My wife and I are building a 4 season 21x36 Polytec greenhouse with 2
wall polycarbonate sheeting in East Tennessee. One of the many
problem (subject of another post) encountered so far is how to
insulate the base. The base consists of 6x6 treated posts with
treated 2x10s between. One side of the house is on a down slope that
leaves about 3 feet of exposed base. My wife wants to have "raised
beds" on the low side and tables sitting on gravel on the high side.
I'd planned to put styrofoam to insulate and black plastic to keep
water away from the wall. I'm not sure what order to do this. I'd
planned to have, from outside to inside, facia (probably metal), 2x10
walls, insulation, black plastic, gravel/soil.

Any constructive comments would be appreciated.

Thanks,
Harry