What Sort of "Foundation" for a Long Shed?

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Old 02-01-11, 08:51 AM
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What Sort of "Foundation" for a Long Shed?

Last year I bought a metal building that measures 12' x 31', but never managed to get it put up, partly because I couldn't decide on what kind of ground prep I needed. I need to get it built as soon as possible this spring, though, so am looking for some advice.

Front half will be for typical storage, lawn eqpt, bikes, etc. and will have a treated plywood floor. The back half will be used for animal shelter and supplies with only the dirt floor.

The area is fairly flat and does stay pretty soggy after a rain, so I was concerned about ground movement. I was thinking that a building this long would have a strong reaction to ground movement, so I wanted to find something that would be fairly stable but didn't require digging for full on footings. Any suggestions?
 
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Old 02-01-11, 03:25 PM
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The purpose of the foundation in metal building systems is to hold the building down in the presence of strong winds. Metal buildings are much lighter than wood framed buildings and will want to lift. You don't need a full perimeter foundation, but I can build a case for why one is desireable. What we would do as a minimum for a building with this footprint and a maximum eave height of 10' is a 2'x2'x2' pier under both of the main support columns and 12"x12"x2'D under each of the corners with #4 rebar cages in each. The total volume for those piers is only 24 cu.ft. or about 0.9 CY.

Take your time laying out the pier locations, verify that your layout is squared and keep the tops of the piers at equal height. Do that and your building erection time will be enjoyable. Don't do it and you will have earned all the frustration you will go through.
 
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Old 02-01-11, 09:12 PM
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Since this does not have what I would call main support columns, I suspect I should clarify and say this is more of the garden shed variety. I think the walls are only 7 ft high.

Perhaps I am making more of this than necessary, but I was concerned about it buckling somewhere as the ground moves. How much racking will something like this handle?

In its crudest form, I was thinking to level off the perimeter, lay some 2x, or maybe 4x treated lumber, flat on the ground and run some 3 ft. anchors down every several feet. If I can raise it a few inches and slope the surrounding ground away, I am hoping that it will stay dry enough below to minimize any gross movement.
 
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Old 02-02-11, 11:42 AM
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So, you are saying that what you have is a metal box kite. Are the structural members at least square tubing or just cold formed sheet metal?

Regardless of that, it's a safe bet you're going to have far more deformation caused by wind, snow, and/or ice loads than could ever occur from ground movement.

Good luck with your project.
 
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Old 02-02-11, 01:53 PM
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Exactly. But at least it is better than the little kite that is in the area right now. It has been through some fun times and is still standing. It's all sheet metal, but some of the more important members are heavier gage than others I've seen. Still, by the time I'm finished with it, I will likely add some wood structure in some places for additional wind resistance. I don't intend to do this over.
 
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Old 02-10-11, 04:55 AM
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First off, congratulations on your ambitious project. Second, do yourself a favor and do it right the first time.
I would go with footings and stemwalls with a concrete pad in the storage area. Use rebar to eliminate any distortion by ground movement. Make sure you are working on compacted soil, not loose fill.
Pick the brain of a local contractor. Most do free estimates and offer advice. (I know because we do it all the time)
Push some allthread into the wet concrete stemwall a minimum of every 18 inches. Leave it sticking up about 3-4 inches (see your building fastening details) because this is what your sillplate and building will be fastened to. Be sure that they are sticking straight up. Use 2 (one for each wall) at the corners about 3 inches in from where the building corner will be.
Sill plate? Use pressure treated 2X4. Lay it over the allthread and tap it to make marks. Drill these out slightly larger than the diameter of the allthread and then lay it in place.
Now you can use the allthread, a washer and a nut to fasten down the building. "Ping' the threads after you do the final tightening..( after the building is finished,) to keep the nuts from loosening.
A stemwall is, in my opinion, a must where the animals will be. Urine is corrosive to the metal. The concrete is also easier to shovel against when cleaning.
Good luck and have fun. Let us know how it is going and if you run into problems.

allthread is just threaded stock. You can cut the lengths you want with a hacksaw. Make sure you push at least 8 inches into the wet concrete. You can even put a nut on that end if you want to.
 
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Old 02-10-11, 05:19 AM
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I'd be leery of using allthread, it would be better to use foundation anchors/bolts. They come in several different lengths but the main thing is they are L shaped. It still has the threaded end but the angle at the bottom makes it harder for them to be pulled out of the concrete/mortar.
 
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