Sidewalls Allowed in Deep Wood Beam Pockets?

3/21/2023

We have very deep beam glue-laminated timber construction that just has the laminated wood exposed to below.

The beams are very deep; 2'-9" deep. These form bays that are 13'-9" x 13'-9", many with smooth ceilings. The area below is light hazard.

Can sidewall sprinklers be used up in these coffered areas?

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9 Comments

Pete H

3/21/2023 07:04:02 am

Not really conceivably.

Your sidewall is horizontal, letting you go a maximum 12" below the deck. So you still need to spray under a 1'-9" obstruction, or 21" obstruction.

Say you could be centered in the 13'-9" bay. You're 6'-10.5" off the obstruction.

Check Table 8.7.5.1.3 (NFPA 13 2016 Edition).

To spray underneath an obstruction 14" below the deflector, you need to be at least 8'-6" away (which is where the table maxes out). Not only is this still not enough to spray underneath the beams to the side of the sprinkler by being too close to the obstruction, you still go 5" greater than the Table even has allowances for in the depth of the obstruction. And extended coverage or vertical sidewalls just give you worse numbers/allowances.

Unfortunately you need to protect each pocket/bay separately. And given the image, sidewalls are not really optimal for doing that here.

Pete H

3/21/2023 07:09:23 am

...21 minus 14 is 7, not 5. Let's just pretend that's a typo.

Dan Wilder

3/21/2023 07:50:31 am

Can you, sure. Need to confirm the lower perimeter soffits bounding the bays are less that 16",so providing a back to back installation is feasible within every pocket (13-22' 10.3.4.1.4.1 -The maximum width of the lintel or soffit shall not exceed 16 in. (400 mm).)

There is no ceiling pocket omission allowance for sidewalls.

Unless this is also considered "Limited-Combustible", the maximum width (throw) of the pocket is limited to 12' so you're now having to put in 2 sprinklers per bay facing each other. (13-22' Table 10.3.3.2.1) or use extended coverage sidewalls.

Little caveat...you'll be in the maximum spray area of sidewalls within each pocket going against (13-22' 10.3.4.1.6
Sidewall spray sprinklers shall be permitted to be installed on opposing or adjacent walls, provided no sprinkler is located within the maximum protection area of another sprinkler.) so again, an EC option is required.

Double check soffit depths against walls for possible requirements of added pendents beneath (13-22' 11.3.5.1.3.1*
Where soffits used for the installation of sidewall sprinklers are less than or equal to 8 in. (200 mm) in width or projection from the wall, additional sprinklers shall not be required below the soffit.)

This picture seems to indicate either a skylight or other upper soffit lighting above the plane of the upper step in within each pocket....? Throws yet another wrench as to spacing requirements is so.

Jesse

3/21/2023 09:03:35 am

Wow that's a mess. I think Dan's on the right track in finding an allowance to do it. I just don't think its the best means to protect this area. I think I'd be looking at other options.

Paul Pinigis

3/21/2023 09:23:36 am

Yes, you can treat each bay as a room and protect it with a sidewall.

HASSAN ABDALLA

3/23/2023 05:26:29 pm

That is what I was thinking considering pockets like room each.

Dave

3/21/2023 11:00:38 am

I assume beam penetrations (for the sprinkler lines of for back-to-back sidewalls) are out of the question, and I assume the architect is going to want the sprinkler lines running off to the side of the cells. I am also encountering similar configurations in historic buildings (e.g. McMenamins) with plaster coffered cells like this, and see effective use of sidewalls, horizontal or vertical, paying particular attention not to exceed the maximum deflector to back wall distance. I expect to see a lot of new challenges with new forms of engineered lumber, CLT, DLT, mass timber, etc.

Dave

3/21/2023 11:03:06 am

...But are there obstructions including those created by surface-mounted lights?

Glenn Berger

3/21/2023 11:15:47 am

Based on the dimension you provided, each pocket requires sprinkler protection.

You did not mention the hazard of the space provided. If LH, then one sprinkler per pocket required. If OH, then multiple sprinklers appear to be required.

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Sidewalls Allowed in Deep Wood Beam Pockets?

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