I have an old deck with 16" joist spacing but that was because they used 2x8 joists and span 9 ft with 3 ft overhang.

I am planning to extend the deck but won't go further than 9 ft. So with short joist span, I am thinking using Hem-fir 2x8 with 24" spacing according to this


Do you think it's reasonable? Or do I have to follow the same pattern of joist spacing when I extend the deck? The beam is 4x8x16.

  • Regardless of load-bearing aspects, I find joists on 24" spacing results in too much sag of the decking that is put over them. Commented May 19, 2016 at 1:42
  • I am planning to use composite deck so I am not sure if that is any different. But if you have experienced the sagging issue, it's probably true.
    – HP.
    Commented May 19, 2016 at 2:55
  • 3
    @HP - It is my experience that composite decking is even more flexible than regular wood decking of similar thickness. In one case I was on a deck where it was built of composite material with uniform joist spacing. However part of the decking was installed at right angles to the joists and part was installed at 45 degree angle to the joists. The angled portion of the composite deck planking was noticeably more flexible and bouncy than the right angle portion.
    – Michael Karas
    Commented May 19, 2016 at 3:15
  • I agree composite really needs the tighter spacing. It will sag and feel really spongy at 24".
    – Ed Beal
    Commented May 19, 2016 at 13:13

1 Answer 1


As requested, composite really needs the tighter spacing. It will sag and feel really spongy at 24".

  • While I'm inclined to agree, some supporting material to bolster this would be useful to add power to the answer. Commented Jun 3, 2016 at 14:52

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