Sprinkler in skylight ceiling pocket

[carlosgw]

A skylight in an otherwise unobstructed ceiling - should the sprinkler under the skylight be with-in 12" (1" - 12") of the skylight or do obstructed rules apply?

 

[cdafd]

What edition of nfpa 13 are you using

 

[fpst]

Skylights are not mentioned under the definition and examples of obstructed construction in NFPA 13.

Therefore we go with the unobstructed construction rules.

A skylight is considered a type of ceiling pocket in 13 (see the Skylights. section in the Installation Requirements chapter).

Before protecting in the pocket/skylight make sure it's even required. Is the depth of the pocket/skylight not exceeding 36 inches, 1000 cubic feet, the floor below completely protected by other sprinklers, separated from other skylights or pockets by 10 ft, quick response sprinklers used throughout the compartment? If none of that works, you can still omit sprinklers using the specific skylight rule if its area isn't more than 32 sq. ft.

Assuming you still need to protect in the skylight, unless the listing of the sprinkler permits otherwise, or you have fire modeling analysis done to permit lower deflector distances, you need to place the sprinkler 1-12" below the skylight.

However, under the unobstructed construction section, there is a rule that allows vertical changes in ceiling height up to 36 inches to be protected by a sprinkler at a different elevation. So you could have a sprinkler in a skylight under the "eave" of the slope 1-12" down from the ceiling part which is directly above the sprinkler, and it would still be considered protecting the highest point of the skylight as long as the highest point wasn't more than 36" above the sprinkler.

 

[TravisMack]

Remember though, even if it is not needed, you may want to put a sprinkler in the pocket so that you can use the QR reduction. Unprotected ceiling pockets negate you being able to use the QR reduction.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[fpst]

Also remember that what Travis added is only true for unprotected ceiling pockets exceeding 32 sq. ft.

 

[TravisMack]

Correct. I guess I was assuming if he was questioning the pocket, then it would be over 32 sq ft. But, you are correct in that.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[carlosgw]

Thanks.
NFPA 13 2007
The skylight is 35SF.
If the depth is less than 36", can I omit the sprinkler?

 

[cdafd]

are you able to use 2010 edition??




from 2007:::


8.5.7 Skylights. Sprinklers shall be permitted to be omitted from skylights and similar ceiling pockets not exceeding 32 ft2 (3 m2) in area, regardless of hazard classification, that are separated by at least 10 ft (3 m) horizontally from any other skylight or unprotected ceiling pocket. Skylights not exceeding 32 ft2 (3 m2) shall be permitted to have a plastic cover.




from 2010 and 2013:::




8.5.7 Skylights.

8.5.7.1 Sprinklers shall be permitted to be omitted from skylights not exceeding 32 ft2 (3 m2) in area, regardless of hazard classification, that are separated by at least 10 ft (3 m) horizontally from any other unprotected skylight or unprotected ceiling pocket.


8.5.7.2 Skylights not exceeding 32 ft2 (3 m2) shall be permitted to have a plastic cover.

In past editions, the standard was silent on the omission of sprinklers from skylights and similar pockets; however, previous formal interpretations indicated that sprinkler protection was not required for 4 ft × 8 ft (1.2 m × 2.4 m) skylights without establishing a permitted or acceptable depth of the skylight. The concern has always been that, unless a sprinkler was placed in deep skylights or similar pockets, heat would collect in the skylights and delay the operation of sprinklers.
FAQ Do all skylights require sprinklers to be installed within the skylight?
Paragraph 8.5.7.1 permits the omission of sprinklers from skylights that do not exceed 32 ft2 (3 m2) in area and are separated from any adjacent unprotected ceiling pocket or skylight. A single small skylight should not have a significant impact on performance, and the requirement for a 10 ft (3 m) separation between unprotected ceiling pockets and skylights ensures that there will be a sprinkler in between skylights. This sprinkler prevents heat from collecting in multiple adjacent skylights or pockets where sprinkler activation could be delayed (see Exhibit 8.14). The elimination of the sprinkler from under skylights includes skylights that have a plastic cover, as the amount of plastic within these small skylights is not considered sufficient to require a sprinkler.

 

[fpst]

If you are forced to go with NFPA 13 2007, there is a "trick" you can use since 2013 allows it to be unprotected under certain conditions (less than 36", less than 1000 cubic ft, etc). So for the 2007 edition, since it doesn't mention that excemption, you can read between the lines and place the sprinkler on the ceiling next to the skylight as normal, so long as it's covering under the skylight, and as long as the top of the skylight is no more than 36" above the sprinkler on the lower ceiling, the "vertical ceiling change rule" considers it a flat ceiling - therefore not a pocket...

I wouldn't go with that except to convince the AHJ it's correct per NFPA 2007, knowing that you are not cheating because the 2010/2013 edition would allow the same thing for a slightly different rule.

 

[carlosgw]

Sorry but I just received new info from the architect:
The skylight is 42"X42" and roughly 36" deep. Then the pocket widens out to 6'-10" X 6'-10". This part is 2'-7" deep.

So if I put a sprinkler up in the skylight and treat the rest of the pocket like a pocket?
The sprinkler would just be covering the skylight. We do not want other sprinklers in the pocket.