How feasible is it to mudjack or otherwise lift a slab on grade house to six inches above its existing grade?
I live in a less than 1000 sq ft home, built in 1948, with exteroir walls made of doubled 4" thick concrete blocks on a slab foundation–it’s heavy, and it sits on black clay. I don’t think it was built that high off of the ground to begin with, and over the years it has sunk until some parts of the slab are at grade. It’s in a desirable neighborhood, and I’m starting to think about adding on (a teardown would be cost prohibitive.)
It would be good to have the house at a higher grade. Could it be done, and how many times more would this cost over just stabilizing the foundation with piers? Needless to say, I’m not asking for a dollar amount. I’d just like a very rough idea–to know if this is in the scary money sort of range, if it would cost about twice the cost of stabilizing or less.
…Or would you rather have me ask how much houses cost per square foot?
Well, around here the task is done relatively frequently. It is quite expensive-ranging up to $150K. Alternatives I have heard is to turn the first floor into a basement, reinforce the walls and just build the house on the new second story. One unusual method I have heard of is to literally pour concrete into the house. If you really only need 6 inches, consider whether just filling in 6 inches on the slab will do. It means 7.5ft rooms (at least 6 in shorter than now), and the windows and outlets are closer to the floor than now, but it is sometimes done. The studs are protected before the concrete is poured. Another way is to use 2x6 joists and build another floor. punch holes in the wall for ventilation and you have a very small crawl space! People are always looking for a solution to this problem, but there appears to be no simple solution.
Well, $66/sq ft is scary money, but that is for raising the foundation three feet or more.
I may still ask about this when I ask for bids. When I asked about this before, a driven steel pier franchise said that they could take out the six inch variation in height that the slab also has. My thoughts are that if they can lift the corners that far then they may be able to do the entire slab without placing beams and using cribbing.
As an aside from the OP’s question about slab foundations, suppose you wanted to build a house that you knew would require periodic elevation for as long it existed? Say in an active flood plain where you knew that every 15-20 years a flood would add another foot of silt to the surrounding land. What would be the best way to build-some sort of platform on pilings?
I’d go with a conventional wood floor. These can be jacked up infinitely. It would be wise to check per the aggradation occuring over years time in that locale. Say, the river deposits 1 ft per year. In 10 yrs that’s 10 feet; one story. A better idea is to stay out of the floodplain.
Please remember that concrete can take compression, not tension. Most slabs have steel in the top for that, but not the bottom. Picking up the slab by the corners will put the bottom in compression, and cause it to fail.