Features of a California slab foundation. What are they?
What features are in a no-basement slab foundation for single-family homes built in California, and what needs to be shown on the foundation prints, to satisfy both plans reviewers and the contractors that form and pour the foundations?
I am asking this about the class of slab foundation that is done on a lot with reasonably flat topo, where the foundation slab has thickened edges, maybe drops for room or garage stepdowns, curbs around the garage, maybe shower drops, footings under partitions and bearing walls integral to the slab, and more.
A slab-type foundation. Not one with stemwalls, deep grade beams, piers and beams, and all the stuff we do when going onto a steep hillside lot. Just a slabber. The edge thickenings might step a little to deal with a little terrain, but again, I’m just looking for what happens in a slab poured monolithically. In the big state with the big stiff codes and tight plans review.
I am looking to see what goes on, because I am participating in a dialog on the website forum where we discuss Chief Architect software, which is used to design and draw house plans. Chief’s tools for addressing monopour slab foundations is weak and needs to be improved.
For reference and to get a common terminology, I have included a sketch.
Replies
I've always used 16" high
I've always used 16" high perimeter and 12" wide 'footings' that slope up to the 4" slab. Thickened slabs in the middle were like 12" deep w/ sloped sides to the slab. I used this in the NW where I didn't have to worry about going down to frost line (which e.g. garages weren't required to do so).
Down here in SoCal, it is similar ... maybe not so agressive ... A friend did similar to my description above. He used fiber reinf. concrete instead of WWM, though. I think they still stuck 2 or 3 #4 bars around the perimeter (and thickened sections under bearing walls), though. Personally, I'd do the WWM and the #4s in this neck of the woods.
What's w/ the forum? I hope like heck I'm not your only responder. It takes many to make a forum, right? Bump
That sketch seems to follow the "rules" for "matt" slabs they way I was taught them ages ago.
Here in my bit of central Texas, that'd be a no-go with any muni with an adopted building code, as it would not address having 12-18" of contact in undisturbed soil. Here in this riverine area, 2' turn-downs to make a 'waffle' slab is much more common (if with a thin thin thin 4" slab all-too-often spanning that.
What's funny to me, is that you address in yout OP that this only makes sense on reasonably-level sites.
Yet, you can go over to Austin and no one will change the tract-plan slab drawings, even with 5' or 6' of drop on site. Which means you can see formwork using a 2x4 on the high side and sheets of plywood on the other, and there's seldom ever any additional fill brought in, so they just glob it full of concrete. Usually with little regard for how 4 or 5 extra yards of concrete might change the foundation dynamics. But, after all, concrete is the ultimate wonder material, spans gaps with the strength of crazy glue, inherently watertight, and always overpriced <G>