Joist Spacing Depending on Deck Board Dimensions

I have a 10x16 foot deck that I'm about to replace the decking and railings on.

The deck was built before I bought the house and they used 16 foot 2x6's for the joists with a spacing of 22in. I want to replace the decking with composite decking and I read that you need a min of 16" spacing.

Since I plan on adding a joist in-between the current ones giving me 11-inch spacing, could I use a 2x4 or should I stick with 2x6? I'm in the mid-Atlantic region if that makes a difference. I rather do all the work myself so I can better my carpentry skills but this issue stumps me.

Editor Comments
I would stick to those recommended maximum spans of 16 inches. However, you should verify with the local code official, if you've got a code official, that's going to be coming around and checking up on what you're building.

And I would not use a 2x4 as a joist in between the existing 22" joist bays. That is just too small and not structurally sound.

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Video Recap


Hey, just got another email from one of our visitors from the Mid-Atlantic part of the country and he says:

"I have a 10 by 16-foot deck that I'm about to replace the decking and the railings on. The deck was built before I bought the house and they used 16-foot 2 by 6's for the joists with a spacing of 22 inches. I want to replace the decking with composite decking and I read that you need a minimum of 16 inches of spacing. Since I plan on adding a joist in between the current ones, giving me a spacing of 11 inches, could I use a 2 by 4 or should I stick with 2 by 6?"

I think he's referring to the type of deck boards and, you know, with composite boards, you never see them spanning more than 16 inches and sometimes, and if you're putting them on a 45-degree angle, they recommend that you bring the joist into 12 inches.

With that kind of a synthetic material, I would definitely stick to those recommended maximum spans of 16 inches. However, when you bring the joists into 11 inches as we see here, and I'm using 2 by 4's to simulate 2 by 6's, so just assume those are 2 by 6's. If we were to take a 2 by 4 and place this on the framing like that, I can tell you from my years of experience that this is going to be more than sufficiently strong.

However, I caution you, I would say that you probably shouldn't just take my word for it as the gospel. You should verify with the local code official, if you've got a code official, that's going to be coming around and checking up on what you're building.

But I would be shocked if there is a contradiction to what I'm suggesting here because this is just a very robust construction method. The tightness of those joists with the thickness of an inch and a half material and you should be just fine.

Hopefully, that helps you and do check with your local code official to verify that what I'm suggesting would apply in your area.

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