Can Close Walls Create Obstructed Construction?

1/22/2024

Can full height walls within a room create an obstructed construction situation in an otherwise unobstructed construction building?

As an example, you have a room with full height walls and a single exposed beam (in noncombustible construction) with the distance from the centerline of the beam to both parallel walls less than 7'-6".

If allowed to define this as obstructed construction, a single sprinkler 1" to 6" below the bottom of the beam may be sufficient. If not, it may require a sprinkler on both sides of the beam.

In a multiple-office type of occupancy this could save a lot of sprinklers. This example is assuming following all the rules for obstructed construction and the depth of the beam being such that you can't use the obstruction to sprinkler discharge rules to avoid the obstruction.

Thanks in advance.

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6 Comments

Dan Wilder

1/22/2024 07:45:14 am

All references to 13-19' Edition...and sorry this is a long read

You would need to further define if your example is for a ceiling with an obstruction parallel to the walls or if it is truly a structural beam (bear with me).

Obstructed & Unobstructed terms reference both ceiling and roof deck construction types. For example, 3.3.41.2(g & h) Annex reference "...suspended ceilings & smooth monolithic ceilings..."

Now, this is where it may split in thought process as I have argued with plan review, inspectors, and other reviewing entities....
Most of the examples in 3.3.41.1 Annex specifically reference structural elements...beams, girders, trusses, bar joists, TJI's, Concrete Tees and all of these are without a maximum pocket size...except for (5) which is for Panel Construction that does not have a maximum spacing requirement between members, just an overall FT² area limitation.

So, is this structural or not (even though, based on cross section alone they would be nearly identical). There is no depth restriction with obstructed construction, just deflector distance and ability to spray beneath adjacent members.

10.2.6.1.2 (SSP/SSU) for deflector spacing all states "structural" for distance below ceiling with the exception of (3) where sprinklers are in every bay 1"-12" down.

Now check out the definition for Ceiling Pocket (Architectural feature, not structural) and that annex section stating that the intent is not to apply this definition to structural or framing members. That allows skipping of pockets, provided 10.2.9 is followed, but does not allow deflectors within pockets to follow obstructed rule distances....oh ya, and they need to be QR and there are remote area implications.

Toss in the requirement if the sprinkler is listed/approved for use in obstructed construction, which isn't an issue when applying ceiling pocket rules.

Also, the maximum spacing allowance for sprinklers in obstructed construction is less than unobstructed by ~60% (130 vs 225) so you're taking a hit even if you can remove sprinkler within some pockets and not typically enough to make it worth while in the long run.

I'm open to both directions soley based on what the physical layout provides, but it does come down to how much I want to debate my position risk vs reward.

If you made it this far, glad you're coffee was hot & full when starting. I'm gonna plug the NFSA EOD publication as well since it helped with this response and is a great reference publication for questions like this. I'm not sponsored but Mr. Meyer did contribute to the book and does receive some royalties (for transparency).

The free searchable index if you would like to review what's in the books:
https://member.nfsa.org/Shop/Product-Catalog/Product-Details?productid={B4F53990-2EC8-EA11-A812-000D3A19F370}

The 3-Volume set link:
https://member.nfsa.org/Shop/Product-Catalog/Product-Details?productid={131E4CBC-2917-EC11-B6E6-000D3A8F652D}

Tech Notes May 2019 #8
Tech Notes May 2020 #12

Chris

1/23/2024 07:16:40 am

Thanks for your response Dan. That's a lot to chew on. Or drink coffee on.

Glenn Berger

1/22/2024 08:15:19 am

Exposed construction near room walls can indeed cause obstructed construction at the perimeter ONLY.

Having a deep beam near a wall will require special placement of sprinklers. This is a very common occurrence.

This does not cause the entire room to be deemed obstructed construction.

Casey Milhorn

1/22/2024 09:38:24 am

Dan covered the proper path to cover this perfectly. I would add that obstructed and unobstructed construction can exist in the same building, same area, and even the same compartment (imo).

From a practical perspective, if we are talking light hazard, I think one sprinkler is the appropriate call (if I understand the details correctly). I think that is the intent of the standard and just good fire protection. More is not always better.

Aesthetically, you might get some pushback having a sprinkler that low in the room.

Anthony

1/22/2024 03:05:08 pm

This hypothetical seems to try to do a lot of work that the small room rule already does. Just saying if you are trying to reduce sprinklers there are better ways than to manufacture obstructed construction.

CHRIS

1/30/2024 08:32:20 am

Help me understand what the small room rule has to do with obstructed versus unobstructed construction?

Can Close Walls Create Obstructed Construction?

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