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Have an unfortunate "this is the only way this is going to work" situation with a DMV repair, resulting in the repair portion of the drain pipe, having to run 4 feet horizontally (yes, at the correct slope of 1/4"/ft) before turning up into the main vent stack...mostly above the gravel sub-grade and tapering into being completely within the 6" horizontal space where the concrete slab will be repoured. Question is, can 3" sch. 40 PVC pipe be directly embedded in concrete? Not covered by, or under, but directly embedded (concrete will fully encase 4ft of the pipe). Wondering if the heat of curing will warp/crush the pipe? I know horizontal stub-outs come through a concrete slab all of the time with no issue, but not seeing a lot of examples of horizontal embedding. I'm sure there are other ways to do this without the last-ditch option of embedding PVC horizontally in concrete, but those involve a 5-figure $$ removal of the entire basement slab and replacement of every single pipe.....just to get that 4' run of PVC encased completely in the gravel sub grade. The attached photo is a very poor rendition of what's going on here, not to scale, best a non-computer person could do! not to scale drawing

  • I have no idea if there are any 'code' restrictions, but in the part of the world I'm originally from, it would be standard practice to embed pvc waste pipes & pvc electrical conduit in the concrete floor slab of a house during construction. – brhans Sep 6 '16 at 13:06
  • It's not best practice, which is to keep plumbing below the slab to prevent cracking of the slab and damage to the plumbing from fasteners, etc. Concrete doesn't approach the high temperatures necessary to warp or soften PVC. – isherwood Sep 6 '16 at 14:28
  • DMV? you mean DWV I guess? – DaveInCaz Jul 12 at 14:48
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PVC pipe embedded in concrete should be fine under most codes I've seen. You'd need to sleeve something like black, galvanized, or no-hub iron pipe, but PVC and ABS are impervious on any reasonable timeline (~hundreds of years.)

You could have your inspector come through before the pour to check out your plumbing permit if needed.

And the diagram worked great, I think I understood exactly what it was conveying.

  • I guess to clarify....would the heat of the curing concrete deform the PVC? – tpcolson Sep 9 '16 at 18:34
  • I can't imagine it would, though I can't show you an equation to prove it. You'd need to get it up around boiling to deform, which is tough in a normal slab. – Joe Makes Things Sep 9 '16 at 18:36
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Thanks for all the replies! All the sleepless nights were for naught. 2 weeks after the pour, no crushing of PVC observed!

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