I'm planning a new deck (completely replacing and enlarging an existing deck). The deck will be 25'x15' w/25 ft being attached to the house. I'm trying to determine what footings are required.
Local code requires going down 48" and the soil is rather sandy (I'm assuming 2000psf capacity). There will be a 1' cantilever on all sides. Height is low, between 20" and 32" depending on side. I'm planning on 2x8 framing with double 2x8 beams and notched 6x6 posts with joists running on top of the beams. Posts would be anchored on top of the footings, not embedded. Due to a potential snow load, I'm aiming for 80lb load.
Deck planning software tells me do two rows of 6 footings, one at 7 ft and another at 14 ft from the ledger. 6 footings would put them at 4'7" apart. I would like to use 10" sonotubes to reduce the amount of concrete,but using the calculator at http://www.ideasfordeckdesigns.com/calculators/deck-load-calculator.php with that setup gives me a minimum size of 13".
So this question is two parts.
1) Can a 6x6 post sit on a 10" round footing in general?
2) How would using the BigFoot system impact the footing capacity? Since it's 25" wide at the base, does that significantly increase the capacity of the footing? I'm unsure of how it impacts the calculations, I assume it increases the amount of load the footing could take, but couldn't find a reference that said that in a language I understood...
Bigfoot-style post base: