I'm building a new home in New York State. It will be slab on grade with radiant heat in floor. I'm going to run the domestic water supply (PEX tube) to each bathroom, sinks, toilets etc. in the concrete but inside of 1-1/4" PVC pipe in the concrete.

Are there any problems with this approach?

  • 1
    What's the purpose of using the pvc?
    – Edwin
    Jan 2 '14 at 8:13

I can see two things to be concerned with.

1) Is the 1-1/4" PVC pipe of sufficient size to permit you to pull out the old and replace new PEX tubing if that should ever be required in the future?

2) Make sure that the PVC pipe does not detract from the thickness of your slab to the extent that it would weaken the concrete and lead to a potential crack path. Cross wire mesh and re-bar in the concrete will help a lot but consider some additional thickness in areas where the pipe is embedded.


Be concerned about

  1. Rat & mount entry points.
  2. Bends, that make replacement of pipe in the future impossible.
  3. Thickness of concrete both above and below the 1-1/4" conduit pipe, along with any steel rebar discontinuities. Keep in mind concrete should flow freely around all steel, and steel wedged against your conduit pipe won't function as it should.
  4. Entry points for termites.

You are putting radiant heat (PEX) directly in the floor. As such I don't see any advantage to putting the plumbing PEX in a sleeve, and the disadvantages are being pointed out by other answers. If you are particularly paranoid about the plumbing for some reason, run double lines to everything and cap one of them at both ends to serve as a spare. In addition, you can wrap and tape sill seal sill seal around all the pipes at any point where there will be an expansion joint (it cushions the pipe just a bit if the concrete cracks and moves), and toss in a bit more reinforcing steel than the bare minimum that will be specified.

Wrap the sill seal around the pipe for about two feet (one foot either side) of planned expansion joints.

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