What plumbing questions matter before a bathroom remodel?

Whether a fixture moves is the single biggest plumbing question, because it decides the scope of the whole job. Swapping a toilet, faucet or vanity in the same spot mostly reuses the pipes you already have. Relocating a toilet, shower, tub or sink means new drain, vent and supply lines, and that is a different project.

Sort every item on your wish list into one of two piles:

• Same spot: new toilet on the existing flange, new faucet on the existing supply lines, new vanity that ties into the existing drain.
• Moving or adding: shifting a toilet to make room, converting a tub to a shower (see tub to shower conversion plumbing), moving a vanity down the wall, adding a second sink or a bidet.

A drain is not like a supply line. A drain works by gravity, so it needs a continuous downhill slope, and every fixture needs a vent so the trap keeps its water seal. Moving a drain far from where the vent connects can get complicated fast. Our page on drain pipe slope explains why you can't just push a drain sideways, and it's the reason a "small" layout change sometimes turns into cutting the floor open.

Then check the room around the fixtures. The International Plumbing Code, a model code published by the ICC, says a toilet, lavatory or bidet "shall not be set closer than 15 inches (381 mm) from its center to any side wall, partition, vanity or other obstruction." It also calls for "not less than a 21-inch (533 mm) clearance in front of a water closet, urinal, lavatory or bidet to any wall, fixture or door." Phoenix adopts and amends its own codes, so treat those numbers as a planning check, and confirm the current rule with the city or your plumber before you commit to a layout.

One more layout question to ask early: will the new fixtures fit the existing rough-in? A wall-hung toilet, a freestanding tub or a walk-in shower with a linear drain each need framing and drain positions that a standard layout doesn't. Buy or at least choose the fixtures before the plumber roughs in, so the rough-in matches the actual product's spec sheet.

Permits follow the same line as the layout. Like-for-like replacement is generally exempt, and relocation is not. The City of Phoenix building code lists plumbing work that does not need a permit, including "Replacement of water closets, valves or fixtures with new valves or fixtures complying with the water conservation requirements of this Code, except that a permit shall be required for the relocation of any valves, pipes or fixtures."

Read that carefully. It exempts replacing a fixture with a compliant new one. It does not exempt moving, adding or re-piping anything. The city's own text also says that if a concealed drain, water, waste or vent pipe becomes defective and has to be removed and replaced with new material, that work is treated as new work and needs a permit and an inspection. So if a plumber opens your wall and finds a failed pipe, the job may change category mid-project. For the full breakdown, read do I need a permit to remodel a bathroom in Phoenix.

Inspections matter as much as the permit. Phoenix's code says a rough-in inspection is required for sewer, drainage and vent piping, and for water and gas distribution systems, before they are buried or concealed: "A rough-in or underground inspection is required for all sewer, drainage and vent piping, and for all water and gas distribution systems prior to their being buried or concealed." The same section also requires a final inspection once everything is set and "operating or ready to operate pending final utility connection." In practice that means the walls stay open until the inspector signs off, and your schedule has to leave room for that.

Questions to settle before demolition:

1. 1Which parts of my plan need a plumbing permit, and which are exempt?
2. 2Who pulls the permit, the plumber or the general contractor? Get the answer in writing.
3. 3Does the remodel also trigger building or electrical permits? Those are separate. This page covers plumbing only, so ask your contractor.
4. 4When is the rough-in inspection, and will the walls stay open until it passes?
5. 5Who is responsible if an inspection fails, and who pays for reopening a wall?

Gas piping, if any is part of your home's layout, needs a licensed pro and a permit. Don't treat it as a DIY step.

### Pipe material and age

You need to know what is behind the wall before you cut into it, because a remodel disturbs old pipes. Tightening a supply connection or moving a valve can stress a pipe that has been quietly corroding for decades. Ask your plumber to identify the material of your supply lines and drain lines before demolition, not after.

What to look for:

• Galvanized steel supply lines. These corrode from the inside and restrict flow. See galvanized pipe problems.
• Polybutylene supply lines. An older plastic that many homeowners choose to replace. See polybutylene pipes, should I replace them.
• Old copper with pinhole leaks or green crusting at joints. Worth a closer look before you close a wall.
• Cast iron or older drain lines. Slow drains and odors around a bathroom can point to more than a trap issue.

Where you can see pipes, in a garage, a water heater closet, under a sink, or through an access panel, take photos and show your plumber. Where you can't, a plumber can check for hidden leaks and moisture using non-invasive methods. Our page on how plumbers find hidden leaks covers what those methods look like.

This is the moment to decide whether to replace the bathroom's supply lines while the wall is open. Access is easiest now. The plumber may also tell you the old lines are fine and should stay. Either answer is useful, so ask for it in writing so the contractor's schedule and scope match.

### Shutoffs and the water-off plan

Know where every shutoff is before anyone swings a hammer. Your remodel will need water off at least once, likely several times, and an old shutoff that won't close is a discovery you want to make on day one.

Start at the main. The International Plumbing Code calls for a full-open valve "On the water distribution supply pipe at the entrance into the structure." Locate yours and turn it off and on once. If it is stuck, leaks at the stem, or won't fully close, ask the plumber to replace it before demolition. Then check the individual fixture stops. The same code calls for a shutoff "On the fixture supply to each plumbing fixture other than bathtubs and showers in one- and two-family residential occupancies," so your toilet and sink should each have their own. Our page on how to shut off water to a fixture walks through it.

Two code details worth passing to your contractor: "Access shall be provided to all full-open valves and shutoff valves." So don't let a new wall, cabinet or tile job bury a valve without an access panel. And because tubs and showers don't get their own stops in that model code, a shower valve replacement often means shutting off the whole house or the branch. Plan for it.

A simple water-off plan for the project:

1. 1Test the main shutoff and each fixture stop now, and note which ones fail.
2. 2Decide which stops get replaced with new, quarter-turn ones before the new fixtures go in.
3. 3Ask how long the water will be off on demolition day and on the day the new fixtures are connected.
4. 4If it's your only bathroom, plan where the household will shower and use a toilet, and for how many days.
5. 5Confirm that water is back on, and that every connection is dry, before the plumber leaves each day.

### Water pressure

Check pressure before you buy expensive fixtures, because high pressure shortens their life and low pressure ruins the shower you're paying for. A cheap gauge on a hose bib gives you the number in a minute. EPA WaterSense's own instructions: "Attach a pressure gauge to a hose bibb, the cold-water faucet for the washing machine hookup, or a cold-water faucet on the first floor."

Here's what the EPA says about the range. Its technical sheet notes that "Most U.S. plumbing codes require pressure-regulating valves (PRVs, also called pressure regulators) on domestic systems where the pressure of the supplied water exceeds 80 psi." It also says "WaterSense recommends incoming service pressure to be between 45 and 60 psi to ensure efficient use of water and proper system function." If your reading is above that, ask whether the home has a working regulator, and whether it should be replaced or adjusted during the remodel. Our page on what water pressure should be goes deeper.

If pressure is low, don't assume the new showerhead will fix it. Low pressure at one fixture is often a clogged aerator or partly closed stop. Low pressure everywhere points to the main, the regulator or the pipes. Find out before the wall is closed. Some premium shower systems, like body sprays and rain heads, need more flow than a standard supply line delivers, so check the manufacturer's requirements against your actual numbers.

### Fixture choices

Pick fixtures with the plumber's input, and look for the WaterSense label. The EPA says "Design improvements have allowed toilets to use 1.28 gallons per flush or less while still providing equal or superior performance." Its faucet page says labeled bathroom sink faucets and accessories use a maximum of 1.5 gallons per minute, compared with a standard flow of 2.2 gallons per minute. And WaterSense showerheads must use no more than 2.0 gallons per minute, where standard showerheads use 2.5. EPA has also released a draft specification that would lower the faucet maximum to 1.2 gallons per minute, so check the current label criteria when you shop.

Before you order, ask:

1. 1What rough-in dimension does this toilet need, and does my drain match it?
2. 2Does this shower valve need a specific pressure or depth in the wall?
3. 3Is the drain assembly included, or does the plumber need to source it?
4. 4Do I have the manufacturer's installation sheet on hand before the plumber arrives?
5. 5What does the warranty cover, and does it require licensed installation to stay valid? Keep the receipts and the model numbers.

DIY is fine for like-for-like swaps that don't touch pipes inside the wall. Replacing a faucet on existing stops, changing a showerhead, swapping a toilet seat or flapper, or setting a new toilet on the existing flange with new supply line and wax seal are reasonable homeowner jobs if you're careful and shut the water off first.

Call a licensed plumber when any of these are on the list:

• Moving or adding a toilet, sink, shower or tub.
• Any drain, vent or supply piping inside a wall or floor.
• A permit and inspection are required.
• Gas piping of any kind.
• Old galvanized, polybutylene or leaking pipes.
• A main shutoff or regulator that doesn't work.

Before the demolition, bring this list to your plumber and contractor:

1. 1Are any fixtures moving, and does the drain and vent layout support it?
2. 2What permits are needed, and who pulls them?
3. 3What are my pipes made of, and should any be replaced while the wall is open?
4. 4Do the main and fixture shutoffs work, and will they stay accessible?
5. 5What's my water pressure, and do I need a regulator?
6. 6Do my chosen fixtures fit the rough-in, and are they compliant?
7. 7When are the inspections, and what does the schedule look like?
8. 8What does the warranty cover on parts and labor?

Answer those and the demolition surprises get a lot smaller. HQ Plumbing & Air offers 24/7 service, is licensed and insured, gives upfront pricing and offers free estimates, so bring us your plan and we'll walk through the plumbing side before you start.

Many of these questions come from the most common bathroom plumbing mistakes. If a bidet seat is on your list, check what it needs first. Our guide to the different types of bidet toilet seats covers the water and power each type calls for.