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Efficacy of laying insulation flat on ground around house?

  1. Nov 24, 2015 #1
    OK, sounds nutty in a limited short title, but...

    For a planned dome home in an area where average annual air temperature is 72 degrees, and thus steady state ground temperature at 20' deep or so stays within a pretty narrow range near that 72 degrees year round average above, and where house will purposely not have it's concrete pad or footings insulated so as to have earth, by design, be in contact as a heat sink in summer and heat provider in winter, how much would the following contribute to help that ideal work?

    From exterior edges of dome home extending outward 12' in all directions, there would be a 12' continuous deck surrounding the dome, laid flat upon the ground, that was made only of 4" polyurethane freezer panels. (These have galvanized metal on both sides with the 4" of polyurethane sandwiched in the middle. Assume no air or moisture infiltration between the bottom of them and the ground.)

    How much would that insulation set up help to dampen the hot/cold summer/winter temperature swings of the earth immediately below the concrete pad all along the outer edges of the dome?

    FYI, cost is not an issue or question here, these are used/surplus 50 cents a sq ft panels, and also the seamless installation and waterproofing and UV protection of exposed ends is not an issue either. Also, consider the color reflectance of the top surface as 'neutral', equally absorbing sun in winter and reflecting sun in summer, to take solar gain or lack of out of the equation, so as to be just looking at the air temperature seasonal swings affect on the earth below them.

    What I'm trying to get a fix on is, with this 4" of insulation extending out 12' in all directions away from the concrete floor atop the earth, how much might that insulation be helping keep that concrete floor nearer to 72 degrees compared to not having installed any such insulated decking?

    Appreciate any thoughts and/or suggestions to improve on above.
    Last edited: Nov 24, 2015
  2. jcsd
  3. Nov 24, 2015 #2
    This plan would give no noticeable improvement in the home's temperature variations. The time scale is too long. Temperature variations might be delayed a week at the most.
  4. Nov 24, 2015 #3


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    Staff: Mentor

    What are the average summer and winter temperatures? And is he house heated and air conditioned?
  5. Nov 24, 2015 #4
    Frost Protected Shallow Foundations (FPSF) employing below surface horizontal insulation
    wings outward from bldg is well accepted and basically same concept I'm exploring here.


    Specifically, how effective 4" of insulation (approx 24 r-value) extending 12' out on the surface
    would be in narrowing that ground temperature swing range under the dome pad that normally
    only narrows tightly at deeper depths as it approaches the average annual air temperature.
    Another way to ask is; How many feet of dry earth does it require to achieve an r-value of 24?
    And, yes, I understand that the large heat capacity mass differences of earth and insulation
    complicate any straight comparisons of heat flow projections based solely on r-values.
    Last edited: Nov 24, 2015
  6. Nov 24, 2015 #5
    I don't have summer/winter averages handy, but the cooling degree days are about twice the heating degree days.

    Average annual air temperature is 72 F, which I understand is best indicator of what the stable ground temperature will be at 5 or 6 meters down.

    It's what I'd like to maximize being closer tied into, with proposal of insulating ground surrounding structure, to then minimize heating and cooling loads, both of which will be available, if necessary.
    Last edited: Nov 24, 2015
  7. Nov 25, 2015 #6
    Can you tell us the location?
  8. Nov 25, 2015 #7
    West Texas
  9. Nov 25, 2015 #8
    Last edited by a moderator: May 7, 2017
  10. Nov 25, 2015 #9
    Last edited by a moderator: May 7, 2017
  11. Nov 30, 2015 #10
    As a suggestion, imo dampness would tend to accumulate in the volume downside and to climb from underground around into the dome _interor_ through trhe floor, counterfeiting the intended goal.
  12. Nov 30, 2015 #11
    A vapor barrier on the ground, beneath the floor, should lower risk of any moisture intrusion from below, if that's what you were thinking.
    Also, local environment is extremely dry year round, very low humidity, 10 inches rain annually and most of that runs off, not soaking in.
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