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Question DetailsAsked on 2/14/2017

How to plumb a bathroom in then poor concrete floor

Adding a bathroom on to a metal shop building. Want to put in plumbing and then poor concrete for floor

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2 Answers


I don't this is the forum to give a tutorial on underslab plumbing - if doing this yourself maybe buy the Black and Decker or otehr DIY book on plumbing for instance.

Specific recommendations -

1) test everything WELL - multiple tests - before concreting it in.

2) place the piping below the slab by 6 inches or more, bedded in compacted bedding sand - both to avoid the slab putting direct load on it, and also to make it easier to cut through the slab and fix in the future if needed.

3) if this is an addition to the building, assume the slab will move relative to the existing building - code requires a flexible coupling at the slab boundary if the piping passes from one building to the next unless the slabs are fully integrated. If totally new bathroom with no existing plumbing to the shop building, then bring in the piping from outside the existing building direct to the bathroom.

4) use compressible sleeve around the pipes where they come up into the slab so if it settles there is some give before the pipe breaks - usually asphaltic wrap is used on pipes.

5) concrete and copper do not get along - any copper piping HAS to be fully rubber or compressible foam wrap (seamless) wrapped where it comes through and for at least 3-4 inches above and a foot or so below the slab to prevent corrosion.

6) don't forget venting and a sewer cleanout right outside the slab - if you can put a 3 or 4" cleanout point on the sewer pipe "upstream" of the toilet and indoor to the building (but NOT in cabinet or vanity) that is helpful too - can eliminate the need to remove the toilet to rout out the line, and an exposed cleanout stubout in a shop-type building bathroom is not likely to be objectionable.

7) bear in mind if in an area with freezing conditions, you will have to maintain heat in at least the bathroom during the winter - and a freeze alarm which sounds inside the house might be useful too.

Any normal plumber will know these rules and other code requirements for underslab plumbing.

Answered 3 years ago by LCD



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