We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember jim
saying something like:

but won't there be a huge thermal bridge straight down into the earth
at the bottom of the wall spoliing any meaningful storage of heat - in
other words acting as a constant heatsink - straight into the ground?

Jim

some, but you need a bit of integral calculus to calculate it..

I'd still guess it's a factor big enough to scupper any "thermal mass"
usage of existing walls....

Well, just ask somebody who's had it done. From what I heard, it worked
well.