Newbie in NE Illinois - foundation question

[Alec&Elena]

Dear all,

This is something that we wanted to built for a long time.
The ground here is pretty frozen now, we are collecting information for the planned standalone corner install of 36" Pompeii oven on a 61X61" foundation.
What scares me the most at this stage is the need to excavate to 42" below the grade.
Maybe someone has a better idea for a cold climate?
What I had in mind is to put 4-6 concrete plugs (D12x42) anchor rebar to them and have 6" grade-level foundation over 3" of tamped gravel. Did anyone have any experience with this type of foundation?

Many thanks,
Alec

[timo]

Re: Newbie in NE Illinois - foundation question

I can only offer what I did up here in Grayslake, there are many knowledgable people here that can offer more specific details for best practices.

When I submitted plans to the building dept, they said a floating slab of 6" on crushed rock with rebar and all would be OK. Then they came back later and wanted me to dig the full 42" depth for frost footing.

It all came down to the height to width ratio. Since my build height wasn't much more than the width they settled on the original plans. The result? Since built, it hasn't moved in any slight manner. Mind you, we are talking about tons of crushed rock with perimeter drain tile to whisk any water away.

All I can say is for the soil and make up of my area, this has worked well. My build thread is here.It has a lot more detail about it all. I hope you are able to make it come to life. If you want to come and take a look some time give me a PM. Timo

[Lburou]

corner oven

In retrospect, my words offered poor advice....So, I take them back and recommend the quote below

I can only offer what I did up here in Grayslake, there are many knowledgable people here that can offer more specific details for best practices.



When I submitted plans to the building dept, they said a floating slab of 6" on crushed rock with rebar and all would be OK. Then they came back later and wanted me to dig the full 42" depth for frost footing.



It all came down to the height to width ratio. Since my build height wasn't much more than the width they settled on the original plans. The result? Since built, it hasn't moved in any slight manner. Mind you, we are talking about tons of crushed rock with perimeter drain tile to whisk any water away.



All I can say is for the soil and make up of my area, this has worked well. My build thread is here.It has a lot more detail about it all. I hope you are able to make it come to life. If you want to come and take a look some time give me a PM. Timo

[Alec&Elena]

Re: Newbie in NE Illinois - foundation question

Thanks for the ideas. I will check with the city, but I am more and more inclined to go with the "slab on legs" plan.
Got a call with a quote last night from a local concrete contractor. He actually proposed something like that (4 D12X42 "legs" and a 60X60X4" slab on top, rebared and anchored to the "legs" for $2300. Seems slightly obscenely priced to me...
Regards,
Alec

[Lburou]

Re: Newbie in NE Illinois - foundation question

Thanks for the ideas. I will check with the city, but I am more and more inclined to go with the "slab on legs" plan.
Got a call with a quote last night from a local concrete contractor. He actually proposed something like that (4 D12X42 "legs" and a 60X60X4" slab on top, rebared and anchored to the "legs" for $2300. Seems slightly obscenely priced to me...
Regards,
Alec

You're not going to say "no" to the contractor's trip to Hawaii are you?

Really, it can be done by ordinary people with a little help from their friends.

I hired a trusted carpenter to help me set the hearth slab forms, and a trusted mason to bring his friend to mix and pour & finish the concrete. Ask around in your circle of friends, you may hit the jackpot.

[dmun]

Re: Newbie in NE Illinois - foundation question

What I had in mind is to put 4-6 concrete plugs (D12x42) anchor rebar to them and have 6" grade-level foundation over 3" of tamped gravel. Did anyone have any experience with this type of foundation?

I think a slab with some sonotube legs protruding down is the worst of both worlds. These cylinders just give the ice lenses something to grab on to. You should either pour a reinforced slab on well drained crushed stone base, or you should dig down below the frost line and pour footings on undisturbed soil.

The theory of the slab on drained stone is that frost heave can only work if there is wet soil contact. The stone drains any water away from the slab.

[Tman1]

Re: Newbie in NE Illinois - foundation question

I think a slab with some sonotube legs protruding down is the worst of both worlds. These cylinders just give the ice lenses something to grab on to. You should either pour a reinforced slab on well drained crushed stone base, or you should dig down below the frost line and pour footings on undisturbed soil.

The theory of the slab on drained stone is that frost heave can only work if there is wet soil contact. The stone drains any water away from the slab.

Dmun is an extremely qualified individual, but I can't concur with his statements in this instance.

I think this can be a good idea, BUT you definitely need to be down far enough (below frost line) and I think the use of sonotubes is extremely beneficial as it doesn't give the earth a place to 'grasp'. An open hole filled with concrete has an uneven surface around the edges and I think that provides a place for frost to grasp and lift or do whatever it wants. The tube provides a buffer allowing the earth to move without moving the concrete in the tube. Of course, this is my logical side talking (and all my construction experience), but I have no degree (well, hard knocks master). Anyways, many things, bigger and heavier than a WFO have been built upon a floating slab.

I'm curious what the city would say if you asked the question about the footings.."Are you telling me I HAVE to have footings or recommending them?" I can't say that I've found building inspectors to be very helpful, since it usually seems to me that they ONLY answer the question asked. (of course there are few good inspectors, but they aren't as common as power-tripping dolts, IMO.)

[mn8tr]

Re: Newbie in NE Illinois - foundation question

Depending on what you vision is for the finished product you might want to consider a stand alone steel stand rather than stone or brick foundation. The three legged idea is also good. Renting a power post hole auger could make quick work for footings.

[Alec&Elena]

Re: Newbie in NE Illinois - foundation question

Seems like it all boils to talking with City inspectors.
I wonder if anyone had any experience with the slab+sonotubes type of foundation.
Sonotubes are required in this area for attached decks. They have to go at 42" or deeper.
Many thanks for all good suggestions and replies,
Alec

[Tman1]

Re: Newbie in NE Illinois - foundation question

uhhhh, experience is 15 years of building sheds weighing anywhere from 1000 to 3500 pounds...

[Lburou]

Re: Newbie in NE Illinois - foundation question

A & E, A block wall with slab is much easier to form when it comes time for pouring the hearth slab than a structure with legs. What is it about a wall and slab that you object to or are concerned about?

dmun doesn't use many emoticons, is matter of fact (maybe even seem opinionated), but when it comes to these matters, he has earned my trust.

I just poured my hearth slab. I had originally made the block stand to fit a small barrel oven. Well, when I realized a dome oven would better serve us, I had to make the hearth wider than the block stand. Then is when I learned first hand the head ache associated with making forms that will hold a lot of weight and stay suspended in mid air until the concrete cures (28 days).

Forms for suspending concrete in the air are material and labor intensive. Forming over a good block stand is much easier to manage than the sonotube design. Just my two cents -back in my box now.

When you are past the design phase, it can go pretty fast if you have the time and money. Too many options make decisions unnecessarily difficult sometimes.

Good luck to you

[Neil2]

Re: Newbie in NE Illinois - foundation question

"I think a slab with some sonotube legs protruding down is the worst of both worlds."

I agree with Dmun. If you are going the sonotube route, take them down below frost level and "bell" them out at the bottom. Do not connect them to a slab at grade.

If you are going the floating slab route (which I think is adequate in any but the worst soil conditions), pour a 4 inch reinforced slab on 4 inches of granular material. This granular layer should ideally be provided with drainage. The subgrade should be uniform, either native soil or well compacted fill - avoid areas where there may be differential settlement.

Only if your local building department insists would I bother with full depth footings.

As for the additional form work in building a suspended slab on piers, in my case I think it was worth it;

[dmun]

Re: Newbie in NE Illinois - foundation question

This has been much discussed here. Be sure to see the picture at that link. I would only do the slab with sonotube drops if your building inspector demands it. Otherwise I think it's a lot of work that may well be counterproductive.

[Tman1]

Re: Newbie in NE Illinois - foundation question

.. and I would add, only do the tubes if you go below frost. If you don't your wasting effort.

[Neil2]

Re: Newbie in NE Illinois - foundation question

"only do the tubes if you go below frost."

And "bell" them out at the bottom to resit uplift. This is quite simple. Just use a long bar and widen out the bottom of the hole to about twice the diameter.

I would only use sonotube if I were continuing them up as piers to support the structural slab. If supporting a block wall, I would just go the floating slab route.

A note about frost heave. This is indeed capable of vertical shifting of structures, and this could be a major concern with structures like decks, houses or garages. But for a stand alone oven, unless your soil is unusually susceptible, minor vertical movement can easily be accommodated with a well reinforced slab on grade. Unless it tilts so far that the pizza slides out on its own.