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Need footing for stud wall/joists on garage slab?

S

sal

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Jul 17, 2017
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medford
I am designing a floor that will be built directly on top of a garage slab by installing 2x12s nailed to a sill plate fastened to the slab with tap on screws. There will be a bathroom on top of these joists.

do I need a footing at the sill plate where the joists/ bathroom wall are bearing on the garage slab?

is the slab enough to support this load or is a foundation Wall required here? Perhaps just a thickened slab at that point?

Although why do we need anything if the garage slab can support the load of a car?
 
This sounds like a conversion of a garage to habitable space. Garages have been built with a lesser footing than is required for habitable space. That's not to say that this holds true with your particular property but if that is true you may need to improve the footing. Now there is a wrinkle to understand. Many jurisdictions have adopted relaxed regulations for Additional Dwelling Units. Sometimes there will be a dispensation allowing an existing, lesser footing for a garage that is being converted to an ADU.
 
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Actually this is for new construction. Trying to save costs by not creating basement or crawl space where the bathroom would be on top of garage slab
 
Every garage conversion I've ever designed used sill plates attached to the slab at 4' spacing in order to distribute the load over the slab, not just to the slab edges, avoiding the need for adding footings to the existing foundation. Check your local jurisdiction's acceptability.

If it's new construction, why not just insulate the 2' perimeter under the slab, or vertically at the garage's stemwall face? No need for a wood floor, sleeper plates and all that.
 
Most garage slabs are "sloped" and this could create an issue with framing the floor level. Assuming the exterior walls studs are sitting on a sill plate that is anchored to the stem wall you could set new joists on that sill plate and then add a ledger on the opposite side and make the floor system level without even touching the slab. Just a thought.
 
Does he mean Tapcon?

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I wouldn't accept without an engineers sign off.

Although, it seams they have some approvals.......for something......some heavy sifting through the info here.

 
Sounds like you want to build a platform for a floor of a bathroom on top of a slab. If the platform is supporting the walls of the bathroom and the walls are not supporting anything else you can put the platform directly on the slab.
 
We have seen this where the bathroom pops out by a couple of feet into the garage. It is easier to just support it on the garage than to have the jogs in the foundation. Same as Rick, if it is not carrying roof loads we are fine with it.
 
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