I have a combustible attic framed with standard wood truss framing. There are dormers that are framed on top of the roof sheathing, that have small 2-ft x 2-ft openings in the sheathing to access the dormer and provide ventilation for the dormers. Both the attic and the dormers are fully protected by the dry system.
My hydraulic calculation area is 2,535 sqft, which is increased for slope and for it being dry. A dormer falls within my remote area. My understanding is that the dormer is considered a combustible concealed space per NFPA 13-2019. The small opening of 2-ft x 2-ft is allowed under NFPA 13 Section 3.3.195. Therefore, the dormer space should not be included in the hydraulic calculations, under NFPA 13-2019 Section 23.4.4.6.5. I am being instructed by an engineer that this area is not qualifying as a concealed space and the additional sprinklers in the dormer need to be included in the hydraulic calculations. Adding the additional 8 sprinkler for the dormer to the already-calculated 34 sprinklers in the attic is causing the possibility of now needing a fire pump. Am I wrong here? Do the dormers need to be included in the remote area for this hydraulic calculation? Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
7 Comments
Pete H
10/27/2021 06:55:14 am
By code compliance, I'd say you're right. You have excellent references that show the dormer to be a combustible concealed space and the access panel (provided there aren't a bunch of them in each dormer) doesn't seem to void it being considered that.
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JFP
10/27/2021 08:32:50 am
Completely agree with Pete H on this. If the EOR's concern is the small 2x2 opening then have the GC put in an access door or hatch. You could also run a calc for just the dormer to show that it works as a separate fire area. The other option is to include the 8 heads of the dormer but reduce the area of the main calc. If you're calculating two areas on top of each other then you should be able to count that floor area twice as part of the 2535.
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Casey Milhorn
10/27/2021 08:34:56 am
Pete nailed it. You do NOT calc both levels of sprinklers in an instance like this. If you are a member of AFSA or NFSA, get an informal interpretation as well to back your statement up. I would definitely fight this one and submit for a change order. Money tends to get everyone's attention very quickly.
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Jessica Lutz
10/27/2021 09:18:05 am
I agree fully with Pete and Casey...
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Jack G
10/27/2021 10:35:29 am
Unfortunately, code officials, code compliance, sprinkler designers , are not the ones going to the fire to extinguish it.
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Jesse
10/27/2021 11:22:31 am
I agree. I'd fight this one.
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Alex
10/28/2021 08:09:44 am
I agree. I would say that the dormer does not need to be calculated. Is this a new system where you could simply upsize your distribution piping rather than adding a pump? I would push to have that CO on the engineer for requiring a system above the code and not properly covered or conveyed on Tier I drawings.
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