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I just tore off the old decking from my cabin's deck. The joists are set 24" on center as opposed to the 16" on center that were in the specs. Should I take all the joists out and replace all of them, or add a new joist between each existing joist? The deck is about 12 years old and some of the joists have to be replaced due to rot.

  • Hello, and welcome to Home Improvement. You should not be getting joist rotting after 12 years. To avoid it in the future, you should probably put tar paper over each joist to protect it. (Replacing floorboards is much easier than replacing joists.) – Daniel Griscom May 15 at 16:04
  • What "specs"? If you're adding a particular decking product, please revise to say so. Two-by decking can span 24", as can some synthetic decking. The question is unanswerable as it is. – isherwood May 15 at 20:06
  • The decking that was original was 5/4 pressure treated. That is why the 16" o.c. was speced out. I am planning on 5/4 Trex material – JLawler May 15 at 20:35
  • Are you asking whether you should, or how? – isherwood May 15 at 20:36
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The wider spacing is less rigid, you may feel a little flex as you walk. I do not like the flex so I used 16" centers. Also , if you use 2 X decking instead of the recommended 5/4"decking, it will be more rigid and last longer. My 2X decking is 20+ years old in good shape in a warm ,wet location; I have replaced about 5% because of rot ( under planters).

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We design from the top down and build from the bottom up.

So, depending on what type decking you use, you can the decide what size and spacing of joists to use.

For 5/4 material I’d use a 16” spacing. For 2x material (1 1/2” thick) I’d use 24” spacing for plastic decking boards and 36” spacing for Cedar, Redwood and pressure treated boards.

The size of the joists will be determined by the span of the joists. We’d need more info to determine that...

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as opposed to the 16" on center that were in the specs" ??

Someone did not follow specs ??

Since you have to replace some of the joists then you might as well take them all out and do it right this time with treated joists. ( 16" OC, unless you want 12" OC)

If you take them all out to start over then that gives you a chance to inspect the quality of all the other components to make sure any problems are addressed.

NOTE: The word “right” in the phrase “do it right” is referring to Alaska Man’s opinion of what right is for deck joist spacing.

No other participants were harmed in anyway in the formation of this opinion.

  • There's nothing wrong with 24" centers if appropriate decking is used. 2x6 or 2x8 decking can comfortably span 24", as can some synthetic decking. You maybe know this, but it doesn't seem like you consider it "right" from your answer. – isherwood May 15 at 20:35
  • @isherwood I wouldn’t build it 24 on center, thus my answer. The OP specified that there were specs for 16 on center so I was assuming that 16 on center was specified to be the right way. – Alaska Man May 15 at 21:55
  • Fair enough. Folks come to this site with a lot of assumptions about what's correct and what's not. Often they're mistaken. I take your point, though. – isherwood May 16 at 12:42

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