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I'm planning to build a pergola on my existing deck and am looking for advice on how to securely fasten 4x4 posts to the deck. The deck is approximately 2 feet off the ground and is supported by concrete footings. I intend to place the 4x4s directly above these footings. I will be using brackets to hold the 4x4s in place, but I'm unsure about the best method to fasten these brackets to the deck and underlying joists.

Some of the options I'm considering include:

  • Drilling fasteners directly into the deck joists from above.
  • Using blocking between joists for additional support.
  • Using long concrete fasteners to attach the brackets directly to the concrete footings below the deck.

Additional Information:

  • I live in the South, where high winds are a possibility.
  • I haven't fully designed the pergola so can't provide exact details yet
  • Given the exposure to high winds, I'll consider corner braces, maybe a railing for some additional support, etc.
  • I've included below a picture of a concrete footer and the deck beams

Questions:

  1. What is the most secure method for fastening the brackets to the deck and joists?
  2. Are there any specific types of fasteners or brackets that you would recommend for this project?

Related questions: there are a number of related questions that don't quite answer mine. This being Stack Exchange, always good to note, especially in case someone is looking through here someday in the future.

Image of concrete footer and deck beams

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  • 1
    The deck boards will not hold
    – Traveler
    Commented Sep 12, 2023 at 1:10
  • @Ruskes do you mean that I can’t just fasten to the deck boards? If so that’s why I’m asking for advice on connecting to the beam/joist
    – mbarete
    Commented Sep 12, 2023 at 2:28
  • is it 8 foot long ? it would apply to much share pressure to a single deck board, that will snap
    – Traveler
    Commented Sep 12, 2023 at 3:34
  • You'd need to connect through the deck boards to the joists or posts.
    – Huesmann
    Commented Sep 12, 2023 at 13:02
  • 1
    @mbarete if you're able to remove the deck boards in the area where your posts will go, you could add some blocking that you can screw into.
    – Huesmann
    Commented Sep 13, 2023 at 13:19

2 Answers 2

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Attaching to the deck boards isn't a big deal as long as they're aligned with the beam plus foundation below. Use a hot-dip galvanized equivalent or better post base and use hot-dip galvanized fasteners--the screws laying in your image are inappropriate. Simpson brands their hot-dip equivalent or better post bases as ZMAX, where I assume the zee is for "zinc." If someday you need to replace the deck boards but not the pergola, then you might regret not notching the deck boards so that the posts sit directly on the beam.

Your question is actually about preventing sway in the wind. Detailing the post connection to prevent that sway is a waste of time because you've announced that you're fine with railing preventing sway and because your deck is so low. With the low deck, no handrail is required, so you don't need to implement the IRC's finer handrail details. To brace each post against sway, just install an X-brace in the handrail bay beside the post. Wire rope is probably the easiest to detail. Just remember

  • that your rail has to be somewhat substantial. This is because the X brace starting at the post base ends at the rail and uses the rail to push back against the post.
  • Also, the connections between rail posts and deck surface are critical.
  • Also, the connections between X-braces and posts are critical, where any eye bolts should have shoulders.
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  • Amazing thanks for answering a question I had assumed to be dead
    – mbarete
    Commented Nov 10, 2023 at 22:08
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See where you want the posts and remove the boards. You can use concrete footings (if you do put a couple of inches of crush and run under them) or the the metal spike ones. Secure the 4x4s to the footings. You can also screw them to the joists as well. Mark the boards and cut them so the post can go through. Best to place the post between 2 boards so each board so you can split the cut. Re-install the boards.

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