Joist spacing for composite decking

I'm getting ready to redo my existing deck, at least the deck boards and rails. The joists, beams and posts seem to be in good shape (I have access underneath). I'm looking at replacing the deck boards with composite boards because I just don't want to have to deal with the maintenance (particularly staining). The existing joists are 2x6 set 16" OC with a span of 8'. The boards I'm looking at all say that 16" OC is fine, but since this will be in full sun in the southeastern US, I'm worried about sagging/warping. I'd like to make that spacing 12". So this leaves me with a couple of obvious options I can think of: either cut out the existing joists, move them to 12" OC, and add more, or add one additional 2x6 between every existing joist making them 8" OC. The thing that I worry about with both of these options is that any treated 2x6 I buy is likely to not have shrunken, and therefore be larger than the ones that have been there for 15 years. The existing joists were installed with a 2x2 ledger and toe-nailed instead of hangers. So if I take a not-shrunken 2x6 and put it on top of the ledger, it's very likely to sit higher than the existing joists. So this leads me to my question. Could I just add a 2x4 between every existing 2x6 to give that extra strength? Would this even be effective? What if I also block them in the center between the existing joists? Is this viable, or just a terrible idea? I know that by itself, a 2x4 with an 8' span would be unacceptable. But this would be 2x4's and 2x6's set alternating at 8" OC. This would make it so I could set them to the same height as the existing joists, and not have to remove them either. Thank you in advance for your feedback! submitted by /u/Quixlequaxle [link] [comments]

Mar 10, 2025 - 23:04

I'm getting ready to redo my existing deck, at least the deck boards and rails. The joists, beams and posts seem to be in good shape (I have access underneath). I'm looking at replacing the deck boards with composite boards because I just don't want to have to deal with the maintenance (particularly staining).

The existing joists are 2x6 set 16" OC with a span of 8'. The boards I'm looking at all say that 16" OC is fine, but since this will be in full sun in the southeastern US, I'm worried about sagging/warping. I'd like to make that spacing 12". So this leaves me with a couple of obvious options I can think of: either cut out the existing joists, move them to 12" OC, and add more, or add one additional 2x6 between every existing joist making them 8" OC.

The thing that I worry about with both of these options is that any treated 2x6 I buy is likely to not have shrunken, and therefore be larger than the ones that have been there for 15 years. The existing joists were installed with a 2x2 ledger and toe-nailed instead of hangers. So if I take a not-shrunken 2x6 and put it on top of the ledger, it's very likely to sit higher than the existing joists.

So this leads me to my question. Could I just add a 2x4 between every existing 2x6 to give that extra strength? Would this even be effective? What if I also block them in the center between the existing joists? Is this viable, or just a terrible idea? I know that by itself, a 2x4 with an 8' span would be unacceptable. But this would be 2x4's and 2x6's set alternating at 8" OC. This would make it so I could set them to the same height as the existing joists, and not have to remove them either.

Thank you in advance for your feedback!

submitted by /u/Quixlequaxle
[link] [comments]