Sloped 13D Require 1,950 sqft or 2-Sprinkler Calc?

7/30/2024

For a single-family home with a 6 in 12 sloped ceiling (roof) that is a combustible wood structure.

Does this need a 1,950 sqft calculation due to the slope, or just two sprinklers as NFPA 13D requires?

Thanks in advance.

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6 Comments

Pete H

7/30/2024 06:47:39 am

Has the architect already called this out as a 13D job in the code sheet?

If so, from NFPA 13D (2016 edition):
10.2.1 For each of the following situations, the number of sprinklers in the design area shall be all of the sprinklers within a compartment, up to a maximum of two sprinklers, that require the greatest demand:
(1) A flat, smooth, horizontal ceiling with no beams up to a maximum of 24 feet above the floor [you don't have this]
(2) A flat, horizontal, beamed ceiling with a maximum ceiling height of 24 ft. with beams up to 14 in. deep with pendent sprinklers under the beam. The compartment containing the beamed ceiling shall be a maximum of 600 square feet in area. The highest sprinkler in the compartment shall be above all openings from the compartment into any communicating spaces. [You don't have this].
(3) A smooth, flat, sloped ceiling with no beams up to a maximum slope of 8 in 12. The highest portion of the ceiling shall not be more than 24 feet above the floor. The highest sprinkler in the sloped portion of the ceiling shall be above all openings from the compartment containing the sloped ceiling into any communicating spaces. [YOU MIGHT HAVE THIS]
(4) A sloped ceiling with beams up to 14 in. deep with pendent sprinklers under the beams. The compartment containing the sloped beamed ceiling shall be a maximum of 600 sq. ft. in area. Th slope of the ceiling shall be between 2 in 12 and 8 in 12. The highest portion of the ceiling shall not be more than 24 ft. above the floor. The highest sprinkler in the sloped portion of the ceiling shall be above all openings from the compartment into any communicating spaces. [You also might have this]
(5) A sloped ceiling with beams of any depth with sidewall or pendent sprinklers in each pocket formed by the beams. The compartment containing the sloped, beamed ceiling shall be a maximum of 600 sq. ft. in area. The slope of the ceiling shall be between 2 in 12 and 8 in 12. The highest portion of the ceiling shall not be more than 24 ft. above the floor. [You also might have this].

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And just make sure to also note:

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10.2.3 For situations not meeting one of the conditions in 10.2.1, residential sprinklers listed for use in specific ceiling configurations shall be permitted to be used in accordance with their listing.

10.2.4 For situations not meeting one of the conditions in 10.2.1 and 10.2.3, the number of sprinklers in the design area shall be determined in consultation with the authority having jurisdiction as appropriate for the conditions.

Ivan Humberson

7/30/2024 08:20:13 am

Also, bear in mind that the language in NFPA 13D states that the design has to be the two sprinklers that require the greatest demand, NOT the two most remote sprinklers. Typically, with a sloped ceiling compartment, the greatest demand from two sprinklers in the compartment will be the highest, most remote sprinkler, and the lowest sprinkler nearest the water supply.

Casey Milhorn

7/30/2024 08:54:03 am

Pete H nailed it. Just make sure you aren't referring to NFPA 13 unless specifically directed by 13D. They are 2 completely different standards and 13D does a fairly good job of pointing you to 13 for certain situations.

Jesse

7/30/2024 10:35:44 am

What Pete said...

I'm also curious as to what code the architect referenced. Did the arc h intend this as a full 13 design?

danefre

7/30/2024 11:19:50 am

Calculation will be per NFPA 13D. If you do not meet the criteria for height (24ft peak) then you need AHJ approval for a more conservative design. We've had success calculating 4 heads instead of 2 for sloped ceilings that exceed 24ft in height. A-frame, log cabins etc. are all designed that way.

One thing I didn't see anyone mention is that the layout will heavily depend on the residential design guide of each manufacturer. They are NOT equivalent and have different maximum slopes. Consult the design guide for whichever manufacturer of residential sprinklers you choose.

Jack G

7/30/2024 12:09:41 pm

If under IBC code, there are at least a dozen conditions where 13d cannot be used, height increases, area increases egress increases , types of construction and more.
If IRC 13 d is allowed with less exceptions.
I agree with all of the above, but I would include 1 more sprinkler in the calculation, call that out, and I m sure the AHJ would not have a problem.
Review Meyer fire 13,13r, 13d and frequently discussed in 2020, 2022 similar situations.

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Sloped 13D Require 1,950 sqft or 2-Sprinkler Calc?

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