We have an old 25x25' cabin in Northern California that's rotted its footings a bit. It was originally set on piers with pads of various types, including cedar rounds which I can now dig out with a shovel. After almost 100 years the supports on both uphill and downhill (3-4' of drop) sides have rotted to the point that the floor bows several inches (the middle supports stayed dry). The doors now jam against the floor, and we did some minor jacking to get a sliding door square.
The cabin is of fairly lightweight construction, with a corrugated roof, 48" OC studs (!) standing directly on the subfloor (no bottom plate), and minimal finish materials. The floor is 2x6 joists at 16"OC, sitting directly on shims on the uphill side (redwood and cedar throughout). From looking up the lumber weights I guess it's 8-15,000 pounds.
From looking around the web I've found permanent screw jacks which we could probably install for a few hundred dollars, with enough capacity to lift the downhill side and get it onto concrete pads, instead of the buried cedar log it's resting on now. I'd like to put a purlin across the bottom of all the joists (they run uphill/downhill) and jack the whole side level instead of jacking each joist and fitting a pier under it (labor-intensive).
My questions are:
Is there a way to "sanity check" my weight estimate? Is there a ballpark figure I could use for psf?
Is there a safety procedure to follow? If I use screw jacks I'll have to get several feet under the structure and turn the jacks.
Is there a problem putting the purlin, etc., a couple of feet uphill (farther under) from the downhill sill? The aforementioned cedar log is suspect at this point and I'm thinking the pads should be on soil, above the log at least.
Thanks for any perspective people might have to offer.