Calling a plumber in a sprinklered DC rowhouse: which ordinary jobs touch the sprinkler system

Most of the sprinkler systems going into DC rowhouses today are multipurpose: the sprinkler heads hang off the same cold water piping that feeds the sinks. That is cheaper and it is a good design, but it has a side effect nobody mentions at closing. Routine plumbing jobs now touch a fire protection system, and the plumber doing them will not know that unless you say so. This article lists the jobs that matter, the ones that do not, and the two questions to ask before any plumber opens the main.

First, which system you have

Go to where the water service enters the basement. If there is one main shutoff and the sprinkler piping leaves the domestic line at a tee somewhere past it, with no separate sprinkler valve, gauge, or backflow preventer of its own, you have a multipurpose system. If there is a separate riser with its own control valve, a pressure gauge, a drain, and often a backflow preventer, you have a standalone system. The multipurpose versus standalone article explains the difference in more detail. Almost everything below is about the multipurpose case, because on a standalone system the plumber’s work stays on its own side of the riser.

Jobs that touch the sprinkler system

Replacing the main shutoff or the meter setting

Safe, with one caution. While the main is closed, the sprinklers are off, so a job that runs into a second day leaves the house unprotected overnight. The bigger risk is the new valve arrangement. 13D allows a single shutoff for house and sprinklers together, which is what a multipurpose system relies on. A plumber who adds a second valve that isolates the sprinkler loop, so that someone can turn it off without turning off the sinks, has created a valve that the design never assumed and that the standard expects to be either absent or locked open. Ask them not to.

Adding a pressure reducing valve

Parts of the District have high street pressure, and a plumber fixing banging pipes or a failed water heater relief valve will reach for a pressure reducing valve on the main. On a multipurpose system that valve now sits ahead of the sprinklers. The hydraulic calculation that got the permit assumed the street pressure, not the reduced one, and a valve set low enough to quiet the pipes can set it below what the top floor head needs. The valve has to be listed for the service, its set point has to be checked against the calculation, and if the numbers do not close the calculation is rerun. The water service sizing article explains how thin the margin often is on a three story rowhouse.

Water softeners, whole house filters, and treatment units

Every one of these takes pressure, and a filter that clogs takes more over time. The standard allows treatment devices in the sprinkler supply only where they are listed for it and their loss is carried in the calculation. The practical answer is to install them on the domestic branch after the sprinkler tee, so the sprinklers drink untreated water and the sinks get the treated kind. That is how we draw it on every new system, and it is worth asking your plumber where the tee is before the unit goes in.

Repiping, and adding fixtures

A basement bathroom or a basement unit adds domestic demand to the same service the sprinklers use, and the calculation carried an allowance for that demand at the time of design. A modest addition usually fits. A second kitchen and two bathrooms may not, and the sprinkler side has to be checked. Repiping the house in PEX raises a different question: the sprinkler loop is built from pipe and fittings listed for multipurpose sprinkler use, and a plumber who cuts into that loop with ordinary PEX and crimp fittings has replaced listed pipe with unlisted pipe. Domestic branches, fine. The loop itself, no.

Lead service line replacement

DC Water is replacing lead services across the city, and the private side comes free with a right of entry. The new pipe must be at least the size the sprinkler calculation used, and a like for like replacement of a three quarter inch lead service may not be. Tell the crew, or the contractor they send, what size the sprinkler design needs before the trench opens. The water service article has the sizes that come up.

Backflow preventers

A standalone system in the District usually has one, and it is tested on a schedule. A plumber who swaps or rebuilds it is doing sprinkler work, and the test result goes on file. The backflow article covers who tests it and what the test involves.

Jobs that do not touch it

A water heater swap on a multipurpose system is on the hot side and leaves the sprinklers alone, unless the plumber repipes the cold tee to reach it. Fixture replacements, drain and sewer work, a new hose bib, a dishwasher line: none of these involve the loop. Winter shutoffs for a vacant house do, and the freeze protection article explains why draining the house drains the sprinklers with it.

The permit side

A plumbing permit covers plumbing. In our experience DC DOB treats changes to sprinkler piping, valves, and supply as fire protection work under its own permit type, with its own inspection, and a plumber cutting into the loop under a plumbing permit has done unpermitted sprinkler work whether they meant to or not. It surfaces at sale, when the buyer’s inspector finds a fitting that does not match the approved drawings, and the buying article explains what that costs the seller. The permit steps article covers how the sprinkler side is filed. The fix is coordination, not a second contractor on every job: the plumber does the plumbing, we do the tee.

Two questions to ask before any plumber opens the main

1. Where is the sprinkler tee, and does your work go ahead of it or after it? Ahead of it means the sprinkler contractor should know first.
2. Will the water be off overnight? If yes, tell the household and the insurer, and get it back on before the crew leaves if the job can be staged that way.

After the work

Turn the main back on slowly, walk every floor and look at every head for a drip, and check the pressure at a basement hose bib against the number on the approved calculation if you have it. If the plumber touched anything ahead of the tee, have the system flowed through the inspector’s test connection at the next annual visit, which the inspection intervals article describes. Small changes on the supply side are exactly what that visit exists to catch. We price a tee relocation or a recheck of the calculation after seeing the basement, since it depends on what the plumber left behind rather than on the size of the house.