In my area, a slab for a barn or shop is poured without a footing. Generally they start with a level spot and set up a 2x12 , rebar the slab area, and pour level to the top of the 2x12.
Why does a barn or shop not need a footing, but a house does?
People turn barns and shops into houses here quite often. ???
Thanks,
Todd
This is a "floating" slab, like a driveway. As long as the area beneath the slab doesn't collect enough moisture between the slab and frost free depth then they work fine. If moisture does collect there it stands a good chance of heaving. These are considered less important structures if there is an out of level or cracked slab. A good layer of gravel and sloping the grade all around and underneath to drain freely helps a great deal.
Quote from: Don_P on October 27, 2013, 12:42:10 PM
This is a "floating" slab, like a driveway. As long as the area beneath the slab doesn't collect enough moisture between the slab and frost free depth then they work fine. If moisture does collect there it stands a good chance of heaving. These are considered less important structures if there is an out of level or cracked slab. A good layer of gravel and sloping the grade all around and underneath to drain freely helps a great deal.
Thanks Don,
I was wanting to have a garage slab poured, and use above the garage for a bedroom addition for my cabin.
I was going to have several tons of gravel brought in first to spread out and tamp to help keep the slab well drained.
Also slop grad around the slab.
In a residence, and really in any building that is heated or of sufficient size that the slab cannot move as a solid unit and support the structure without breaking, I'd put in a footing to support the structure. That is pretty much the code read as well. That's part of why I was saying one way to do that is to pour footings and build or pour stem walls to support the building and then spread gravel inside later and pour a floating slab. The building is stable and the floating slab is independent of the structure. another option is a rubble trench foundation where a footing trench is dug below frost depth, with a drain to daylight, a filter cloth and drain are installed and the trench is filled with clean large gravel. a grade beam is poured (or thickened edged slab) and the building is set on top. Frank Lloyd Wright used this technique quite a bit. For precast foundations we have done something similar, also look at the permanent wood gravel foundations. Basically if water cannot collect and freeze and if you have bearing capacity, you've solved the heaving issue.