We are going to be building a 16x24 cabin with a loft and will be using sonotube concrete forms for the footings. How far apart should they be spaced, how far below the frost line (10 inches), and how far above the ground would you recommend?
Also, we are plannig on renting either a bobcat with an auger (50hsp) or a mini skid-stear (20hsp). Our soil is really stoney so we're wondering which one would probably be best? Would the smaller one be sufficient?
The spacing of the sonotubes is determined by your foundation design, specifically how big the beams are going to be. The tradeoff is that larger beams cost more, but the spacing on the sonotubes is greater. The required size of the tubes depends on your soil conditions, and the load on each support. You need to do some soil sampling before you can size the tubes, unless you go with minimum sizing from the local building code.
Required depth of the footings is typically based on local building code, check with your local building inspector. Often the building code will dictate the sizing and connection details for all structural elements, best to check with the building inspector. If there is no building inspector, or you are not required to pull a permit, it is generally safe to design to the building code for your state or province.
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