Detail Pick-Apart: Wet Shotgun Riser

1/3/2024

We tried out something new a couple months ago with a Detail Pick-Apart covering a dry sidewall sprinkler at a deck. We had a great response - healthy discussion from a wide variety of perspectives.

Way back when we even talked about different parts and purposes for components of a wet riser.

It's the dialogue that I often find the most helpful in seeing and understanding perspective that I simply just don't have.

No detail is perfect, nor is it applicable in all situations. No way. It's one possible solution to some situations.

That said, it can be really helpful to have open discord and learn from it.

Quick rehash on ideas for critique and discord:

USE CASES: What are good use cases for this?
PROS: What benefits does an approach like this bring?
CONS: What are the negatives with an approach like this?
IMPROVE: What ways can this approach be improved?

What critique would you offer here?

Thanks, as always, for being part of making the industry better.

Aaron

1/3/2024 10:39:51 am

Spare head box
Calc plate
4 way brace 2'-0" Max from top
Bell
Note elbow req. on drain discharge.

Steven

1/3/2024 01:15:51 pm

Just the nuts and bolts of it, very nice. I assume the premise of this is to have a universal detail that can be tailored to any shotgun riser assembly.

Add "inside' prior to hose allowance.
Add "Water" to gauge note.
Simple bell note - Notification device per NFPA 13.
Increase flow switch distance to 2ft per data sheets.
Call out point of service location.
Simple BFP note: AHJ approved backflow, supervised as required.
Sleeve as required note at the floor penetration.
Combine the two restraint / in-building riser notes.

Always good to revisit these items with out peers as requirements change.

Casey Milhorn

1/3/2024 10:51:41 am

From a practical perspective, It's rare to have a lead-in match the riser size. Typically the riser is smaller (and can provide a lot of cost savings by being smaller), so a reducer below the backflow would be indicative of a more common riser install. BUT then you go down the road of what will the water department allow before the backflow? Does it need to be cement lined? Can it be a painted grooved reducer? Galvanized? The galvanized pipe below the backflow is a no-no with many water departments.

On the backflow itself, a catchall note to provide minimum clearances per local water department requirements. This can cause a lot of issues if the designer is asleep at the wheel.

A preassembled riser manifold would be more common nowadays, but which one would you show? Probably best to keep it generic.

A note about the audible alarm and where it is to be installed.

Mention the tamper switches for the backflow. (where required).

As mentioned, no perfect detail for every situation. They are almost all different in some way. Great conversation starter.

C. Crawdad

1/3/2024 11:45:12 am

Following up on others especially Casey’s excellent comments, I do declare. A few thoughts off the top of my head. I wish I could edit this as I think of more. Interested in further discussion:

• While not required, our specs we require a normally-closed butterfly valve with tamper prior to the hose valves for testing the backflow. That makes me have to make sure what was installed is actually wired for N.C. And the fitter didn’t reverse them.
• Our state goes by the USC Foundation for Cross-Connection Control and Hydraulic Research listings, including for valve type and installation orientation.
• I reject painted or galvanized fittings prior to a backflow, although now some (but NOT all; check literature) galvanized grooved fittings are certified per NSF/ANSI 61.
• Make sure what you are counting on as a flexible coupling at the bottom meets the definition of flexible. Don’t assume a grooved flange is flexible.
• Valves shall be “accessible”
• Provide annular space around floor penetration, try to make sure the GC does not pour this solid. And when picking a location check the structural foundation plan for footings, pads, or grade-beams (location and depth).
• Some contractors like to fabricate the inspector’s test loop rather than use a combination test and drain valve. One AHJ around me still wants a remote wet system inspector’s test.
• Most try not to fabricate the gauge so close to a drain, in order to reduce gauge flutter during test. Then the issue of placing the flow switch far enough from drains and fittings per manufacturer’s literature, of course the argument that it tests fine, and the pre-fabbed riser manifolds have them scrunched close together… (but are listed that way)
• If there is an FDC connection – makes sure it is connected to the correct spot, and includes all the provision required for that FDC, which is a whole other topic.
• How about a check valve at the bottom? I see some designers do this as a rule, while I believe only some situations warrant it?
• One sometimes has to get creative in fitting in a tight space and providing adequate space around the backflow. You might have to think outside of the box with an N-shaped backflow, or even a horizontally-oriented shotgun.
• Coordinate, coordinate, coordinate! Mechanical and electrical love to encroach into and above the “riser room.”

Chris Miller

1/3/2024 11:47:21 am

Domestic water takeoff for combined service was going to be my suggestion as well. Reduced Pressure drain from backflow is a big deal and make this substantially more complicated. Water providers are demanding RP because more is better. The forward flow valves in our area are piped to the exterior (similar to an FDC) instead of hoses through a door. Show the FDC connection. Ours is typically ahead of the water flow switch.

Dan Wilder

1/3/2024 01:34:26 pm

Ever so minor, but the T&D looks to be in backwards and "most" of the T&D MFG's only make it in a right-hand angle configuration.

The pressurized side is on the "bullhead" of the valve with the discharge on the run (drain) side. In a normal closed position, the handle is pointing down.

As I see it drawn, the PRV would never operate and it's sitting in a test condition based on the handle orientation.

Anthony

1/3/2024 02:11:21 pm

Weatherproof piping (galv/painting) and escutcheon on the drain to exterior.

Eric R

1/5/2024 09:26:05 am

Late to the party on this one.

Since the idea behind the post is what an engineering detail would look like, and not a more generic discussion on how wet risers "can" be built, then I would recommend showing the flow-switch, gauge, main-drain as a commercial riser assembly. Like others have posted, they are pretty universally used nowadays anyways, and they provide a way for the engineer to follow up with a specific model that helps eliminate tons of other small details that would otherwise need to be shown like the flow switch separation distance, the now required relief valve that is missing, and the orifice size of the insp-test valve.

The other big one for me is that the FF-test hose valves should be before the flow-switch to help protect the switch from damage. Also I'm pretty certain that you would not include any hose allowance flow when sizing the test header. (barring edge cases like buildings with NFPA-13 inside hose stations maybe?)

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Detail Pick-Apart: Wet Shotgun Riser

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