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.