Foundation and slab questions
Owner/builder SFR new building in zone 5 (6200′ above Reno). On a 17% south facing slope with somewhat friable bedrock varying from 1′ to 4′ below ground level. 1000 sq.ft. garage slab on grade with stepped footing/stemwall foundation. 1200 sq ft two story house with stepped footing/stemwall crawlspace foundation.
The building inspector has already given the ok to drill into the bedrock and connect the stemwall directly to the rock where it can’t be dug with the backhoe.
The footing is 16″ wide, 7.5″ tall, with 16″x16″ steps about every 10′ or so to go down the slope. The stemwalls are 7.5″ wide and vary from 16″ to 48″ tall, the max height to avoid engineering.
Can this footing stemwall system be poured monolithic? With the footing forms having open tops? Was thinking it could be poured in lifts with the first pour/lift filling all the footing steps, then the footing, then the stemwalls in two or three lifts. I’ve seen contractors pour footing/stemwalls all at once but not on a slope with the steps. Seems like a good option to avoid the cold footing to stemwall joint in a seismic/high wind zone. Would have a concrete pump truck to do this.
It’s just kind of scary to try and get the slump correct. Helping my neighbor pour his slab in two parts on two different days and two different slumps made the work dramatically different.
On the slab want to put 1-1/2 of EPS underneath and then a 12″ square grid of #4 rebar. Want to be able to drive a 6500 lbs Bobcat on it and bring in some heavy machinery (10,000 lbs?) with a forklift. Was thinking of going to a 5″ thickness? The 12″ square seems good for the pour, so you can step in the holes while working it, compared to the 8″ woven mesh. Could this dimension go to 16″ square?
My neighbor completely eliminated the rebar in his slab just going with the small fiber reinforcing, but I thought this was only to control drying cracks?
Should I go with the budget Home Depot EPS? That does say it’s rated for under-slab. Or something with a higher PSI rating?
There is also some fill under the slab, up to three feet in depth. Should this be building sand, or should it be road base?
The only other thing that seems problematic is how do you set up a screed edge on the slab when the footing/stemwall is already poured? The stemwall will be up to 4″ higher than the slab, and slab is sloped to drain toward the garage doors. You could do the slab in two parts which would give you a center edge. But the edge at the wall is the issue. The only DIY info I’ve found is to hand trowel an edge during the first part of the pour. Seems like one of those things that’s going to be difficult on a first time, one time basis.
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