As the below picture, is the rough blue print of the 12'6" x 12" deck for my new house.

Following the code, all joists(blank rectangular) are 2 x 8 16" OC, the blue rectangular is the beam, and gray rectangular is ledger board which already attached to house by builder. The yellow rectangular is the post for aluminum railing(only draw right side), the railing post size is 4 x 4 inch at the bottom(mount by bolt and blocking board, see figure 2).

Because I want to give more space for the deck and make the railing parallel with the house side wall, I need to make the right joist 2.5" (total 4" gap, 1.5" for board thickness) away the ledger board due to the ledger board is short, the other side of the joist can sit on the beam.

How to frame the right joist to make it strong enough for the railings?

deck frame

railing post mount

railing post mount (figure 2)

1 Answer 1


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Add 2 or 3 blocks perpendicular to the joists directly under the post locations. The longer the block are the better to minimize splitting when you run the post mounting screws into them.

You may already plan to, but you can move the posts over the last joist to get a little more room on your deck.

When the mounting screws go through the decking, sandwiching everything up will be quite strong.

But this does only address the strength of the railing. The joists must attach to the ledger, no "floating" joists

  • My ledger is's longer enough, how to fix that floating joists issue? Short 4".
    – tywtyw2002
    Jun 12, 2017 at 18:04
  • You need to remove at least a 4-foot section of your existing ledger and then replace it with the piece that's long enough to catch the last joist. Or move the last joist in that four inches
    – Jack
    Jun 12, 2017 at 20:56

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