Deck stair footings

Old 07-06-16, 08:28 PM
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Deck stair footings

I have determined the size of the stair case and number of stringers I will need, but am still wondering about the footings. My stairs will be 8' wide so I will need 6 stringers at 16 OC. Do I need to have footings below the frost line (40 inches for Chicago) for each stringer? What size do they need to be, ex: 10in or 12in wide pier with a 24in footing? Also, what do you recommend to use to attach the stringers to the footings?

Im obviously green to this so any information is helpful.

Thanks in advance
Old 07-06-16, 08:52 PM
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Putting a pier every 16" would be pretty silly... you may as well excavate and pour a footing and stem wall that's 9' long. I don't know if you plan to pour a sidewalk or anything, but if so you could notch the top of the stem wall so that the sidewalk that is under the front riser will be stable. Its pretty hard to determine exactly where those stringers will go at the cement phase, so I would suggest you use something like a Simpson HD3B hold down, which you can drill into the stem wall later after the stringers have been laid out and set.

Another way of doing it would be to anchor a treated 2x4 flat on top of your stem wall, then notch the front of your stringers to set on top of the 2x4. The notch prevents them from kicking out and you can toenail to the 2x4.

And 8' wide stairs 16" oc would equal 7 stringers.

I would probably make the stem wall 6" wide, (2" notch for sidewalk to sit on + 4" stem wall for the back of the stringer to sit on), and center the HD3B in the 4" portion. Footing twice as wide as the wall, so 12" wide, 1.5x as thick as the wall is wide, so 9" thick with rebar.

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