Plumbing decisions to make before a kitchen or bathroom remodel

A remodel is one of the few times your walls are open, and that window closes fast. Whatever plumbing decisions you put off tend to get decided for you by whatever’s easiest once the drywall’s back up. Better to settle them now.

Are you moving any fixtures?

Moving a sink a foot or two is usually simple. Moving a toilet or a shower drain is a bigger deal, because the drain has to keep the right slope to the main line and often needs its venting reworked to match. On a slab foundation, that can mean breaking concrete to relocate the drain, which turns a bathroom refresh into a much bigger job. Decide where fixtures go early, before the floor plan gets locked in around the old drain.

A sink usually just needs its supply and drain extended through the wall cavity. A toilet or shower drain runs on gravity, and there’s only so much slope you can add before the drain runs too deep to tie back into the existing line at the right height. If a designer or contractor is pushing a layout that moves the shower drain, get a plumber to look at the slab and the existing line before anyone commits to it.

While the walls are open, deal with the old pipe

If your supply lines are galvanized steel or polybutylene, an open wall is the cheapest chance you’ll get to replace that section. Ripping the drywall open again later just to swap pipe costs a lot more. Galvanized pipe in older homes covers what to look for if you’re not sure what’s behind your walls.

Matching valves and trim

A new shower valve has to match its trim, meaning the handle, escutcheon, and diverter. These are sold as a matched set by brand and can’t be mixed later. Pick between a pressure-balancing and a thermostatic valve before rough-in, because the valve body itself gets set in the wall. Swapping valve types after the fact means opening the wall again.

Add fixture shutoffs while you’re in there too, one at each sink, toilet, and appliance connection, even if the old setup didn’t have them. It’s a small add during rough-in and a real help the next time anything needs service.

Special fixtures need decisions now

• Island sinks need venting, either a standard vent that runs up through the roof or an air admittance valve, which is a mechanical vent that fits under the cabinet. Which one works depends on your layout and what the local inspector allows, and it has to be decided before the island’s plumbed.
• A pot filler or ice maker needs its own water line, planned before the wall closes.
• A bigger tub, body sprays, or multiple shower heads use a lot more hot water than a standard setup. Check whether your water heater can keep up before you commit to any of them.
• A gas range needs a gas line run to the new location if it’s not already there.

Permits and inspections

Most remodels involving new plumbing need permits and inspections, and requirements vary by city. Check with yours before work starts. An inspector typically wants to see the rough-in before the walls close, so build that inspection into the schedule.

How the timing works

The plumber does the rough-in, meaning the pipes and valves that go inside the walls and floor, before drywall goes up. Everything gets tested, then the walls close, then the plumber comes back later for finish work: faucets, the toilet itself, trim kits, the parts you see and touch.

Order your fixtures before rough-in starts, not after. The rough-in has to be positioned to match the exact valve, faucet, and drain kit you’re installing. Late fixture orders are a common reason a remodel stalls, waiting on a part that should’ve been on site weeks earlier.

If you’re already thinking about replacing old pipe while things are open, our repiping page walks through what that job usually involves.