I'm putting a little porch off the back of a friend's house. It's going to be free standing with four posts set on footers, etc.

What I need to know is:

What dimension of lumber will suffice for a beam over a 4 foot span?

i.e. the longest the posts will be set apart is 4 feet and I don't want to use a 2x12 if a 2x6 will do.

What is the frost depth in the Washington, D.C. area?

ie. how deep do my footer posts have to be?

What do I set the bottom of the stair stringers on? They are very short, only three steps. Do I need to sink more holes and posts and bolt them in place or can I get away with a small concrete pad set flush with the ground for them to rest on? Can't they just ride on that?

Any help you can give would be most appreciated.

Doug