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I'm trying to rebuild our deck. How do I attach a 2X8 board to a 8 inch block concrete wall? What size concrete screw do I need?

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  • are you screwing in the block or true the block
    – Traveler
    Commented May 21 at 22:16
  • What do you mean when you say "rebuild?" Are you replacing a board that's already screwed to the block wall?
    – Huesmann
    Commented May 22 at 11:46
  • I've revised your title since your assumption that screws are the right method is faulty.
    – isherwood
    Commented May 22 at 14:43
  • Do you have access to the interior of the wall?
    – isherwood
    Commented May 22 at 14:50

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Many jurisdictions have outlawed screw attachment for ledgers and beams, be it into a wooden rim joist or into concrete block. My experience tells me that screws (such as Tapcons) are woefully inadequate for this purpose. I might trust sleeve anchors into poured concrete, but not ungrouted block. There's too much potential for blowout due to tension.

I suggest through-bolts with substantial backing plates. 3" x 3" in 1/4" steel would be appropriate. You'd want to put the bolts through adjacent to a block rib so you aren't risking collapse upon tightening.

You may also find purpose-built hardware from the likes of Simpson Strong-Tie, but a quick search didn't turn up anything for this case.

Your best course of action is to contact your local inspection office (or one in a nearby community if you're way rural) and ask what they're looking for, regardless of whether you intend to file a permit. At least you know you'll be in compliance.

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