So I dug my footing holes this weekend as follows:
Po----<8'----Po----<8'-----Po
/ / /
/ / /
<8' <8' <8'
/ / /
/ / /
Pc----<8'----Pc----<8'-----Pc
/ / /
/ / /
<8' <8' <8'
/ / /
/ / /
Po----<8'----Po----<8'-----Po
Po = the row that will support the roof weight (end of pitch)
Pc = the center row of the building (Pc on outside are gable ends)
For all Po holes, I was able to get about 4 feet depth for my sonotube posts - down to some seriously compacted gravel/stone/clay. However, for the Pc holes, I could only dig to about 2 feet.
Thanks to good advice from MOUNTAINDON, it seems that with a box of 2x12 girders at 3 pieces thick, I really dont need the holes labled Pc for footings where I plan to use 16 foot 2x10 floor joists. However, I still would like a girder up the middle along the line of Pc footings - I like the idea of a really SOLID floor - as I stomp around all 230lbs and friends

LOL
I plan to insulate all my footings using the Frost Protected Foundation Guidlines that I found on this site. I'm thinking top layer of 12" loam, 3" gravel, 3" high density foam, 3" gravel, then regular clay soil under - all under the building and going out 4 feet to each side - thus a 20' x 20' insulated area.
If I do this insulation, here is my idea for the footings/piers. For the load bearing Po holes, 5 foot sonotube posts with the "big foot" at the bottom. For the Pc holes, how about just gravel compaceted base, with 4 12" x 16" cement blocks, stacked 2 high, and cemented together, with PT posts on top. I'm figureing that if I use all that insulation, and the Pc footings are not "needed" then I don't need to do deep posts on the Pc row?
My only concern is what would happen if there was heaving of any of the Pc row shallow footings? if that hapens, would the floor in the middle of the building heave? I'm thinking no, but what do you think?
Best thanks for any opinions!
(property is in Northern Maine)