Are Flexible Couplings Req'd For Tall Riser?

9/19/2023

Are flexible couplings required at riser for vertical support?

My project has a vertical support for a 30-ft long 6-inch riser.

I used a riser clamp with two wall-mounted welded brackets to provide vertical load hanger at about 20-ft AFF.

The inspector commented that I have to provide a flexible coupling above and below within 24" of the point of attachment. His reasoning is: 18.2.3.1(6) NFPA 13 2022 edition (6) Within 24 in. above and 24 in below any intermediate points of support for a riser or other vertical pipe.

Anyone has suggestion for better way to put a vertical support at the riser?

Is one ATR hanger at the top of the riser sufficient?

Thanks in advance.

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10 Comments

Jim Phifer

9/19/2023 08:22:41 am

You didn't state if this project was located within an earthquake zone.
Chapter 18 only applies where seismic protection is required. If it is a requirement, then yes, the flexible couplings are required.

Jesse

9/19/2023 08:31:23 am

Is your project in a seismic zone.

Todd

9/19/2023 08:45:34 am

What is the building's Seismic Design Catagory?

That will determine if seismic restraint is required or not.

Buildings can be within 'seismic zones' and not require seismic restraint.

Brad K

9/19/2023 09:02:09 am

Addressing the top of riser bracing. If Seismic is required, 13-18.5.8 (2019) shall be provided with a four-way brace.
If Not Seismic, I recommend considering a four-way brace if there are no other means of horizontal support like a landing within 7 to 10 ft. I don't think the ATR would be adequate.

Inspector

9/19/2023 09:12:00 am

I have to say as an inspector, I think this is a good catch. I understand that it may be inconvenient, but having that much vertical pipe above and below that support could cause a lot of pressure at the support if the building/sprinkler system were to shift back and forth. Even if the sprinkler system is braced throughout, the wall where your support is on the riser could move independently of the sprinkler pipe and cause an issue. Limiting the movement of the pipe could cause it to break disabling the entire system.

Even assuming there was no fire to accompany the seismic event, the massive flooding that would occur from a 6 inch riser pouring into the building would be a disaster.

Dan Wilder

9/19/2023 09:43:43 am

The first question is a little confusing (couplings don't provide support), so I am reading it as "Are flexible couplings required on a riser at the point of vertical support". This is also assuming this is a seismic application but since soo many AHJ's apply riser requirements to non-seismic areas, any reference from Chapter 18 technically should not apply.

As for vertical support, I've seen horizontal offsets to catch hangers or a riser clamp (via a knee bracket like an Eaton B3067 or similar based on structural approvals)

Looking at Chapter 17 first, based on that total distance of a riser, you'll need 2 points of support - Top & Intermediate:

17.4.5.1 - Risers to be supported by clamps or hangers on the horizontal connection within 24" of the C.L. of the riser.

17.4.5.5 for distance between supports not exceeding 25' (technically in multistory buildings but tall buildings tend to get lumped into this requirement), an intermediate support is required based on a total riser length of 30'.

Then Chapter 18 for where flex couplings are required (again, based on seismic requirements):

18.2.3.1 (1) Flex coupling required within 24" of the top and bottom of all risers.
18.2.3(6) then requires a flexible coupling within 24" above & below the intermediate support for a riser.

The only technical work around would be to have a horizontal offset somewhere below the 25' mark, provide the flex couplings and hanger as required for the initial vertical run, provide the 4-way brace and hanger (top of riser), then continue vertical for the last bit but as the pipe is still considered a "riser", you'll need to provide one additional flex coupling (riser is greater than 3' but less than 7') and an additional 4-way brace (18.5.8.1 as the last piece exceeds 36") so in the end, it's not saving anything if in a seismic area.

DAVE

9/19/2023 01:10:14 pm

^^ This.
Distance between supports for risers shall not exceed 25 ft.
9.2.5.5 (2016); 17.4.5.5 (2019)

Flexible couplings shall be installed…. Within 24 in. above and 24 in. below any intermediate points of support for a riser or other vertical pipe
9.3.2.3.1(6) (2016); 18.2.3.1(6) (2019)
This is under “Multistory Buildings” however I would think the upward thrust / axial expansion mentioned in the handbook commentary applies for any similar situation.

James Art, FPE

9/20/2023 10:42:50 am

SOME FLEXIBILITY:
NFPA 13 recommends the sprinkler system move with the building in most places, and perhaps unintentionally encourages rigid mechanical couplings (to eliminate some braces).

I live in EQ country (and note that other areas not so classified,like near the Mississippi, may possibly have seismic events).
I inspected over 50 high rises after the Loma Prieta,
and I have a different suggestion:

A little movement may be good, better than breaking.
I encourage the USE OF FLEXIBLE Grooved Mechanical Couplings, especially at corners, where main pipes change directions.

Jim

Luis

11/21/2023 02:47:20 pm

So if I have a riser in a vertical pipe chase, without floor penetration or offsets, and I support it via brackets anchored to a wall, for example, every 10ft, I would need to place 2 flexible couplings near each bracket?

Luis

11/21/2023 02:48:44 pm

(Assuming it is on a high seismic area)

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Are Flexible Couplings Req'd For Tall Riser?

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