I am in the design phase for converting my south facing patio/porch into an attached greenhouse. The existing porch is post and beam (6X6's). The posts are bolted to a floating 6" concrete slab on grade without any footer or insulation. I intend to use all the existing porch wood for the greenhouse. I need to anchor the posts to a proper depth below the frostline. The existing slab would be the floor of the greenhouse. My question is how can I insulate the floating slab (and the new concrete pier/post foundation). Can I trench the perimeter of the slab to the frostline and install rigid board insulation vertically to grade? Will the insulation stand up to frost heaving?
Attached are pictures of the porch showing post and beam design and another of the corner post attached to the slab.
Any information is welcome. Thanks.