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Richo 06-27-2011 07:48 PM

Help with deck footings
Going to be building an attached 16 X 16 deck soon. I already spoke with the building inspector about footings and he gave me some calculations on the size and spacing of the footings but I'm in need of help with one calculation.

Apparently I will need footings at the base of the stairway but I don't know how to calculate the location of them, or how high to pour they so that they match up with the bottom of the stringer. The deck is going to be between 5 and 6 feet from the ground at the location of the staircase but I'm not exactly sure because the landscaping is not done yet and the final grade has not been determined.

It would be easiest to just pour those footings after the deck is built when I can line up the stair stringer to the ground, but that would mean renting a power auger twice and I'm trying to be as cost effective as possible.

I thought about pouring them low and then using short posts to attach the stringer to the footing, but then we're talking about direct soil contact to the wood which someday is going to result in rot.

Any advice on how to figure this out?

Also, what is the advantage of using cardboard form tubes vs just pouring the concrete into the hole?


Daniel Holzman 06-27-2011 08:42 PM

When I did my deck, and did my design using a CAD program I have. I carefully measured existing elevations, and fixed the elevations of all the beams. The footings were no problem, because I used 6x6 posts attached to the footings using galvanized brackets (I used the Simpson model, but there are other companies that make similar brackets). I cut the posts at the correct elevation after they were installed using a handsaw.

If you plan to use short posts to support the bottom of the deck stringer, you can do something similar, assuming your building inspector approves. The wood posts are supported on brackets, so there is never any contact between the PT posts and soil.

As for using sonotubes (cardboard forms) versus just placing the concrete in the hole, you can do either, but you save a little concrete with the sonotube, and you prevent the hole from collapsing and getting soil into the concrete, which weakens the concrete. You also get a neat appearance for the part of the concrete footing which sticks up above grade, which in my case was about 6 - 12 inches.

12penny 06-28-2011 06:39 AM

Page 19. Gives you a little room for error. Use ground contact posts.

I think this method works best, especially if the posts holding up your stringers will also be used for guard rail. Seems more solid to me.

Richo 06-28-2011 09:08 AM

So are you saying to have the hand rail post at the bottom of the staircase attach to the footing? That would make sense but we're going with composite material, so is that going to be sufficient for ground contact?

Thanks for the info.

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