Here is a section of my planned slab/wall junction. The plumber suggested the drop in the rigid board under the slab, with the fill cover, because he says it is easier to work on top of fill than foamboard. He actually wanted it down far enough, with enough fill on top, so he could run all his drains atop the foamboard, in the fill layer. That would have put the foamboard down about 16″ under the slab. I thought this a better compromise. What do you think?
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I like it.
Like you, I try to work with my subs, but it isa impoirtant to remember that they cannot be allowed to drive the whole design. Too many cooks...
Excellence is its own reward!
Mr. Micro, I've got my Stupid Hat on this morning. Where is the plumbing/drain line? In the 2" of sand? Under the foam? Whole slab is foam underneath, not just the edge?
Being dumb,
Joe H
I would like to know why you would overhang the mudsills over the exterior of the foundation. And, does the whole slab sit on rigid?
The whole slab sits on rigid. The mudsill overhangs so I can have that sheath-hang detail and bring my shingle siding finish down below the rough floor line. I don't like nailing into concrete.
4-1/2" of bearing is more than OK for the walls. The house was designed with 2x4 exterior wallframes, but we must use 2x6 because of energy codes here.
The plumbing is all under the rigid now, in this concept. We'll have to poke a few holes in the foam slabs as we are placing them over drain stubs. There are just a few, and the water supply lines will all come from overhead.
I guess I am really asking whether it is more convenient for mesh placement, PEX tube tie-on, and slab pour, to bury the rigid under a little layer of coarse sand, or whether to place it immediately under the slab.
Mr. M, The sand on vapor barrier (which your foam will effectively be) supposedly turns into a lake. I can't say where that info came from, but that's what I remember. Maybe the foam manufacturer would have an opinion, but I think it's usually foam right against the slab.
My thought is hidden foam is more likely to be damaged than if it is on the surface.
Joe H
One would guess,with your water lines coming in from the top side you are located some place warm. If it were my home, I would run the soil lines, just like all the other soil lines, OK, maybe just a tad deeper, and I would also run my water lines underslab, just my 3 cents worth. Regarding the sand, I would put the sand on top of the foam bd, though I prefer ABC ( sand , rock and gravel ), for I feel it gives better compaction. If you have a good base underneath all this, ie type soils you are building on, I don't care what you name your slab, it will do just fine. Note: as long as it is finished properly, with good weather conditions, on your side during the pour. Best of luck Jim J
What you effectively have here is a floating slab. This has no tie in to the footer and any movement is going to reflect internally. Sorry. Pour design. Not structurally adequate.
regards
mark
Quittintime
Where did he say this is structural?.
Excellence is its own reward!
No mention of structural that I saw, either. However, I'd set some dowels, if only to keep the floor slab from "bumping" the foundation beam in the case of any future movement. Dowels would also help keep the slab from moving higher if there is any uplift. Which is all just MHO.
If the slab is using radiant heating, the thermal break is not that big a deal (at least not in the energy calculation programs I use--the mass of the slab increases effective R value).
Another way to detail it would be to use a wide, short foundation beam, then set the floor slab over that, leaving 4-4 1/2 for the wall framing, as per the detail as drawn. (This is basically a "plank" floor system, which is not seen in residential construction very often.)
One other item that caught my eye was the nailer for the "skirt" sheathing. I'd like to see some seperation (like bituthane) or the use of PT for the ripped down nailer. But that's probably more my bias from living in a damp climate where what doesn't rod mildews :) . . .
Hi Piffin
He doesn't say it's structural, and in my saying "it's not structuraly adequate" I am talking about in itself. I.E. without any loading produced during or after construction. The plan indicates it's for a house. To propose to "balance" a slab of any sizeable area on rigid board/ sand and compacted fill without any tie in to foundation is asking for trouble. ( in my opinion )
regards
markQuittintime
I see the point if there is a chance of unstable soils and settlement or heaving.
Excellence is its own reward!