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Thread: Replacing water line under slab - best type of pipe?

  1. #1
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    Replacing water line under slab - best type of pipe?

    I've had to trench into the concrete slab of a 1958 vintage house to replace the sewer line. The water line is exposed by doing this. I figure that I may as well replace that part of the water line too. The old water line is 3/4 inch copper. What's the best 2019 vintage pipe to use? Copper again?

    Under the yard near the house is a 1958 vintage shut off valve for the water line. (A plumber advised me not to try using it.) I want to remove this valve and replace the water line from just upstream of the valve to the point where the line comes up from the slab inside the house. So the new line will connect to the existing copper line in the yard.

  2. #2
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    PEX is the way to go.
    It's never too late to have a happy childhood.

  3. #3
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    Pex in PVC conduit so it can be pulled and replaced when needed. To replace 3/4" copper you need one inch pex.
    Bill D.

  4. #4
    The old copper has lasted 60 years. I don't think you will be around in sixty years, so why not go back with copper? Remember there can be no joints in either kind of pipe under a slab.

  5. #5
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    My copper pipe rotted out about 5 years ago, and I replaced it with 3/4" PEX.
    It was cheaper by far then the copper, I was told by the wholesaler it will never rot; another plus, is that in this earthquake zone, there's enough looped underground that any seismic upheaval won't bother it.
    Shark bit on the interior PEX to copper line, and a special fitting at the meter, and good to go.
    Young enough to remember doing it;
    Old enough to wish I could do it again.

  6. #6
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    PEX would be my choice. I've been replacing copper with PEX now for sometime...acid water really does a number on copper pipes. I pity a future owner here as our addition had to be done in copper because a local ordinance at the time prohibited PEX. (that's now off the books when they modernized their code only a year after we built) and even with the acid neutralizer, there's still some degradation expected. PEX is so easy to work with, affordable and is a great solution for in-slab work. That's what's used these days for in-slab hydronic heating, as a matter of course.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  7. #7
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    I'd contact a few local plumbers and see what they use/recommend.
    My granddad always said, :As one door closes, another opens".
    Wonderful man, terrible cabinet maker...

  8. #8
    I would recommend checking with the local inspector or code enforcement authority (especially on the joint between old and new). Codes and cities are particular about what they allow underground on the supply side. What they think is far more important than what folks on a woodworking forum think

  9. #9
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    Quote Originally Posted by Bruce Wrenn View Post
    Remember there can be no joints in either kind of pipe under a slab.
    Right where the old copper line enters the slab, it connects under the slab to pipe that goes up into the wall and feeds an outdoor hose bib. I'd like to get rid of the under-slab connection, but still have the outdoor faucet.

    The most convenient plumbing would be to feed the hose bib with a connection to the water line that is in the ground just outside the foundation - or put the outdoor faucet on a vertical pipe that comes up from the ground instead of out of the foundation. What's a good way to insulate this type of plumbing to prevent freezing ? (in southern NM).

  10. #10
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    Quote Originally Posted by Bill Dufour View Post
    Pex in PVC conduit so it can be pulled and replaced when needed. To replace 3/4" copper you need one inch pex.
    Bill D.
    What happens where the end of the water line comes up through the slab? Is there a joint in the PVC conduit where it transitions from being under the slab to above the slab?

  11. #11
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    Quote Originally Posted by Stephen Tashiro View Post
    What happens where the end of the water line comes up through the slab? Is there a joint in the PVC conduit where it transitions from being under the slab to above the slab?
    I meant conduit in the slab only. just to provide a pull path when needed.

  12. #12
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    If copper lasted this long, I would use copper.

  13. #13
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    Quote Originally Posted by Stephen Tashiro View Post
    Right where the old copper line enters the slab, it connects under the slab to pipe that goes up into the wall and feeds an outdoor hose bib. I'd like to get rid of the under-slab connection, but still have the outdoor faucet.

    The most convenient plumbing would be to feed the hose bib with a connection to the water line that is in the ground just outside the foundation - or put the outdoor faucet on a vertical pipe that comes up from the ground instead of out of the foundation. What's a good way to insulate this type of plumbing to prevent freezing ? (in southern NM).
    I can't image frost is too deep in NM. But you don't want your hose bib freezing. Options: feed from inside using a frost proof hose bib, feed it using a yard hydrant from outside the house, heat trace it or insulate it (only recommended for very brief (hours) of freezing. I presume your meter is out at the street and quite shallow? In any event, check with your plumbing inspector and utility. Yep, use 1" PEX to replace 3/4" copper and use full flow fittings if possible.
    Last edited by Ole Anderson; 07-15-2019 at 10:16 PM.
    NOW you tell me...

  14. Another vote for PEX. However, it does expand and contract slightly lengthwise, so run it inside another pipe like PVC and leave a little slack. Pex is great because it can be curved and bent (in wide radius) around corners and fed through walls etc. I replaced all the pipe in our old farm house all pex for the intake and all PVC for the waste and drains. PEX was a dream, no cutting and soldering or gluing. I would suggest you use crimp fittings because sharkbites are still unreliable. ( a buddy works for a restoration company. They get 4 or 5 jobs a year due to failed sharkbite type fittings.) I used the copper rings and I think they are still the best although a bit slower to use.

  15. #15
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    Quote Originally Posted by Perry Hilbert Jr View Post
    Another vote for PEX. However, it does expand and contract slightly lengthwise, so run it inside another pipe like PVC and leave a little slack. Pex is great because it can be curved and bent (in wide radius) around corners and fed through walls etc. I replaced all the pipe in our old farm house all pex for the intake and all PVC for the waste and drains. PEX was a dream, no cutting and soldering or gluing. I would suggest you use crimp fittings because sharkbites are still unreliable. ( a buddy works for a restoration company. They get 4 or 5 jobs a year due to failed sharkbite type fittings.) I used the copper rings and I think they are still the best although a bit slower to use.
    No fittings under the slab. And no need to put it in a sleeve, you are overthinking it.
    NOW you tell me...

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