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Can the Quick Response Reduction be used for an above-ceiling calculation for upright heads in an interstitial combustible space?
The combustible roof deck is approximately 13'-0 above the finish floor with a ceiling of 9'-0" below. Assuming the space from the roof deck to the ceiling is 4'-0", this allows a maximum 40% reduction. Or does the calculation need to go to the finished floor for a -3 x 13/2 + 55 for a 35.5% reduction? Which is correct? Is the ceiling, in this case, the floor with only 4'-0" elevation for applying the reduction in the interstitial space, allowing the full 40% reduction? Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
5 Comments
Dan Wilder
2/25/2025 06:49:19 am
Yes to the full 40% as the space below is treated separately with pendents, provided that you are not required to use a sprinkler specifically listed for a combustible concealed space. At that point, you would be required to follow the listing and hydraulic requirements of that sprinkler. There are also sections that would need to follow minimums like the 3000ft² requirement if applicable or items out of Chapter 26.
Pete H
2/25/2025 08:28:08 am
Agree with Dan, the ceiling (and sprinkler protection underneath it) count as a separate level, therefore the interstitial space would be able to use the design area reduction assuming it fits all the requirements thereof.
Tommy Hintz
2/25/2025 09:47:56 am
I would calculate the shell (upright) system using the elevations from the roof deck down to the floor. It ensures that the shell system is sized properly for any future ceiling height. There really isnt much difference between a 35.5% reduction compared to 40%, maybe 1 extra sprinkler. This allows the owner to have the best system for future needs.
Casey Milhorn
2/25/2025 10:55:18 am
Agree with the other comments, BUT I would consider using a listed combustible concealed space head from a practical standpoint. Many advantages to using a specific concealed space head, even when not required to. Make sure to read the entire specification sheet and follow all requirements. Different manufacturers have some nuances on how they are designed and installed.
Jack G
2/25/2025 02:36:25 pm
Since the roof deck is combustible, maybe the walls are too, and the ceiling —- one or all of the above, this is not a concealed combustible space where sprinklers can be omitted ( and use the 3000 sq ft rule for the area hydraulic calculation below the ceiling. Leave a Reply. |
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