Matching Room Add Foundation with Main House

rweklund

What is the best way to match or alter a concrete room addition slab that is 6 inches lower than the main house slab, so that both areas will have the same base floor height (resulting in a seamless floor transition)?

AGWhitehouse

Concrete option: Form, lay down 2" of stone if desired, and fill with concrete to match.

Wood Option: lay down isolation strips (plastic or sill seal) under p.t. wood joists at 16" o.c. (2x6 at 5-1/2" and 3/4" plywood will make 6-1/4" total). Floor will be 1/4" proud with this setup, but that's no different than the transition of alot of floor finishes

Alternative Option: 2" of rigid foam, 3-1/2" 2x4 joists laid right on insulation at 16" o.c., 3/4" plwyood subfloor sheathing. Floor will be 1/4" proud with this setup, but that's no different than the transition of alot of floor finishes

__________________

Iconoclast

Just did this exact thing on my house.

Built up new slab to meet the existing house's floor level minus 3/4" to extend existing hardwood flooring.

We went with the concrete option but the other options mentioned by AG I also considered and would work as well.

rweklund

Thank you for your post. Its nice to know it can be done that way. BTW, did you use any stone/gravel for your base or did you go with 100% premixed concrete? Secondly, did you have to deal with any exterior doorways? I guess you could just make the doors smaller or raise them up via re-framing........

Iconoclast

Well I was supposed to have had a gravel base, that is what I requested but my contractor was a lazy sloppy worker and never put in the gravel - now it's too late obviously. But yes, I would do the gravel base if I were you.

And YES, have an exterior doorway as well. But the exterior doorway will be gone once it's framed in so it won't be an issue for us. I would think one could just raise the door as long as it's not a huge difference.