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Rough-in plumbing: the stage of a renovation you only see once

Rough-in is when the pipes go into the walls and floor, before anything is plastered or tiled. In a concrete house it is the only time they are easy to reach. Every decision made here is set in cement afterwards.

This is the plumbing half of our bathroom and kitchen renovation plumbing work. Here is what it involves, so you know what to decide and what to ask for.

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What goes in at rough-in

  • Supply lines: the pipes that bring water to each fixture, cold and, if you will have a heater, hot.
  • Drain lines: the pipes that take water and waste away, from the toilet, the floor drain, the basin and the shower.
  • Vents: pipes that let air into the drains so they flow freely and do not pull the water out of the traps.

Decide these before the first pipe is cut

A plumbing layout for a small house, as the sheet draws it A plan of a small house with a kitchen on the left, a CR at the upper right and a bedroom at the lower right. A dashed water line runs from the water meter outside the left wall to the kitchen sink, and on to the lavatory and the water closet in the CR. A solid sanitary line collects the kitchen sink, the lavatory, the floor drain and the water closet, passes a cleanout, and leaves the house to a septic tank outside the right wall. A thin storm line runs from a downspout at the house corner, down the outside of the wall, to a catch basin and on to the canal. The three lines never join. A legend names each abbreviation. kitchen CR bedroom KS LAV WC FD WM CO ST DS CB to the canal WM water meter KS kitchen sink LAV lavatory WC water closet FD floor drain CO cleanout ST septic tank CB catch basin dashed: water supply solid: sanitary drain thin: storm drain DS downspout

Drag the drawing sideways to see all of it.

The sheet a rough-in follows: water supply dashed, sanitary drain solid, storm drain thin, and every fixture placed before a pipe is cut. Our guide to the plumbing plan reads it symbol by symbol.

The actual fixtures, with their spec sheets

Toilets differ in how far the outlet sits from the wall, and basins and mixers differ in where they want their pipes. American guides quote one standard distance. The only one that matters is on the sheet for the toilet you are buying, so choose it first.

Hot water, now or later

If there will ever be a water heater, decide which kind now. A single point or multipoint heater needs different pipework, and a hot line laid at rough-in costs far less effort than one chased into finished tiles.

Which pipe on which line

Supply in PPR, especially anything hot. Drains and vents in PVC. Our guide to PPR and PVC pipe explains why.

A valve for each fixture

A small shut-off valve at the toilet and at each basin means a future repair does not mean turning off the whole house. Many older houses here have none, which is why a dripping tap becomes a whole-house job.

Where the floor drain sits, and which way the floor falls

The floor has to slope towards the drain, and that is set when the floor is screeded. A drain in the wrong corner leaves standing water for the life of the bathroom. Pick a floor drain with its trap built in, for the reasons in our guide to the floor drain with a trap.

Before anything is tiled

Ask for the water supply to be put under pressure and left to stand before the walls are closed, and for each drain to be run with water. PPR joints are fused, and a sound fused joint does not leak, but the test is how you find the one that is not sound.

Then photograph every wall and the floor with the pipes showing, with a tape measure in the shot. Years from now, when someone wants to hang a cabinet or drill for a grab rail, those photos say where not to drill.

The mistakes that show up later

  • A shower valve set too deep or too shallow for the finished wall, so the trim never sits flush once the tiles are on.
  • Drain pipes laid too flat, so water sits in them, or too steep, so water runs off and leaves the solids behind.
  • No vent, which shows up as gurgling drains and a smell from the floor drain.
  • A toilet outlet that does not match the toilet bought afterwards.

Questions about rough-in plumbing

What does rough-in mean?

It is the stage of a renovation when the pipes are laid in the walls and floor, before anything is plastered, tiled or closed up. Supply lines, drain lines and vents all go in at this stage.

Do I need to buy the toilet and fixtures before rough-in?

Ideally, yes, or at least have the exact models chosen with their specification sheets. Toilets differ in how far the outlet sits from the wall, and the pipe in the floor has to match the toilet you will actually fit.

Should the pipes be tested before tiling?

Yes. Ask for the water supply to be put under pressure and left for a while before any wall is plastered or tiled, and for the drains to be run with water. A leak found now means remaking one joint. Found after tiling, it means breaking tiles to reach it.

Can I move the toilet or the shower in a renovation?

Usually, but the toilet is the hardest to move because its drain is the largest pipe and needs a steady fall to the main line. In a ground floor slab that means breaking concrete. Plan any move at rough-in, never after.

Renovating? Send us the plan

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Renovating a bathroom or kitchen?

Re-piping, moving fixtures and the rough-in itself are part of our renovation plumbing service. Send us the plan before the tiler arrives.

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