I am unable to find a link, and IIRC this was reported 10 years ago or so. I recall an attribution to German designers or architects. I cannot remember where ex

I am unable to find a link, and IIRC this was reported 10 years ago or so. I recall an attribution to German designers or architects. I cannot remember where exactly it was reported, but I remember it as moderately plausible reporting, although not in a journal. A quick estimate with soil: Take a specific gravity of 2.7 gm/cm^3, a specific heat of 0.2 cal/gm-K, and 1 cal ~ 4.2J ~ 4.2 W-sec. For a cube 25 m (2500cm) on a side, if I am not mistaken this suggests a thermal inertia of about 3.5E10 W-sec/K. Now take a thermal conductivy of 1 W/m-K. For a slab of 25m x 25m, also with a thickness of 25m, we get a net conductivity of 25 W/K . Then 3.5E10 W-sec/K divided by 25 W/K gives 1.4E9 sec . Given 3E7 sec/year, that suggests about 47 years. Aka a 50 year time scale. Of course this assumes a low water table.