Limit of Service Main in Basement Before a Riser?

2/21/2025

NFPA 13 is clear about a limit of 10 feet under a building before pipe needs to turn up and into a building (with exceptions for trenching).

What about pipe exposed within a basement?

Is there a limit to how far an underground service can run exposed within the building before the system riser?

Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

9 Comments

Dan Wilder

2/21/2025 08:00:27 am

Couple things come to mind on this...

Pipe Material
The penetration through the basement wall (horizontally) using DI pipe typically transitions to steel within a couple feet. Steel is cheaper and easier to work with, less of an issue with restraint and better hanging requirements. Now, I have seen above ground DI pipe installations over several hundred feet, so I do not think there is any issue there provided the hanging, bracing, and restraint issues are adequately addressed, especially if there is a potable water aspect. C900 plastic is susceptible to UV light issues and more environmental issues along with the hanging, bracing, and restraint requirements.

Underground piping materials can and will leak so that should also be a great reason to not use it over long distances exposed.

Shutoff/Control Valve
Having the ability to shut down an incoming line when it enters the building should be (IMO) as soon as available, but there are no requirements to my knowledge. Typically, the next available shutoff location is either via a street key/valve box or backflow (in or out of a pit) and those locations, in most cases, are controlled by other entities and not readily available for access. This may not be a "riser", but just a control valve.

I had a retrofit/upgrade to a building with the underground line coming in on the B1 level and went down to the B3 level (several hundred feet, but did transition to steel just inside the building) to a fire pump before there was any control valve. The shutoff outside was a city owned street key in the middle of a 5 lane, one-way downtown street which was an absolute nightmare to get the ROW permitting, barricading (because that was the SOP for shutting down a lane to get a crew to close the valve) to get access so we could add a new valve at the B1 penetration and avoid the process.

Glenn Berger

2/21/2025 08:09:57 am

Concur with the Dan's write-up. I also want to add that the 10 foot rule is limit the number of pipe segments and fittings that are located below the building and therefore be inaccessible.

Chad

2/21/2025 08:14:37 am

I would explain to the owner how hazardous it would be to have pipe that they cannot shut off, running through their building more than a few feet. As an AHJ, I might determine that as a hazard and tell them they have to have a shut off/flow switch as it enters…. no one can tolerate a a large main flowing water with no alarm connected to it…. You could fill up a basement pretty quick with no warning.

Christopher Nelson

2/21/2025 09:25:53 am

As a designer and now AHJ, I would accept more than 10 ft if its accessible. Thats the whole point of allowing it if its trenched, accessibility.

Christopher Nelson

2/21/2025 09:27:43 am

Also the point of yard PIVs, yard/street boxes, etc to shut off the section before the riser.

Jack G

2/21/2025 10:40:10 am

Sometimes a specific type of piping material is specified by the water company. Example— Chester water, aqua American water , DI pipe is specified all the way up to the water meter and or the BFP. So depending on how close to the service wall, depends on how much. ( uniflanged for DI pipe )

Jesse Cecil

2/21/2025 11:33:03 am

Some good comments here. I'd add a couple things.

This is pretty common, but once the pipe stubs up it becomes an above-ground fire service main. Its not uncommon for an above-ground fire service main to run several hundred feet.

But there are risks. A year ago or so, had a school where the 6" DI UG stubbed up in a corner of a building, ran up into the attic as a 4" Sch. 10 above ground fire service main, and then 140 feet to the riser room in the opposite corner of the building. The water department had a falty PRV which caused a pressure surge to 190-psi. A check valve just beyond the 6" DI stub in held the pressure on the system and a coupling failed. There was no control valve as this pipe was upstream of the riser. Hence, shutting the sprinkler control valve had no effect. We and the fire department had to find the underground NRS valve to shut it down.

Put a valve on it.

Anthony

2/24/2025 06:53:47 am

ALWAYS put a "city valve" on a stub up.

Ryan Hinson

2/21/2025 11:51:17 am

NFPA 24 (2022) Section 10.1.4 allows the the underground piping to daylight into a building through a slab or wall up to two feet regardless of pipe type. Beyond this, one must use those pipe types allowable for aboveground service per NFPA 13 (2022) Table 7.3.1.1. Though allowable per code, I would NOT recommend extending the UG pipe if PVC or HDPE is used since these pipes are only listed for use in FP for underground. The mfgrs' own listings indicate this.

I recommend transitioning to restrained DI or using a SS IBR prior to extending under the slab or through the wall. Once inside the building (as has been previously stated), I'd transition to CS and run to where the riser is located.

Though some leakage is allowed on UG pipe per NFPA 24 Section 10.10.2.2.6 and NFPA 13 Section 6.10.2.2.6, I would not allow any leakage (visual or otherwise) on this lead-in section in accordance with NFPA 13 Section 29.2.2.1.

While I think it is a good idea to have a flow switch on this piping (upstream of any risers due to the length between, I see no requirement for it since each individual system riser is already required to be hydrostatically tested and have automatic waterflow detection. This pipe section technically meets both the definitions of a 'system riser' being between the water supply and the cross or feed mains per NFPA 13 Section 3.3.225 AND the definition of a 'private fire service main' per Section 3.3.170.

As you did not mention whether this space is sprinklered, it should be noted that NFPA 13 Section A.9.1 does still recommend AGAINST routing piping through unsprinklered spaces unless such spaces specifically allowed per the standard.

Limit of Service Main in Basement Before a Riser?

Leave a Reply.

ALL-ACCESS

SUBSCRIBE

COMMUNITY

YOUR POST

PE EXAM

FILTERS

ARCHIVES

PE PREP SERIES