Concrete pad with footings for shed foundation?

[boxygen]

Slab on grade can be very sucessful in cold climates,however, it is grossly misunderstood by most. Three conditions are needed for frost: cold temps, cohesive soil and water. If you are missing one of those, no frost can form. With proper reinforcing. Well graded soil and insulation can eliminate the correct conditions. Frost is formed by ice crystals forming below the surface when the right conditions are present. The ice crystals pull more moisture through the soil from below through capilary action. If the soil is right and moisture is present it will continue to draw up moisture and grow the ice crystals. Typically this is done at a rock, because a rock is a better conductor of cold than the surrounding soil, that is why rocks migrate up through the soil "magically". That being said, If you build your building on a pile of crushed stone with insulation under it and proper surface drainage, you will never have frost. The moisture cant be pulled up through the large voids in the crushed stone and the rigid insulation will keep the cold from migrating down into the soil. Rebar, fibermesh and steel mesh and control joints are all still a must. Detailing the insulation and drainage can be difficult and unique to each site.

That being said, to do a slab on grade the "right" way will most likely be more expensive than a post and wood floor building. There is more to a slab on grade than backing up the concrete truck and unloading the truck and leveling out if you want it to last. You can keep the building off the ground better with a post system than a slab on grade. A course of block is a must with a slab. I think the post system will also be faster to build. If you pour a slab, order the concrete mix air entrained if it will be exposed to freezing temperatures. I dont know what Concrete costs in Ohio but my grandfather lives in Ohio and he said it was expensive and that is why they do so many block foundations instead of poured concrete. You can get it here in Maine with Admixtures like mid range water reducer and fibermesh for about $85/ cubic yard.

 

[ray66v]

Does anyone have experience using slabs with footings in the north, for buildings this size? When pouring slabs with footings, do you cut joints or leave it as one solid piece?

Yes, as long as local codes permit, you can do a slab on grade as described.

Yes, you want to saw it. Always cut it so the cut pieces are approximate squares. Cutting this in half, so you have 2 pieces, 10x12 will be fine.

I would put reinforcing wire in the lower 1/3 of the slab.

Rather than putting one course of block, I would recommend you pour a curb at the same time, and build your wall on top of that.

Or, build your wall right on the flat slab. Just use treated, on top of a foam draft sealer, for the bottom plate, and screw it down with blue screws.

 

[dave1949]

I don't think chickens and a wood floor would be a good mix. Why not build the shop floor out of wood and leave a dirt floor in the coop portion?

Did the old USDA standard design chicken coops have wood floors? I was thinking they did. Having cleaned a chicken coop a few times, I could never see how that was a great idea Plus the rat home you are creating below it.

Organic chicken raisers recommend a well drained dirt floor with deep bedding to minimize health problems.
Dave.

 

[Gary Fowler]

I dont know what is standard up North, but in the south, saw cutting of slabs is about every 15-20 feet. ON a 12 x20 you probably dont need any cutting to prevent shrinkage cracking. At most, I would only cut the 20 wide section in the middle I have a 30 x30 slab in my shop and no saw cutting at all. It has no cracks or crazing and it is a couple of years old. THe slab was poured in the early spring when the temps were about 40-50F so it cured slow which helped reduce the shrinkage cracking.

 

[Egon]

Nice information Boxygen.

A touch of reality never hurts.

 

[Ford850]

Thanks for all the feedback. I have more to consider now. To do a quality concrete job, it will cost more than a raised wood deck floor. Some of the concrete pads here do not have any stone base, due to the fairly well drained soil. I've had no problems with them but they are exposed pads and it doesn't matter if they are damp or heave from frost. To do this pad I will need more stone than I planned which raises the cost too. I do like the thought of the concrete though. I think a 4" slab with an 8"x8" or 10"x10" thickened edge would work. I planned to add at least one course of 6" or 8" blocks for a wall base/foundation. If I go the concrete route, it will have to wait until the ground is very dry to get a truck to the site.

 

[GE222]

The building I built in Southern Wisconsin was 42' x 48' slab on grade, with 14' sidewalls. The soil was heavy clay with quite a bit of rock. It was graded with a CAT D6. The slab perimeter is around 18" thick and about the same dimension wide, tapering up to a 5-1/2" slab thickness. Under the slab is crushed limestone.

The perimeter is full of rebar, and the mix had fiber added. The slab sawcuts were around 10' apart. It was build in 2006, and so far there have been no issues with the slab heaving.

The top of the slab is around 8-12" above the surrounding grade. The building also has 2' eves keeping the water away from the slab. Good drainage away from the building I believe is very important.

I considered a frost wall until I saw the $$$. Some of the extra dollars were due to the rock below grade.