“So do I fix it, or do the whole house?”

Nobody calls you for a repipe. They call you for the third pinhole leak this year, and somewhere in the middle of that conversation the real question comes out. How you answer it is the difference between a $340 repair and a job that keeps two people busy for four days.

It is also the easiest job in residential plumbing to lose money on, because the plumbing is the predictable part. What kills repipes is everything around the pipe.

1. When it is honestly a repipe

You are not trying to talk anyone into anything. There are a handful of situations where continuing to patch is the worse advice, and if none of them apply, say so and do the repair.

• Multiple failures in the same material, in different placesOne leak is an event. Three leaks in eighteen months on the same copper is the material telling you the whole system has the same remaining life. Ask them to count — most homeowners undercount until you make them list them.
• Known problem materialPolybutylene, and galvanized steel that has been in the ground or the wall long enough to close up. Galvanized narrows from the inside, so the symptom is falling pressure at the far fixtures before it is a leak.
• Water chemistry that is eating the pipeAggressive or very soft water, high velocity at fittings, or stray current. If the cause is still there, the repair fails again in the same way. Get a water report before you promise a material will last.
• Pressure that never made sensePoor flow at multiple fixtures at once, especially upstairs, on a system where static pressure at the hose bib reads fine. That is a sizing or restriction problem the repipe actually solves.
• The walls are already openA bathroom remodel, a flood remediation, an insurance tear-out. The single largest cost in a repipe is access. If someone else already paid for it, this is the cheapest a repipe will ever be for that homeowner.

2. Sizing: fixture units in, velocity out

A repipe is a chance to fix the sizing the original builder got wrong, and the two numbers that decide it are load and velocity.

Load comes from water supply fixture units (WSFU). Both major codes assign fixture-unit values per fixture and convert the total to a probable simultaneous demand in gallons per minute — IPC handles this in its water-sizing appendix, UPC in its water-distribution tables. Add the fixture units, convert to gpm, then size the pipe so it carries that gpm with acceptable pressure loss over the developed length, including elevation.

Velocity is the constraint that stops you from just running everything small. Common design practice keeps copper around 8 ft/s on cold and lower on hot — often 5 ft/s or less — because hot water at high velocity is what erodes copper at the inside of fittings and produces pinholes on the elbow after the pump. PEX tolerates higher velocity mechanically, but noise becomes the practical limit long before the pipe cares.

Two other pressure items are worth confirming on any repipe, because they are cheap now and expensive later:

• Static pressure over 80 psi requires a pressure-reducing valve in both major codes (IPC 604.8 / UPC 608.2). Gauge the hose bib before you design anything. High incoming pressure is a common hidden cause of the leaks that brought you out.
• A PRV or check valve closes the system, which means thermal expansion control is now required at the water heater. If you install the PRV during the repipe, you own that too — put the expansion tank on the estimate.

3. Material: pick it for the house, then defend it

Both are code-recognized potable materials in the major model codes. Local amendments occasionally restrict material by location — underground, under slab, or in return-air plenums are the usual ones. Check before you commit on the estimate.

Whichever you choose, run a home-run manifold or trunk-and-branch on purpose rather than by accident. A manifold gives you individual fixture shutoffs and a clean label — it is genuinely better for the homeowner and it is visible proof of quality in a job where almost everything you did is behind drywall.

4. The exclusions that decide whether you make money

Here is the part that turns a good repipe price into a bad week. Write these into the scope before you sign anything, in the customer’s language, and go through them out loud.

• Drywall repair, texture and paintDecide explicitly: do you patch to bare drywall, to texture, to paint, or not at all? “Patch” means four different prices and the customer is assuming the most expensive one. Matching existing texture and an aged paint color is specialist work — price it or exclude it.
• Tile, stone and cabinetryAnything you open in a tiled shower wall or behind cabinets is not coming back the way it was. Exclude the finish restoration and say why.
• Asbestos and lead paintPre-1980 construction. If testing turns something up, work stops and abatement is somebody else’s licensed scope. Put the stop-work clause in the contract, not in the conversation you have after.
• Drain, waste and ventA water repipe is not a DWV repipe. If the cast iron is also failing, that is a separate scope and a separate number.
• Fixture and appliance replacementOld angle stops and supply lines will fail when you turn the water back on. Either include replacing every stop as a line item or exclude them and warn in writing — there is no third option that ends well.
• Water treatment and pressure equipmentSofteners, filters, PRVs and expansion tanks are separate line items, not “while you’re in there.”
• Permits, inspection and re-inspectionState who pulls the permit and who pays for it. If a failed inspection is caused by something outside your scope, say who carries that.
• Slab and concrete workIf the existing run is under slab and the repipe goes overhead instead, say so explicitly — abandoning in place is a decision, and the customer should read it before it happens.

5. Sequencing an occupied house

The homeowner’s real question is not what it costs, it is how long they are without water. Answer it before they ask.

1. Walk and mark first. Photograph every wall and ceiling you intend to open, with the homeowner present, before a single cut. This is your defense on every “that crack was not there” conversation.
2. Rough the new system alongside the old. The old pipe keeps working while you build. This is what keeps the actual water-off window down to hours instead of days.
3. Pressure test and get it inspected before you close anything. Never close a wall on an untested system, and never close one ahead of the inspector. This is non-negotiable and it belongs on the schedule you hand the customer.
4. Cut over, then replace the stops. Do the tie-in and change every angle stop in the same visit. Turning the system back on is when the thirty-year-old stops decide to fail.
5. Flush, then hand over. Flush the lines, check every aerator, and walk the manifold labels with the homeowner. Five minutes here prevents the callback that costs you an hour.

6. Price it and put it in writing

Quick answers