#11  
Old 03-28-2011, 06:27 PM
Peasant
 
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Default Re: Footers or Slab

The base slab would transfer weight to the center pier via the concrete and rebar. In addition, I plan on (overkill) dividing the stand with a center divider. That divider would transfer weight from the hearth slab to the base slab.

I have done a lot more thinking this evening and going back and forth but am now leaning towards a full foundation again. While I think the piers will work, I am not sure I am willing to take the gamble even though it would be FAR simpler and less costly.
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  #12  
Old 03-28-2011, 06:54 PM
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Default Re: Footers or Slab

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Originally Posted by BeanAnimal View Post
The base slab would transfer weight to the center pier via the concrete and rebar.
Really? The force at the center of the slab would be up, not down. And in that case, the way you'd increase the load capacity beyond rebar would be post-tensioning, I think.

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Originally Posted by BeanAnimal View Post
In addition, I plan on (overkill) dividing the stand with a center divider. That divider would transfer weight from the hearth slab to the base slab.
In this case, the center pier becomes useful, but there's no point to doing either, IMO.

If you did do a full perimeter footing and foundation, the foundation slab becomes obsolete. I would build the stand either as poured wall or standard mortared CMU construction and maybe beef up the hearth slab, but there is zero reason you need a foundation slab with a full and proper foundation. It's exactly like a house at that point.
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  #13  
Old 03-28-2011, 07:18 PM
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Default Re: Footers or Slab

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If you did do a full perimeter footing and foundation, the foundation slab becomes obsolete.
True. I did this, and have a pressure treated floor bolted to brackets on the foundation walls to support my wood storage. One less thing to reinforce, mix, pour, and float.
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  #14  
Old 03-28-2011, 07:28 PM
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Default Re: Footers or Slab

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Originally Posted by splatgirl View Post
Really? The force at the center of the slab would be up, not down. And in that case, the way you'd increase the load capacity beyond rebar would be post-tensioning, I think.
It would depend on the design of the slab. The slab would have to be rigid enough to transfer the load. If the slab is not strong enough, them the center pier becomes a point load. In the same fashion, if the slab is not strucuraly sound and only has 4 corner supports, they are likely to cause the slab to fail if any of the corners move.

Quote:
If you did do a full perimeter footing and foundation, the foundation slab becomes obsolete. I would build the stand either as poured wall or standard mortared CMU construction and maybe beef up the hearth slab, but there is zero reason you need a foundation slab with a full and proper foundation. It's exactly like a house at that point.
Yes like a house The block (or poured) walls could rise all the way to the hearth slab and the base slab is simply a floor and not structural.

I need to pour a floor for the wood storage area and will need a ledge for the brick or stone facade. I could of course use the wider foundation block to create the ledge, but still need a floor. I will likely end up just pouring a 4" flour over the whole thing with enough rebar to prevent cracks. Maybe overkill, but on a small structure like this the foundation slab would tie the 4 walls together, more insurance against the poor drainage and frost jacking

I dread the thought of the added hassle, but I think I will sleep better. I still have a week or two to make up my mind though...
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Old 03-28-2011, 07:31 PM
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Default Re: Footers or Slab

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Originally Posted by dmun View Post
True. I did this, and have a pressure treated floor bolted to brackets on the foundation walls to support my wood storage. One less thing to reinforce, mix, pour, and float.
I do have about 36 sqaure feet of expensive pavers that we decide not to use for our fire pit cap stones
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  #16  
Old 03-28-2011, 07:31 PM
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Default Re: Footers or Slab

I live in Western Michigan and grew up in Central Maine. Not wanting to worry about what Mother Nature might throw my way, I put the full foundation under my oven. Dug down through 4 feet of clay. Poured a 1 foot thick footer to support the walls. Cement block to grade and 4" slab on top of that. Everyone that saw the build told me that I was crazy. I told them that I agreed. I rest well knowing that frost will not likely topple the oven. On top of that, I was able to practice my masonry skills, which were non-existant, while building the block wall that is now hidden under ground.
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  #17  
Old 03-31-2011, 10:07 AM
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Default Re: Footers or Slab

all great points and a good read as I am having the same dilemma with my layout for my oven build...I was actually talking to an engineer friend of mine and he mentioned a floating slab 16" thick ---he said that for gas stations and garbage bin areas behind your local grocery stores thats all they do......heavily reinforced with re-bar of course and he mentioned adding a couple of inches thicker towards the outside edge.....and 2" of polystyrene insulation underneath!
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Old 03-31-2011, 12:30 PM
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Default Re: Footers or Slab

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and 2" of polystyrene insulation underneath!
Sounds like frost-protected-shallow-foundations to me. If you can't take the structure down to the frost line, bring the frost line up to the structure.
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  #19  
Old 03-31-2011, 02:13 PM
Peasant
 
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Default Re: Footers or Slab

I have looked at that page several times over the last year or so and similar pages.

This is the applicable image:


But my concern is still the highly plastic and expansive clay soil. It is very tempting to try for a project like this, but I just don't see how it will work due to the poor (total lack of) drainage under the 6" gravel layer that is beneth the foundation.

A parking slab at a filling station and a 6x6 oven are very different
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  #20  
Old 04-01-2011, 09:20 AM
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Default Re: Footers or Slab

If you go the pier route, do not tie an at grade slab to the piers.

This will not contribute to the bearing strength. In frost susceptible soils in particular, a tied slab will tend to move and put stress on the piers.

Last edited by Neil2; 04-01-2011 at 09:24 AM.
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