Spacing Under 6-ft OK if Sprinkler Under Soffit?

5/8/2020

Looking for an answer to a basic discussion point concerning sprinkler spacing. A pendent sprinkler is on a 10'-0" ceiling which is 4'-0" away (horizontally) from a sprinkler in a lower wide soffit, at 8'-0".

Based on the higher sprinkler being so close to the edge of the soffit, the soffit creates an obstruction for the higher sprinkler. However, the lower sprinkler should it activate will undoubtedly throw water to the floor space directly below the higher sprinkler, yet neither sprinkler will directly spray the other.

Are these two sprinklers (one at a higher elevation and one at a lower elevation) required to be a minimum of 6-ft apart horizontally?

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7 Comments

Mike L

5/8/2020 09:53:23 am

Refer to section 8.6.5.1 (b) or (c) (2016 edition)...or use the handy calculator provided on this website.

Need to know the width of the soffit to be sure, but it seems that a sprinkler head under the soffit is needed as the upper head is to close to the soffit to be able to spray under it.

Jesse

5/8/2020 10:07:09 am

What's the width of the lower soffit?

The Guy With the Question

5/8/2020 10:08:32 am

Width of the lower soffit is 5-ft. More like a lower ceiling area than technically a short soffit.

Keith Heckler

5/8/2020 10:10:18 am

The answer is no, it is acceptable. Te rational for the 6 foot spacing with standard spray sprinklers is the cold solder effect. If closer than 6 feet, then spray from a sprinkler will discharge onto the adjacent sprinkler, thus keeping the response element cool. Since the soffit creates a discharge spray obstruction, the sprinkler under the soffit cannot be dampened by the higher positioned sprinkler.

Franck

5/8/2020 11:12:01 am

Keith is right
It would be the same for 2 sprinkler on both side of a beam.
If the beam creates an obstruction and then requires to have sprinklers on both side, they can be less than 6 ft apart as one sprinkler water pattern cannot wet the fusible element of the other one.
Just be aware that if you have too many situations like this in a given area, it might have some effect on your hydraulic calculation

Anon

5/8/2020 11:56:07 am

I was asked this recently, and I agree with Keith and Franck. Although one sprinkler may spray under the other, there is no direct wetting, so it is acceptable. Full disclosure - I wasn't 100% sure until I read an NFSA informal interpretation that was consistent with this.

Ivonn

5/8/2020 09:38:13 pm

What figure you use to check if it is an obstruction?
the figure Figure 8.6.5.1.2(b) from NFPA 13 Ed.2016 or the 8.6.5.1.2(a)
I think maybe you can apply the (b) for the description

I agree with Keith,Franck and ANON, If the sprinkler is really obstructed you don't need have the minimum between sprinklers, that its to avoid the cold solder effect, sometimes in structures with solid members and sprinklers more delicated like ESFR you can use it, try to obstruct the sprinkler to respect the minimum and maximum between sprinklers and others structural members.

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