Building a raised floor over slab on grade
I’m about to kickstart a renovation project on a small barn – there was a previous attempt to convert it into a carriage house and unfortunately I’ll be gutting it and starting over given shoddy prior work.
The current floor is a slab on grade with drains in the middle of the 4 stalls plus a center aisle. I believe those drains The stalls are separated from the center aisle by a 4-5″ concrete lip. Rather than trying to demo all that concrete I am planning to instead raise the height of the floor above the lip (plenty of ceiling height left in the barn).
My plan is to follow the advice from the “no-mold finished basement” FHB article. I’ll lay 1″ EPS rigid foam and 2 layers of 1/2″ plywood. I’ll lay the rigid foam directly over the existing drains (should I bother capping the drains?). Call that Floor 1.
To raise the floor I was planning to lay some 2×6’s or 2×4’s down as floor joists over the plywood to raise the floor height above the lip and then top with 3/4′” ply as the new, raised subfloor (Call that Floor 2).
1) Does that plan make sense?
2) Should I be concerned about creating an air gap between Floors 1 and 2?
3) Additionally, will 1″ Owens Corning FOAMULAR 150 EPS rigid foam have enough compression strength for my application?
Happy to provide more detail if my situation is not clear enough. If geography matters I’m up in Maine – thanks!
Replies
Before you do anything, you had better find a way to permanently block those drains.
It sounds complicated and labor-intensive. A good concrete demo crew could have those curbs and drains out in a few hours at which point you could pour a 2" topcoat and be done with it.
Do you know if there is a vapor barrier under the concrete? Do you know where the drains go or is there a chance that could backflow under your new floor? What's the use going to be?