Footing for a porch?

Question

To waterproof the front of our house, we have removed the existing porch and we're debating how to build the new one. The cold room that the old porch was on top of is about 4.5 feet wide, 3.5 feet deep. The cold room is the full height of our basement, about 7.5 feet.

We have received a proposal to build a new porch.

The idea is to tear out the floor, footing and walls removing the cold room entirely. Then we would back fill it, tamp it down, and build a new porch on top.

The design for the this porch calls for 22 in. wide by 9 in. deep footings. We've heard differing opinions that recommend a three foot deep footing.

Is 22 in. x 9 in. sufficient?

The frost line in our area is about three or four feet.

Answer 1

You definitely want your footings to extend below the frost line, otherwise as the ground freezes below your footing it will swell (as water does when it freezes) and the force of the swelling WILL push your footings out of position.

Ice breaks mountains - a porch doesn't stand a chance. :) Dig DEEP. With a frost line going as low as 4', I'd dig down 5.

However, that said, the FOOTING doesn't need to be 22" wide from 5' down all the way to the surface - a 22" by roughtly 12" deep footing put 5 feet down and a 6" or so wide reinforced wall coming up to surface would avoid the problems of freezing and save on concrete while offering structure.

This kind of work usually requires a permit as well, and its hard to conceal, so you might want a structural engineer to draw up proper approve-able plans.