Understanding slab foundation

I’m a student still, bear with me. I’m in Arizona and almost all the houses here have slab foundations. I’ve noticed that the floor of the foundation is in line with the top of the stem wall except for in the garage. In the garage, the stem wall projects above the floor of the garage. Is this because the garage has a more shallow poured foundation? I’m trying to understand. Thank you!

Welcome to our forum, Karen.

I would want my wood/drywall wall higher so it doesn’t absorb moisture from the vehicles dripping and to keep flammables lower than the house floor…like 18" for any ignition point.


The garage floor may have been poured inside the foundation to slope the floor for drainage


They don’t have rain or surface water in Arizona. For drinking and other use they have to squeeze many, many cacti! :rofl:


Yeah, I missed that Manny, thanks. :+1:

Thank you! Does that mean the garage foundation is less shallow then the rest of the house then? Or is it just offset and deeper in to the ground?

So, in that case does Arizona make amendments to the IRC which requires positive slope away from the foundation?

I think Arizona also does a lot of tensioned slabs don’t they? OP, definitely look into those as you learn. The areas I inspect in don’t have them but I had a CE class once and the guy talked a lot about tensioned slab houses and I think he was from Arizona.

No they make amendments on the number of cacti that can be planted within close proximity to the structure! :rofl:

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Garage slabs are poured separate from the home foundation. It’s typically just a 4-6" slab, not part of the monoslab or stem wall. It’s usually also poured after the rest of the home is already under construction.
That’s why cracks in the garage floor are typically not a structural concern.
I do call them out if the cracks are becoming off-set from each other.


There are several ways to pour a foundation and garage floor.

Here is an illustration of two types of pours for a garage (not monolithic)

Here is a monolithic garage pour.

Here’s a pic of a slab and garage floor here in Arizona:

Screen Shot 2021-10-31 at 12.54.48 PM

The garage floor is sloped for drainage and you can see the slope when looking at the stem wall around the garage floor.

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