Building on exist. sloping concrete slab
johntrev
| Posted in Construction Techniques on
I’m developing the ground floor basement/garage area (adding bath, BR, family room, about 600 sf) of a house in which the main living areas are on what is essentially the second floor. My problem is the existing slab slopes, about 10″ over the 23′ on which I’ll build.
I haven’t priced it out yet, but I’m thinking the expense of a new slab/foundation work may not be worth it, and I could just lay down sleepers and shim to level out the floor.
Yet if I do a new slab I can have greater head room (will be lucky to get 8′ otherwise), likely a more effective moisture barrier, perhaps more flooring options, and won’t have to dicker with the existing sloping slab. Either way, I’ll have some concrete work for the bath.
Any ideas? Thanks.
Replies
all i can say is 10" is a lot of shimming for sleepers. i'm guessing the concrete will give less trouble in the long run.
Hope this helps. Rich.
Rent a walk-behind concrete saw, about $150 for the day. Cut the existing slab up into rectangles that you can use as stepping stones, or give away. Start fresh with a level floor, it'll save you loads of trouble on the rest of the project.
-- J.S.
Thanks for the replies. I think you're probably right that starting fresh is the way to go.
I would look into lightweight concrete over the existing slab. This concrete is used on roof slabs over structural concrete to give proper drainage on commercial buildings. If I understand you, you need to level an existing slab, this is a simple way to do it.
Contact a concrete contractor as the concrete is pumped in.
Mike
John-
Are there footings under this existing sloping slab? If it's juts a 4" slab pour, you can't build on it anyway- you need footings to below the frost line.
Bob
Thanks for the reply. There are footings already.
I'm also concerned that if I break up the existing slab, I may undermine the footings. Any ideas?
Footings are supposed to go down deeper than the slab, so undermining shouldn't be a problem unless this whole structure is a very badly done bootleg job. Were the footings and slab done all at once in a monolithic pour, or did they first pour footings and stemwalls, and then after removing the forms pour the slab inside them? If it's monolithic, cutting the slab out with a concrete saw will get you the cleanest result with the least possibility of damaging the footings you need to keep.
-- J.S.