Duplex Repiping With Tenants In Place: How It's Staged
Quick Answer: A small multi-unit building is repiped unit by unit. New lines are run and pressure-tested while the old system remains live, so each unit loses water only during its own changeover, usually for part of one day rather than the whole project.
At six forty on a Tuesday, the tenant in your front unit is in the shower with shampoo in her hair and a shift starting at eight. The crew's van is already at the curb. The lead needs the building's water down by seven thirty to tie a new line into her bathroom wall.
She is not a detail of your project. She is the constraint it gets designed around. Nearly every real decision on a repipe in an occupied building traces back to her morning: which unit is disturbed today, how many hours her taps run dry, whether she can use her own bathroom at noon, and how much warning she had.
The pipe is failing on its own schedule, and the people living over it are on theirs, and most of what you are buying is the work of fitting one to the other.
Why a Small Building Is Not Just a Larger House
Three things separate duplex repiping from the same job in a house on the same block.
Whether one service line and one meter feed the whole building: Many two- to four-unit buildings from the era when galvanized steel was the standard supply pipe were plumbed the way the single-family houses around them were: one line in from the street, one meter, with branches distributed inside to each unit. Others are separately metered. Which one you have is established during the walkthrough by finding the meters and tracing what each feeds; the answer governs the staging. Work on a branch inside a unit touches that unit. Work on a line two units hang from touches both households at once, so it gets a day of its own. Separately served units have no building-wide cut-over day at all.
Shared walls carry shared pipe: The wall between the front unit's bathroom and the rear unit's kitchen may be the chase feeding both, and the fixture on the far side comes out of that same cavity. The route a crew picks is partly a decision about which tenant absorbs which day.
Same age, same pipe, all of it: Galvanized closes up from the inside, and every branch went in at once. If the front unit's hot side is down to a trickle, the rear unit's is somewhere behind it on the same path. The problem is building-wide, and the disruption still arrives one household at a time.
One boundary: this is written for a building you own outright. Where an association controls the shared walls and common systems, scheduling authority sits elsewhere, and the sequence gets built around that.
How the Work Is Sequenced, Unit by Unit
Phasing works because of one habit of the trade: the new system is built alongside the old one while the old one still carries water. Trunks are run, branches dropped to each fixture group, and the whole thing pressurized and proved before anything is cut. That keeps the outages small. A tenant's water goes off for the changeover, not for the rough-in.
| Stage | Crew's work | Water off for | What that household notices |
|---|---|---|---|
| Walk-through | Routes, fixture groups and valves mapped | Nobody | A short visit in each unit |
| Trunk lines | New mains through attic, crawl or common chases | Nobody | Noise overhead, openings in common areas |
| Unit one rough-in | Branches dropped to every fixture | Nobody | Crew in all day, walls opened, water still on |
| Unit one changeover | New lines proved and tied in, old ones capped | Unit one | Water off for a window in one day |
| Unit two, then any others | The same pattern, next door | That unit | The same day, one unit over |
| Shared items | Common laundry, shared heater, hose bibs | Everyone, briefly | A short building-wide window |
| Service tie-in, where the line is shared | New system joined to the building's supply | Everyone | The longest shared outage |
| Inspection and patching | Open work viewed, then closed | Nobody | Access needed, then dust |
The order is not fixed. A crew may take the worst unit first because that tenant is the one calling you, or the easiest first because the lessons make the next one faster. What is fixed before anyone mobilizes is which unit is which, and on what dates.
The Day the Shared Line Gets Cut Over
Where the building runs on one service line, one day cannot be phased through: the day the new system is connected to the line that feeds the whole property.
If the service line from the meter stays, the tie-in is a single connection, and the shared outage is short. If it is being replaced, the day includes excavation and runs longer, because nothing feeds the building until the new run is in and proved. Either way, every unit on that shared line is dry at once, including the one nobody is working in.
Inside that window, the sequence is predictable: isolate at the meter, make the connection, bring the system up, purge air from the highest fixture down, then walk every unit and run every tap. That last walk is how a missed fixture gets found while the crew is still there.
Expect air and color afterward. New pipe fills with air, so the first minute at a tap spits and coughs, and water can run cloudy where scale in the old piping was disturbed. Both clear once fixtures have run.
If your building runs on a single shared service line, the day it is cut over, water will be shut off to every unit at once, including units nobody is working in. Establish that at the walkthrough and tell all of them.
How Long the Water Is Off in Each Unit
Three different outages get blurred together.
Isolation during rough-in: New pipe goes in beside live pipe, so most of this phase needs no shutdown. Where a crew breaks into an existing line to set a valve, the outage runs minutes and often affects one fixture rather than the unit.
The unit's own changeover: The one that lands on a tenant's day. The new branches are already proved, so the work is disconnecting old and connecting new at each fixture group, then restoring and checking. It takes part of a working day, and the unit next door keeps its water throughout.
The building-wide tie-in: Where the service is shared, the shortest in hours, since it is one connection, and the widest in reach.
What stretches any of them is what the walls were hiding: a main shutoff that will not close after decades untouched, a fixture that will not isolate, routing nobody expected. A crew that operated the shutoffs in advance finds most of that early, which argues for the walk-through being its own visit rather than the first hour of day one.
Ask for a schedule that puts water back in every unit before the crew leaves each day, and ask while the sequence is being built. Most crews plan it that way anyway, and one that does not is far easier to change on paper than at six in the evening.
What Your Tenant Lives Through on Their Day
Set the expectation accurately, and most complaints never happen.
Noise. A hammer drill through studs and plaster, a reciprocating saw, hammering to secure new line. Loud, intermittent, early. The part owners underestimate: shared walls carry it into the unit nobody is working in, so your next-door tenant has a loud day, too.
Access. The crew is in the unit for most of the working day, moving between the bathroom, kitchen, and laundry, with a door in use for tools and a van taking up curb parking. That does not fit a tenant who works nights, worth knowing before the date is set.
Fixtures out of service. During the changeover, that unit's sink, tub, or toilet is unusable for stretches, and a one-bathroom unit has no indoor alternative.
Dust and cleared space. Floor protection and sheeting go down on the first morning. Under-sink cabinets, closet walls, and anything hanging where the crew is cutting get cleared beforehand; it's its own short piece of preparation.
Phasing Across Units Is Not Phasing Across Rooms
In a house, phasing is a relief valve: do the hall bath first and the household showers in the other one. That option does not exist here. The tenant in the front unit cannot brush their teeth in the rear unit's bathroom. Each unit is a complete household with one of everything, so splitting a unit's work across three light days buys that household three disrupted mornings instead of one, and the crew three setups.
Crews compress instead: get into a unit, do all of it, prove it, hand it back finished, move next door. That depends on trunk work being finished before any unit's day starts, because a crew that leaves a unit to go run a main will be back in that unit tomorrow.
Scheduling: What the Crew Needs, and What Belongs to Your Attorney
The plumbing half is simple. A crew wants the unit order fixed before it mobilizes, consecutive days rather than scattered ones, a full working day in whichever unit it is in, and one named person who can decide access without a callback. Ask for the whole thing as a grid: each unit, its work days, and the hours its water is off. A morning lost to a door nobody answers does not come back, and the day it was to finish moves to the end.
Give them the building's facts too: where the meter and main shutoff are, which units share which walls, what the water heater serves, whose unit the attic or crawl access runs through, and any tenant whose hours rule out a standard day.
The other half is not a plumbing question. What notice you owe each tenant and in what form, what your obligations are while a unit is disrupted, whether any rent adjustment or compensation for inconvenience applies, and what counts as habitable during the work are legal questions. They are governed by your lease and by state and local law; they vary by jurisdiction and by the terms you wrote; and they belong to your attorney or a landlord association, not to the person holding the pipe cutter. A contractor can tell you which unit it needs on which day and for how many hours. Take that schedule to counsel and let the notice be built from it.
In a rental, the file is read by people who were never on the job, and two of them want things a homeowner is never asked for. A property manager taking over the building first asks for a dated log of which unit was worked on each day and how many hours its water was off, because that is what a tenant's later account is checked against. An insurer asks what replaced the galvanized and where each unit isolates, so the material record and labeled valve locations carry more weight than the photographs. Ask too who holds the workmanship coverage if the building changes hands, since it travels with the property rather than with you.
Have every unit's shutoffs labeled at the valve before the crew leaves. At midnight, a neighbor's failed supply line gets closed by whoever can find the right valve, and an unlabeled one floods the unit below while somebody guesses.
Three parties each need something from the other two, and the schedule holds only as long as all three arrive.
The crew needs a unit it can work in on the agreed day: cabinets cleared, the wall reachable, the dog elsewhere, the door answered. Everything downstream of that morning sits on it.
Your tenant needs a day that ends the way it was described: water back on before the crew leaves, the bathroom usable, the mess kept where it has to be, and a plain answer the moment something runs longer than described.
Both of them need the plan from you: a sequence fixed before anyone mobilizes, one person to call, and no new work added mid-week without anyone being told. And you need the file at the end, since you are the one still holding this building in five years.
The pipe is the manageable part. What decides how this goes is whether three sets of people who do not otherwise speak spend the length of the job telling each other the truth about the time.
Frequently Asked Questions
Start with the building full unless a turnover is already on the calendar. A vacant unit makes a good place to begin: material can live in it, and the crew can prove the layout where a mistake costs nobody a morning, then carry the lessons next door. Waiting on a vacancy nobody has scheduled, with a failing pipe in the walls, is how this goes wrong.
Two contacts are worse than one, because each assumes the other answered. Whoever it is needs authority to decide access on the spot, and a phone they answer during working hours. Settle the entry method before day one too: a tenant present, someone with a key, or a lockbox; each changes what time the day can start.
Your building department decides, and the answer drives your calendar more than your paperwork. Inspections happen while the new lines are still open to view, so if each unit carries its own permit, unit one can sit with open walls waiting for a visit while unit two is roughed in. Ask before you fix the unit order.
Where one line serves the building, it is the component every household depends on; it is buried, and it is reached with different equipment on different kinds of days. If it is original and the same age as the branches inside, doing it in the same mobilization means one building-wide outage instead of a second shared shutdown later.
Common items sit on the shared side, so they fall inside nobody's unit day and are the ones discovered mid-week and pushed to the end. A heater serving more than one unit makes the hot side of the changeover building-wide. Laundry valves in a common room and exterior hose bibs each need their own slot.
From the plumbing side, it is a resequencing problem with a cost in time. That unit's branches can be left roughed in and unconnected while the crew moves next door, but the changeover and the inspection stall behind it, and coming back is a fresh mobilization. Whether you have a right of entry, what notice makes it valid, and what follows a refusal are questions for your attorney or a landlord association.
Get the unit-by-unit sequence and the water-off windows in writing before anyone mobilizes — a licensed plumber will walk every unit, operate the shutoffs, and name the days. Ser Plumbing serves Paramount, Bellflower, and Lakewood. Call (310) 953-3566.
