Kitchen and Bathroom Remodel Plumbing

Supply lines are forgiving. They are small, they turn easily, and running new water to a different wall is rarely the expensive part of a remodel. Drains are the opposite. They need continuous fall and they need a vent, and in most layouts that vent has to reach a stack or the roof, with an air admittance valve as the approved alternative in some spots. This is why a vanity can usually slide a few feet for very little while a toilet moving to the opposite wall rewrites the budget.

The floor decides the rest. In a house over a crawlspace, or a bathroom sitting above an unfinished space, a plumber can get underneath and move a drain in a morning. On a slab the same move means cutting the concrete, trenching, repiping, and patching before the tile setter can start. Bring the plan before demolition and you get the price of each option while both are still on the table.

Every fixture has its own rough-in numbers and they are not interchangeable. A toilet drain sits at a set distance from the finished wall, and the finished wall is not the framing once backer board and tile go on. A shower valve has a depth range tied to the thickness of the tile assembly, so the valve gets set after the tile detail is decided rather than before. A freestanding tub with a floor-mounted filler needs its supply and its drain placed to that exact tub, which means choosing the tub first.

Kitchen islands are their own problem, because the sink is nowhere near a wall to vent through. Depending on the layout the answer is a vent loop run under the floor or an air admittance valve, and which one is acceptable is worth settling before the cabinets are ordered. Shower niches, linear drains, wall-hung toilets on in-wall carriers, and body sprays all add rough-in that has to happen while the wall is open.

Most remodels around here happen in houses with a mix of materials. Galvanized water lines, polybutylene, early CPVC, and cast iron drains all still turn up, and they behave differently when you cut into them. Shutoff valves that have not moved in twenty years often will not seat again once they are closed, so the plan assumes replacing whatever has to be shut off to do the work.

While the walls are open, a partial repipe costs less than the same work later, because there is no drywall or tile to open and patch. If the house still has failing supply material, or pressure drops whenever two fixtures run, that is the moment to price repiping the affected side against doing it later through finished drywall. The same goes for a cast iron stack with soft spots. Adding a second shower head or a set of body sprays raises demand too, so the supply sizing back to the water heater gets checked rather than assumed.

Remodel work that changes drain, waste, and vent piping is usually permitted work, and permitted work gets inspected. The altered drain and vent piping is capped and filled with water so every joint can be checked under a standing column, which is the hydrostatic plumbing test the inspector is there to witness, and new water piping gets a plumbing pressure test that has to hold while the connections are walked. None of it is closed in before that.

That inspection sits between demolition and tile, which is the part homeowners feel. The rough-in has to be witnessed before backer board and drywall cover it, so the tile setter's start depends on when the inspector can come. A second look happens at trim-out, once the fixtures are set and running. Your local building department decides which parts of a remodel need a permit and how the test is run, so that is confirmed for the address before a schedule is promised.

The plumbing on a normal kitchen or bath remodel is not one visit. If a drain has to move under a slab, that underground rough-in comes first, right after demolition. The top-out follows once the walls are open: new drains, vents, and water lines in the walls and ceiling, plus the shower pan and valve work the tile setter needs finished before starting. Trim-out comes last, after countertops, tile, and cabinets are done, when toilets, faucets, sinks, tubs, and disposals go in. Some remodels need all three visits and some only two.

Because of that order, fixtures have to be bought early even though they are installed last. Nobody can set a rough-in for a tub, a shower valve, or a vanity that has not been chosen yet. In a one-bathroom house, or a rental with bookings on the calendar, the sequence is planned around how long the room is out of service, and the trim-out visit is the one worth protecting.