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Community and Q&A

Slab on Grade & Plumbing Distances

hem_wh | Posted in GBA Pro Help on

Hello! We would like to do a slab on grade foundation w/ radiant floor in climate zone 6. The slab will be insulated. One bathroom is about 35′ (in plan) from the mechanical room and where the other bathroom/laundry/kitchen are. Does this propose an issue for doing the plumbing lines below the slab? Thank you!

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  1. charlie_sullivan | | #1

    It can be done, but it's not great from either the perspective of providing convenience to the residents or that of energy efficiency. An great architect will be able to come up with a plan that meets the object that led to that distance while keeping the plumbing better consolidated.

  2. user-2310254 | | #2


    Are you building a tight house? Will there be code or higher levels of insulation under the slab and in the walls and ceiling? If you read through previous GBA posts on radiant heating, you'll often see that the experts, with some exceptions, are not enthusiastic about in-slab heating. (It's often a cost and comfort argument.)

    If you're building a tight house, mini splits can be a better choice and provide air conditioning when the weather is hot.

  3. Jon_R | | #3

    If you decide to use a radiant floor in a well insulated/sealed house, limit the tubing area. This will allow the warm floor feeling you are probably expecting.

    Heat pumps plus radiant slab floors are very energy efficient.

  4. Expert Member
    NICK KEENAN | | #4

    In addition to the other comments, if you have to run the plumbing 35' only run the drains under the slab. Run the supplies in the walls and ceiling.

    A drain has to drop a quarter inch per foot, so that's about nine inches of drop. May be something to consider.

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