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I decided to resurface my existing deck and because there is a fair bit of rot on the joists. When I tore it down to the frame, I noticed that some of the joists are sistered because the deck is over 16' long and I don't think they were able to get lumber longer than 16'.

  • I've seen decks tutorials in the past break a larger deck up into multiple sections using a rim joist in the middle (not sure if it's still called a rim joist if it's in the middle -- happy to be educated here). Is that the right approach here? (Top diagram in the attached image)
  • Is sistering the joist a valid approach, is it better or worse? (Bottom diagram in the attached image)
  • Are there other approaches you would recommend?

A couple of details that are probably relevant:

  • Planning on replacing with composite using hidden fasteners, so I don't think alignment of the joists between the left/right half need to be identical.
  • There are 4 beams supporting the frame, approximately every ~3.5'

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enter image description here

Any and all advice is appreciated!

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  • If it were me, I'd go with the top option, with the joists all sitting in joist hangers and the middle red span also hung properly from the rim joists. I'd probably consider doubling that middle joist and even adding a post. However, I'm neither a framing nor code expert, this is just my gut reaction.
    – FreeMan
    Apr 22 at 11:41
  • Where are your beams here?
    – Huesmann
    Apr 22 at 13:39
  • realize that by sistering the joists, you're buying more wood. And with the center cross joist you are also strengthening the side forces. Which in the second case you'd would do via blocking.
    – DaveM
    Apr 22 at 14:14

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When I did my deck, I pretty much followed your top drawing. The shorter joists were much easier to handle. I doubled up the middle joist and put in two deck posts to support it. I had my joist hangers back to back so the joists were straight.

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  • Thanks, that helps. I'm not replacing the posts/beams, so I'll have to see if I can place that bisecting rim joist over an existing beam if I go down this route.
    – Gophermofur
    Apr 22 at 12:31

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