Expert: Daniel Humphrey - 9/25/2010

Question
We have a screened porch  that we are considering making a 3 season room.
The slab is very thick at least 5". The footings, I have no idea. We live in the
northeast. Is there any concerns we should have about expansion if we
enclose on this slab. ( we are thinking of big windows all the way around
would there be shifting issues from freezing and thawing).  

Answer
Dear Ellen,

If the slab has not heaved while exposed to the elements, then it will be fine covered. The problem is that the slab may have heaved in past winters but not enough to notice. But once you put windows in, any movement can be a problem of the framing is tight.

So take care when installing windows that you make the rough opening at least 1/2" larger all around to allow for frame movement. Doors should also have plenty of room around for shims, and trim that is screwed on so that you can adjust them if needed. For the interior finish, I recommend planed board and batten over 3/8" cdx plywood. Don't use any masonite type of paneling, since it will warp in the cold and will not deal with flex.

The frame itself can handle a little movement.

Good luck!

Daniel