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Thread: Rough-in for concrete over PVC DWV

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    DIY Junior Member jmprTL's Avatar
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    Default Rough-in for concrete over PVC DWV

    What is standard practice at the rough-in stage for PVC DWV piping that penetrates a slab floor? In particular, how are vents and drains terminated in (or above or below) the slab before the concrete work is done?

    Are all drains/vents brought through the slab and left projecting above the level of the concrete, a foot or so? (Presumably toilet drains are then cut off to finished floor level.) Or is there some standard practice that leaves the piping at or below concrete level at rough-in, and then the piping is extended through the slab after the concrete work and structural framing are completed?

    I'm an amateur with some experience with under-slab DWV plumbing but in the past have used what must be non-standard approaches to this question. (I believe I'm adequately informed/experienced with pipe sizing and pipe layouts including under-slab practices, and can satisfy local building codes.)

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    DIY Senior Member dlarrivee's Avatar
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    Quote Originally Posted by jmprTL View Post
    What is standard practice at the rough-in stage for PVC DWV piping that penetrates a slab floor? In particular, how are vents and drains terminated in (or above or below) the slab before the concrete work is done?

    Are all drains/vents brought through the slab and left projecting above the level of the concrete, a foot or so? (Presumably toilet drains are then cut off to finished floor level.) Or is there some standard practice that leaves the piping at or below concrete level at rough-in, and then the piping is extended through the slab after the concrete work and structural framing are completed?

    I'm an amateur with some experience with under-slab DWV plumbing but in the past have used what must be non-standard approaches to this question. (I believe I'm adequately informed/experienced with pipe sizing and pipe layouts including under-slab practices, and can satisfy local building codes.)
    Most drains will simply be proud of the finished concrete elevation.

    Bath tubs and showers I would box out the area for the p-trap and allow myself to adjust the trap when the tub/shower is set.

    Toilets I would pad the outside of the pipe to allow the hub of a closet flange to reach below the elevation of the concrete, but that depends on what type of flooring you plan to use. I would use an inside pipe-cutter to adjust the height if it wasn't quite right.

  3. #3
    Moderator & Master Plumber hj's Avatar
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    we do the complete drain/vent system prior to pouring the slab so the entire network can be water tested and approved at one time.

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    DIY Junior Member BenWara's Avatar
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    I just purchased a house with an unfinished basement that was roughed in for a bath. They used 2x4s for make a box above where the shower line was. I just had to break the wood out and dig down. It is a horizontal line that is just capped. Other houses I looked at used a plastic box type deal. Considering that you will end up removing it anyway I wouldn't spend more that free 99 on it. for the stool they brought a three inch line up about 4 inches higher than it needed to be. they wrapped a bunch of sill gasket around it and didn't glue it in. For that pipe i just wiggled it out, unwrapped the gasket and put it back in for now. I'm in the process of finishing it now.

    for my light plumbing work i didn't have to worry about it but you might ask the inspector if you will have to do a gravity test. I'm pretty sure the builder had to. He put and inspected sticker on my vent that comes out the slab for all that is worth.

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