Shared Risers, Shutoffs and the Neighbor You Flood

Why this matters

When a single-family house goes dry, one household is inconvenienced. When a riser goes dry, ten or twenty households are, and the water damage that follows rarely happens in the unit you were working in. It happens two floors up, where someone turned on a faucet while the water was off, found nothing, walked away with the stopper in, and was out when you restored the riser. Or it happens three floors down, where a forty-year-old valve you never touched started weeping because the pressure surge on restore unseated its packing. The repair can be perfect and the job still ends in an insurance claim. Most of that is preventable with how you shut the riser down, how you drain it, and how you bring it back.

What a riser system looks like

A riser is a vertical pipe carrying water up through a building. Each floor's unit, or the units on one line of the building (a stack), takes a branch off it. Isolation valves usually sit at the bottom of each riser in a basement or mechanical room, sometimes at the top too, with a drain valve at the low point and often an air vent or a test fitting at the top.

   Typical domestic cold riser, one stack

   roof   [air vent / test fitting]
            |
   12  ----+---- branch -> unit 12C (stop under sink)
   11  ----+---- branch -> unit 11C
    :       |        :
    3  ----+---- branch -> unit 3C
    2  ----+---- branch -> unit 2C
            |
   bsmt  [isolation valve]--[drain valve] -> floor drain
            |
        from building main / booster pump

Three things in that drawing cause most of the trouble. The isolation valve is often the original, rarely operated, and may not close fully or reopen at all. The unit stops under sinks and behind toilets are just as old, and the only thing keeping some of them dry is that nobody has moved them in twenty years. And nothing in the drawing tells you which units are actually on this riser; buildings are full of kitchens fed from the bathroom riser of the unit next door. The served list has to come from the building engineer and be written down unit by unit, which is the job of See related: The Multifamily Building Job Intake SOP. The notice period and its content live there too.

Tall buildings also split their water into pressure zones, so static pressure differs a lot from floor to floor; See related: High-Rise Hazards for Residential Trades.

Closing an old valve without breaking it

Most riser isolation valves in older buildings are gate valves: a wedge on a threaded stem that drops across the pipe. They fail in characteristic ways.

• The stem packing weeps when the stem turns, because the packing hardened in place. A slow drip at the bonnet nut while you close is common; a quarter turn of the packing nut usually stops it. A spray is not, and means stop and let the engineer decide.
• The wedge separates from the stem. The handle turns, keeps turning, and nothing closes. This is the failure that floods units, because everything looks right.
• The wedge will not seat because scale is lodged under it, so the valve passes: flow slows but never stops.
• The valve closes and will not reopen, or the stem snaps on reopening, which leaves the riser dead until a valve is replaced under a building-wide shutdown.

So: the engineer operates building valves, not you. Count the turns to close and write the number down; you will reopen by the same count. Close steadily, not with a cheater bar. Never force a valve that has stopped moving; force is how stems snap.

Proving the riser is actually off

A closed handle is not proof. Open a fixture on the lowest floor of the stack and one on the top floor. Flow should taper to nothing within a minute or two as the column drains. A hose-bib pressure gauge on the drain valve gives a cleaner answer: after the riser drains, it should read zero and stay there for five minutes.

Expected drain volume is a second, underused check. Work out how much water the riser and its branches hold before you open the drain. If far more than that comes out, or the drain never stops running, the isolation valve is passing, and you have learned it before cutting a pipe rather than after.

Draining down

Open the drain valve at the bottom and something at the top: the vent, the test fitting, or a top-floor fixture. Without an opening at the top, the column holds by vacuum and dribbles. With one, it drains fast, so route the drain hose to a floor drain you have confirmed is open and can take the flow, or to buckets you can count.

The hot riser holds water at the building's set temperature. Treat drained hot water as scalding: hose tied down at the drain, nobody's hands in the stream, and the floor around the drain kept clear because wet concrete in a mechanical room is slick.

Restoring without water hammer or leaks above

Water hammer is the pressure spike when moving water is stopped or slammed into a closed end, and a refilling riser is a column of water racing up toward closed valves with trapped air ahead of it. Restore slowly and the spike never forms.

• Close the drain valve. Leave the top vent or a top-floor fixture open to let air out.
• Crack the isolation valve a quarter turn and listen. Let the riser fill at that rate until water, not air, reaches the top opening, then close it.
• Open the isolation valve the rest of the way to the counted number of turns, slowly.
• Purge air at fixtures from the top floor down; air left in the branches sputters out of faucets and can slam a toilet fill valve.
• On the hot side, the building's recirculation pump stays off until the riser is purged, so it does not pump air.

Then walk the stack. Every unit on the served list, if you have access arranged: look under each sink and behind each toilet for a drip at stops that were not leaking before, check that no faucet was left open, and look at the ceiling of the unit below the work. Sediment knocked loose by the shutdown clogs aerators and fill valves; occupants will call about low flow the next morning, and a note in the notice that explains it saves the calls.

Avoiding the riser shutdown in the first place

The best riser shutdown is the one you did not need. Two tools shrink how often it happens.

A branch isolation valve. Many older buildings have no shutoff between the riser and each unit, which is why a leaking shower valve in one unit takes water from a whole stack. When the riser is already off for a repair, adding a quarter-turn ball valve on the unit's branch costs a few minutes and means the next repair in that unit needs no riser shutdown at all. Because the branch is often a limited common element, get management's approval for the addition in the same work order; the building may want valves added on every unit while the riser is drained, which is a bigger and better job.

A pipe freeze kit. A freezing kit chills a short section of pipe until an ice plug forms and holds back the water, isolating a branch without draining anything. It works only on pipe sizes the kit is rated for, only with no flow in the pipe (a running recirculation loop will not freeze), and only if nothing downstream is opened that could push the plug out. Wear the gloves and eye protection the kit's instructions call for, because the refrigerant and the frozen pipe both cause frostbite on contact, and keep a hand on the plan for what happens if the plug lets go: a plug that fails sends full pressure out of an open pipe, so the cut is made with the riser valve located, the engineer reachable, and a cap ready. Treat a freeze as a convenience for small branches, not a substitute for a riser shutdown on the riser itself.

Worked example: a 12-story cold riser

A plumber is replacing a section of corroded branch in unit 8C, which needs the C cold riser off. The engineer's list is units 2C to 12C, eleven units. The riser is 1-1/4 in copper, about 120 ft from the basement valve to the top fitting.

Expected volume. A 1-1/4 in copper tube of the common wall thickness holds about 0.065 gallons per foot, so 120 ft is about 7.8 gallons. Each unit has, as an illustrative estimate, about 30 ft of 1/2 in branch at about 0.012 gallons per foot, or 0.36 gallons, and eleven of those add about 4.0 gallons. Total, 7.8 plus 4.0, is about 12 gallons. With the drain open and the top fitting vented, that should be done in a few minutes.

What happened. The engineer closed the valve in 14 turns, the plumber opened the drain and the top fitting, and the drain ran hard for four minutes and then kept running as a steady pencil-thick stream. After ten minutes the bucket count was well past the 12 gallon estimate and still rising. Conclusion: the valve was passing. The plumber did not cut. The engineer worked the valve open two turns and closed it again to flush the scale off the seat, the stream stopped within a minute, and the gauge on the drain read zero for five minutes.

Restore. Drain closed, top fitting open, valve cracked a quarter turn. Water reached the top fitting after about six minutes, the fitting was closed, and the valve was opened slowly to 14 turns. The plumber purged air from 12C down to 2C with the occupants' help, arranged by management.

The walk. Unit 5C's toilet stop was weeping at the packing nut, a slow drip that had not been there that morning. A quarter turn on the packing nut stopped it, and the plumber photographed it before and after and noted it in the job record, because a leak found by you on the walk is a repair note, while the same leak found by the occupant a week later is your flood.

What changes the answer. If the valve had kept passing after a flush, the job would stop and the riser go back on: cutting a pipe that is still fed means water running out of the cut under full pressure. The fix then is a valve replacement or a freeze plug on the riser, scheduled by the building with its own notice, not a workaround in 8C.

How to verify you got it right

Before you leave the building: the drain valve is closed and the gauge or fixture showed zero before you cut; the isolation valve is open to the same number of turns it took to close; every fixture on the served list delivers water without sputter; every stop you saw on the walk is dry; and the job record shows the valve, the turn count, the served list and anything found on the walk. If a unit on the list could not be entered, record that it was not checked, so nobody later assumes it was.

References

• See related: The Multifamily Building Job Intake SOP
• See related: The Unit Below Flooded During Our Repair
• See related: High-Rise Hazards for Residential Trades
• See related: Condo and Multifamily Work: Whose Property Is It?