expansion options for under a wall

[garyarp]

I have a 4 season porch 16 x 16 on post with frost footings it is attached to our home on 2nd level.
We have a larger concrete slab under this addition that I would like to build a 3 season porch on 16 x 16 directly under this. fully enclosed with 8 windows
It is a floating slab & will not be heated.
what are my options for expansion so upper porch doesn't move or crush my new windows do to the frost heave. on sandy soil.
any suggestions appreciated

 

[3onthetree]

If your upstairs 4 season rests on proper frost footings, then it should not be moving to crush what you infill below. Down below, the slab can move, especially if not on a gravel base (however sandy soil drains well), but I would imagine it would most likely settle rather than heave.

 

[ConCretin]

It really depends on how much frost movement you actually get in the slab below. Some structures move more than others depending on proximity to existing buildings, soil conditions, drainage, etc. You could shoot a few elevations and then check it a few times throughout the winter to get a sense of how much movement you get.

If frost movement is modest, I'd probably incorporate some kind of receiver channel at the top of the new lower walls that allows for some upward movement. You could hide it with some kind of trim detail.