible spaces criteria to determine if sprinklers are required or not.

If sprinklers are required, then provide. If sprinklers are not required, then you go to the area about the penalties and see if your omission requires the penalty to be provided.

You can't just arbitrarily omit the sprinklers and do the 3000 sq ft design area.

Wes

3/3/2022 08:20:50 am

Agreed; well said Travis. I see this "option to choose" concept floated around a lot, and I don't agree with it.

It doesn't appear (at least to me) that the intent was ever to give an "option" on whether to provide sprinklers or not. If it's required to have sprinklers, it needs sprinklers.

Julius Wanyandeh

3/4/2022 03:10:45 am

Due to the fact that the area is combustion sensitive it is only fair to install sprinklers there is no option to that.

Dan Wilder

3/3/2022 08:26:41 am

The space as you describe it does not fall under any of the scenarios within 13-13' 8.15 or the allowances within 11.2.3.1.4 (3) & (4). When ceilings are referenced, they typically are defined as non-combustible or limited combustible ceilings.

You may be able to argue filling the space with noncombustible insulation and keeping the space under the FT² or FT³ limitations as imposed in other sections but as I don't deal with this as much, interested to see others approaches.

Casey Milhorn

3/3/2022 08:34:10 am

We run into this situation fairly frequently and I've yet to run into a situation where the 3000 sqft is required. It seems very unlikely. As Travis said you usually sprinkler or you don't. However, we do have a very pro fire sprinkler fire marshal that has several old row house situations in his jurisdiction and he is pushing to have the owners electively sprinkler one by one. In many cases he allows the above ceiling areas to not be sprinklered (where the ceilings are historical/original). Damage to the building would be substantial and cost to sprinkler these areas would be prohibitive. I am definitely in favor of leaving sprinklers out if it means these buildings get retrofitted with a sprinkler system electively. When/if the times comes to renovate and remove old ceilings, the sprinkler system is there and this can be corrected at that time.

Jonathan Sullivan

3/3/2022 08:37:16 am

A practical note for this type of installation, please make sure our GC and architect have done their due diligence with your state historic preservation office (SHPO). We've run into these sort of old tongue and groove ceilings before; they are difficult to deconstruct and reconstruct, but often need to be preserved.

Glenn Berger

3/3/2022 09:28:03 am

The 1 foot between the concrete and the wood ceiling will make it difficult to get sprinklers installed in this space. I do not see in the question, about historical nature of the facility.

I would definitely have sprinklers install below the wood ceiling and have the space between the wood ceiling and the concrete deck minimize as much as possible, just enough space to run non-combustible materials above.

Jesse

3/3/2022 09:32:50 am

I'd like to know the occupancy and design criteria. I assume its a commercial building using full 13, or we wouldn't be discussing.

It may need to be protected. But the thing is, fire doesn't spread very well laterally over flat surface. Convection is the most efficient method of heat transfer and creates positive heat feedback. In the event of a fire, the convection column will mushroom at the concrete deck. You'll have some fall-down ignition" but it won't release nearly as much energy release as you'd expect. The positive heat feedback will be severely limited.

I had a project where we had something like this, albeit a small area. I was able to omit protection using this position, and the fact that in my case, I had no means of ignition. It helped that I taught that particular fire marshal in a fire cause and origin class years before, but the premise remains.

I would advise involving your AHJ and getting their opinion.

Dave

3/3/2022 12:52:26 pm

As others have correctly stated, the 3000 sf modifer come sinto play for adjacent spaces if you utilized one of the exceptions from sprinklering offered in the "Concealed Spaces Not Requiring Sprinkler Protection" section of the Installation Requirements chapter, UNLESS the condition fits one of the exceptions to the 3000 requirement listed in the Design Approaches chapter, as part of the paragraphs on the 3000 requirement. The condition has to cleanly fall within the descrition of an exeption, as well and the description of where 3000 is exempt if you want to use that. One cannot use it the other way around and calc 3000 in order to get around sprinklering a concealed space.
Wood ceilings, whether solid or slatted, or slatted with the insulation blanket on top, or the new to the scene CLT panels, are a huge challenge, and flame-spread rating alone does not get you to not sprinklering. On some projects I have been able to get the architect to go with a wood-look cement-board, but usually only at exterior overhangs.

Calculate 3,000 sqft with Combustible Ceiling?

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