Hi  All

I am doing a major expansion to a cabin and making a home of it.  I plan to add a wrap around concrete porch on 3 sides . The existing slab has a wrap of 4 inches of vertical rigid foam down to 2 ft depth.  The  ground here freezes 2 to 3 ft deep.  The contractor wants to drill the existing slab edge and insert rebar pins to link the porch floor to the main slab.  That would create a continuous thermal path to the slab and I am concerned that the floor around the edge of the house would get cold.  Also if the frost heaves the porch floor it would probably crack.  The porch floor has columns that support a roof to add to the problem.  If I dig down deep and install drainage around the porch  would it heave?  Could I trim the existing foam to the thickness of the porch anf keep the inside floor warm?  Is there any point to putting rigid foam  under the porch floor to keep the ground from frezing? 

Thanks, Walter