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FPSF with hydronic floor heating in garage and house

Coop54 | Posted in Building Code Questions on

So …..I plan to build a new home in Zone 6A area of Minnesota.
The home is a box, 50×40, single story, with a 500 sq ft garage within the box.
I am using a frost protected shallow foundation product called (Mono Slab EZ forms). It took some convincing to get the local building official to accept the product but, he did. 
However, he has come back and said “that because the he thinks that someday, someone might turn off the in floor hot water heating loop in the garage, and that the garage now needs to be considered unheated”. This means of course that there is a required separation between the heated and unheated areas requiring an internal footing that is not needed. Can anyone provide an argument for or against this comment?
P.S. when I head to Florida in the winter,  I will not be setting the thermostat to 64 degrees (the required monthly mean temperature as per R403.1.1)

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  1. user-2890856 | | #1

    I have yet to see a model code that includes , " What If " . The garage is designed and being built as heated area , what someone may or may not do in the future should not affect your pocketbook

  2. Expert Member
    Michael Maines | | #2

    I'd side with your inspector. Homes are required to have rooms automatically heated, but there is no such requirement for a garage, and most people do not heat their garage, so it is highly likely that the garage foundation will fail due to frost heaving at some point in the future.

  3. Expert Member
    Peter Yost | | #3

    For better or for worse, codes ignore the occupant contribution to building performance. I can see the both the reasoning and the problems that arise from this approach.


  4. Expert Member
    Peter Engle | | #4

    All is not lost. The IRC provides prescriptive requirements for FPSF in conditioned spaces. It doesn't prohibit them for unconditioned spaces; it just doesn't have a cookie-cutter design tool. The IRC defers to ASCE 32, which is an engineering design guide for a much wider range of FPSF, including for unconditioned buildings. Your foundation form people should have their own engineering data for using them in unconditioned spaces. They may also have guidance for using them at the critical transition between conditioned and unconditioned spaces.

    If you intend to set your thermostat well below the 64 degree design temperature that the IRC requires, you should bring this up with the EZ form people as well.

  5. Jon_R | | #5

    The unheated FPSF designs are the better ones anyway (less thermal bridging).

  6. tommay | | #6

    Why do you want to use radiant in a garage? Unless you are using solar hot water which will maintain the heat while you are gone. Why not put in conventional baseboard or a modine type heater. Then you can do it after the inspector leaves, if there are issues, and then take it out when you sell and leave.

  7. Coop54 | | #7

    Thanks for replying. The 50'x40' slab is all heated with radiant in slab heating with 2" Amvic panel or Crete-Heat insulated R-10 panels under the concrete on a single plane. One of the thoughts behind this design was to be able to convert the garage to living space in the future. I guess I could call the space a hobby room? Then fight with the tax auditor!

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