Do I need footings?

[Timmer]

Having only worked with concrete only for post hole construction, am not familiar with other concrete applications. I am planning to construct a garden shed (10' x 12') and would like to pour a concrete slab for the foundation. Will I need to make footings or can the slab just float above the compacted soil (with compact limestone)? Should I make a 4" or 6" thick slab?
Am in Minnesota so the ground can freeze down to 5' some winters.
:?

[Rich]

That's a tough one. In most cases I would say yes you should have something like a footing. That may be something simple like a thickened edge. Some of the variables to consider... if you are driving vehicles close to the it may or may not heave due to frost, if you have it near a home it may or may not heave due to frost, if it's on a slope it may or may not heave due to frost.
Sorry to make light of the situation, but that's about how predictable that heaving/expansion/contraction is due to freeze / thaw cycles. The best case would be to plan for the worst case. Sorry I can't give you more.

[mreynolds]

What is common around NW PA is pole construction with a slab poured in. This summer I built a 24x24 garage (frame construction) because I wanted to practice to build our house next summer (I know it sounds nuts, but I have never done this before). In order for me to put a footer in I actuall went down around 42 inches to ensure that the footers were below the frost line. The frost depth here is 36 inches. From there I laid 5 courses of block and then began to build. If I was doing it to be cost effective I would have done pole construction, drilled the postes, then place the slab inside with joints in the proper location to permit movement. It seems like if you build on top of the slab you would subject the entire structure to frost heave (5 feet sounds pretty deep). Is it possible to build on something other than a concrete pad, like a treated wood floor? :roll: