#21  
Old 01-16-2013, 01:42 PM
Faith In Virginia's Avatar
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Default Re: foundation depth confusion

One more try. you are correct there will still be some moisture in the center under the slab but not enough to cause heaves. (that is unless you built it on top of a spring)

There is nothing wrong with your #2 picture. There are many ovens here built on piers. Good idea...have at it. Just be sure that the pier footers are large enough to support the total weight of the oven and are below the frost line. If your going to build your piers out of block I would use two block per level then core fill them ( be sure to rotate every level) That will be steady as a rock and last a long time.

Have fun with your build!!!
Faith
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  #22  
Old 01-16-2013, 02:03 PM
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Default Re: foundation depth confusion

What about earthquakes? Just kidding. Our oven is on 6" slab on 6-8 inches of 1-1/2 gravel, block stand with 8" slab on top with oven and structure on top of that. We have used ours for about 3 + years and no movement, up down or sideways, until the earthquake comes. Mesh, rebar and core filling throughout. Do what is adequate for your area with a little overbuilding just to be safe.

That's my 3 1/2 cents worth.

Good luck !
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  #23  
Old 01-17-2013, 12:12 PM
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Default Re: foundation depth confusion

Ok i was emailed another post that also agreed with me somewhat but it seems to have been deleted from he thread. Anyway thank you all so much for all the thoughtful comments. I am probably going to do a slab with some extra drainage underneath and use no footings. Thank you thank you.
Ron
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  #24  
Old 01-18-2013, 07:38 AM
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Default Re: foundation depth confusion

You probably don't need another opinion but.......If you don't want any heaving, then place 2" foam insulation under the slab and at least 3' out around the parameter. It's a little expensive at about $22 a sheet from HD, but we pour a lot of floating slabs like this in Wisconsin.

~Aaron
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  #25  
Old 01-18-2013, 08:46 AM
Faith In Virginia's Avatar
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Default Re: foundation depth confusion

Aaron, I'm familiar with doing slabs that way, I have lots of family in Vermont. What would you do with the overhanging insulation around a high traffic area like a WFO? Pavers?
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  #26  
Old 01-18-2013, 08:47 AM
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Default Re: foundation depth confusion

Thanks Aaron. What does the insulation do? Does it compress to prevent the slab above from rising?

Also, do you place it between the slab and the gravel layer?
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  #27  
Old 01-18-2013, 01:08 PM
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Default Re: foundation depth confusion

Quote:
Originally Posted by Faith In Virginia View Post
Aaron, I'm familiar with doing slabs that way, I have lots of family in Vermont. What would you do with the overhanging insulation around a high traffic area like a WFO? Pavers?
We first cut the insulation to fit inside the forms and place the pieces around the outside after the forms are removed. We usually dig down around the edge, and slope the it down from the bottom of the slab and just backfill over it. How much we slope it depends on the situation, but for a wfo you would only need about 6" of coverage. With a 6" slab your about there anyhow providing you backfill close to the top of the slab.


Quote:
Originally Posted by ronwass
Thanks Aaron. What does the insulation do? Does it compress to prevent the slab above from rising?
The insulation keeps the ground underneath from freezing, and therefore also from heaving. They say ground will freeze at roughly a 45 degree angle inwards from the edge of the insulation, hence the need to extend it beyond the edge of the slab.

Quote:
Also, do you place it between the slab and the gravel layer?
Yes, the concrete is poured directly on top of the insulation.

Hope that helps,
~Aaron

Last edited by AaronTheGeek; 01-18-2013 at 03:24 PM.
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  #28  
Old 01-18-2013, 04:54 PM
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Default Re: foundation depth confusion

AaronTheGeek is spot on regarding the frost protection of foam insulation. Just make sure to get extruded polystyrene (closed cell and water proof) and not expanded polystyrene (open cell and water permiable) i.e. white bead board. And the 2# density has better compressive resistance than the 1-1/2# board. In the Dow brand the 2# is blue and 1-1/2# is gray.
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  #29  
Old 01-19-2013, 08:06 AM
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Default Re: foundation depth confusion

Quote:
Originally Posted by silvfox View Post
AaronTheGeek is spot on regarding the frost protection of foam insulation. Just make sure to get extruded polystyrene (closed cell and water proof) and not expanded polystyrene (open cell and water permiable) i.e. white bead board. And the 2# density has better compressive resistance than the 1-1/2# board. In the Dow brand the 2# is blue and 1-1/2# is gray.
Good points silvfox. We use Owens Corning brand. The FOAMULAR 250 (25psi) is what we use most of the time. The FOAMULAR F-150 (15psi) is what HD has around here, and I don't see why it wouldn't work for a WFO.

~Aaron
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