The required bearing areas of the footings depend on the nature of the soil and the load on each post from the deck. I don’t remember the specifics, but we did the calculations for our deck. What I do remember is that with the snow-load (including what may slide off the roof and/or accumulate from drifting), the design load for the deck was about 300 pounds/square-foot!
Thank you Larry and Allen! I will probably go 24 inches deep because that is what I used to do for a bit more stability with a few pieces of rebar in the footing even though it may not be necessary.
FWIW, If the location of the footings will be exposed to heavy runoff (from roof or sloped lot), consider going deeper than required. I have 3 footings that are over-exposed because of soil loss; I wish they had been set deeper. Next project for when the snow melts. 😉
Hello, I am thinking about a deck extension and will need a few footings. Does anyone know the minimum depth for frost line? Otherwise I would just dig 2 foot by 1 foot for the footing. Thanks!