Ok I'm new here. My wife and I have a 10 acre plot at 9000 feet in Utah. We have a dwelling, a septic system, a water system, and solar power supplemented with a generator. We want to build an outbuilding (as in,no permit) to increase our living area. The outbuilding will be 12 x 16 (+/-) adjacent to our existing deck. I am interested in all suggestions, but at this point it is time for the foundation. I like the idea presented in this forum of a gravel base for concrete forms and I used a similar concept for the deck construction; no gravel since the weight of the deck is less than a complete dwelling. Any comments? I am considering digging the holes as suggested but I also think I want to pour concrete into cardboard tubes for extra support. But I have a tendency to over-engineer and I wonder if the extra effort is needed.
TIA for your interest in our project.
Jerry
Unless Al Gore is actually right, I'm guessing it is still cold in the winter and there are still frost issues at 9,000' - at least for a few more years anyway. I'd suggest Sonotubes or stacked blocks anchored to footings below the frost line. Your building might not be very large, but at that elevation you are going to have to insulate and finish it out to get year-round use. Depending on the type of interior finish you use, it is possible to get away with gravel and blocks, but windows, doors, and siding can get out of whack if there is even minor frost heave.
I echo the concerns about frost and heaving. We're at 8800 feet in NM. Definite winter with snow and frozen ground. The cabin, with piers at 42 inches depth is rock stable, no problems at all with frost heaving. Our shed sits on the surface more or less. It shifts very slightly. The door sticks a bit. The door is not a conventional door like a cabin or house. It is built more like a sturdy garden or fence gate and has a diagonal corner strap with turnbuckle. It requires a slight twist L in spring and R in when winter sets in solid. Not a big deal for a shed, but it would be a PITA for a living space.
Then there is the wind uplift issue. Higher elevations sometimes have some pretty good gusts. You should have the structure securely connected to the ground. Blocks/pads sitting on gravel offer little uplift resistance. By uplift I also mean forces that while pushing on a sidewall, lifts that side while pressing down on the lee side. That can overload the bearing capacity of piers or footing as well as beams.
If you go with sonotubes keep in mind that the larger the diameter the better. Larger diameter tubes offer greater resistance to sideways movement. High winds can exert a horizontal force that will try to make a pier rotate. The taller the pier the more the rotational force.
Thanks for the replies, participants. I'm going to spend some time looking around this site, and I'll post some photos of our digs in a week or two.