Slab/plan review and questions
I’m building a small home in Phoenix AZ with the ideals of a “Pretty Good Home” in mind and an overall goal of net-zero. So I’m trying to adopt as many existing designs as possible — one such being the principles behind the foundation design found in the Dept Energy “Builder’s Guide” to “Hot-Dry” climates (attached). I do have some practical questions about all this, though.
First, I’ve also attached the floor-plan of the house (oriented North), because it matters a lot. Note that there are extensive (concrete) patios covering the entire North and West sides and half of the South. Not shown in the (gravel) driveway covering the entire East wall.
Also critical to my questions is that this house will be built using Universal Design (ADA) principles, as well, and that means zero clearance thresholds throughout. So no steps or bumps or anything anywhere at all in this entire plan.
Given all that:
1. The foundation design for Phoenix recommends rigid foam on the edge of the foundation. I can see this with the “free” half of the South wall and the East wall, but how does this come into play with the extensive area covered by the patios? Does the foam just go up to the underside of the patio? Or does the patio just butt against the foam? And in that case, what happens at the doorways, where there will be a zero-clearance threshold?
2. The foundation plan also has the grade roughly 4″ below the top of the foundation. This will be strictly true only on the half of the South wall that’s traditionally exposed. The rest will either have a patio or a driveway butting against the slab/foundation. How is that handled? Is it okay that “grade” will be flush with the slab (even assuming the patio and driveway are sloped away)?
3. And this set of questions isn’t strictly “green building” related, but it’s related to the rest of my questions. How do foundation/slab plans given to the contractors doing the grading/pouring handle zero-clearance thresholds? Are the patios 1/2″ higher than the slab (to account for the exterior door thresholds and 1/2″ thick tile inside)? Or is the slab just inside of the walls 1/2″ lower, since having the patios higher would result in the patios butting up against the exterior wall, not the foundation? And I guess the shower room would just be 2″ lower than everything else?
As you can see, these are some pretty fundamental and basic questions… but ones that, I guess, are so low-level that I cannot find any answers to them. So in addition to any answers (gratefully accepted!!), I’d also like references to any resources (books, websites, videos, etc) that actually answer questions exactly like this.
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