I have what used to be a carport, now a sunroom. The sunroom was poorly done, with pressure treated soles on the concrete, which are now nice and rotten. There are footing pours on the corners for the carport posts that were there. Question: To do this right, I need a footing poured so that I can also raise the floor to match the rest of the house. Can the footing be poured on top of the slab, or must it go down deeper and wider? Yeeesh.
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If it's becoming habitable space, and supporting a load, the footing has to go down below the frost line. You haven't mentioned where you live, but in 99% of the country, the frost line is obviously deeper than your slab.
Bob
Seattle. Not much cold weather!
Maybe 70% slab on grade is not all that uncommon. I wouldn't be suprised if this one couldn't be taken care of by floating a new slab over the old.
The clues "carport" and "sunroom" indicated a decent climate.
I just learned something new - PT will rot in the pacific northwest..
Excellence is its own reward!
The bigger concern is what is the slab on top of. I would not trust the slab to be on undisturbed soil or properly compacted fill and able to take the bearing pressure of the new walls. Since it was just a carport who knows how the base for the slab was prepared. cut it out and install new footings on a base that you know was right.
Thanks! Sounds like $$$$ however. Oh well, better once right than twice.