[Richo]

Hello all

I have a 16 X 16 attached deck I'm going to be building. The building inspector gave me a formula to work with to calculate the size of the footings based on the weight of the deck.

The beam will be 14 feet out from the house with 4 footings spaced at 4 feet.

He said the ground is rated for 2000 psf which comes out to about 14 psi.

He calculated that the beam will be supporting 7200 pounds of maximum weight (16 feet of width X 9 feet of depth X 50 pounds per square foot).

This means that each footing is going to have to support 1800 pounds. Based on calculation, it would take 14" diameter footings to carry this load. The power auger I can rent only goes up to 12" diameter.

14" footings or 5 12" footings to me sounds like overkill but I know it all comes down to what the inspector requires. Does that sound right to you?

I'm in WI so the footings have to be poured 48" deep so we're talking about a lot of bags of concrete.

Thanks for your help.

 

[Richo]

I don't doubt his calculations but originally when I talked to him about 3 footings instead of 4 he did some tapping on the calculator and said "You might need to go with 10 or 12 inch footings" so he wasn't clear about it.

Based on the formula he gave me I later did the calculations and concluded that I needed 4, but they come out to 14" to meet the code.

I guess I will have to run it by him and see what he says.

Thanks