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Community and Q&A

Hydronic Garage Floor Layers

JoeM | Posted in Green Building Techniques on

Hi. I’m in the process of building a detached garage and have just had the stem walls poured. I’ve been looking and haven’t seen a schematic cross section relating to the layering of materials under a 4” garage floor that includes pex. In talking to my concrete guy he suggested eps foam with 6” wire mesh laying on top of the foam and 1/2” pex tubing zip tied with a spacing of 12” between runs. The garage is 24’ x 32’ and I’m figuring two zones of 300’ should be sufficient for the needs of melting snow under our vehicles in the winter. We’re in Idaho at 6200’ elevation. My questions are these. 1. Does the vapor barrier lay above the foam and under the wire mesh?  2. Do I need crushed rock under the EPS? How thick should my EPS be? I’m planning on a 3KW electric boiler to heat the slab sufficiently to melt snow from the undercarriage. If this has been talked about in another thread please direct me. Thanks, this is my first question in the forum.

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  1. JoeM | | #1
  2. dennis_vab | | #2

    How are you detailing the garage door and side door openings? That’s something that I have in mind for my garage slab that will be poured later this year.

    1. JoeM | | #3

      Two garage doors, they’ll both be insulated. Steel most likely as the wood doors are exxxxxpensive. Side door will be solid wood. I’ll also have high r-value windows, three. This is a two year project so I’m still working out how I’ll insulate the structure. Good luck.

      1. Expert Member
        MALCOLM TAYLOR | | #4


        I think Dennis was asking about how you intend to isolate the slab edge at the openings where it poses a huge thermal bridge.

        1. JoeM | | #5

          Malcolm, I hadn’t thought about that honestly. I’ll have 2 x 9’x .33’ of surface area at the garage openings and 3’ x .33’ at the door. Is there a method commonly being used presently? Maybe a steel grate over rigid foam to slow heat dissipation. It’s not a living space so I’m not overly concerned, the goal is to melt snow and ice from vehicle’s undercarriage and wheel wells. Thanks for bringing that issue up.

  3. Expert Member
    Akos | | #6

    If you are going to be using an electric boiler why not skip the hydronic bit and go with resistance wires? Saves space as there is no need to make room for a boiler and plumbing and a lot of cost.

    For thermal break by your doors you can use something like a composite 2x6 on edge or two composite deck boards. These are sturdy enough to drive over but have some R value. Make sure all the edges of the heated slab are isolated for any other concrete and no gaps between the rigid under the slab, this means a vertical insulation between the slab sides and the foundation as well. Concrete is a great conductor of heat, a couple of thermal bridges like that and you can easily loose half of your heat output to the great outdoors.

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