I have 4x4 posts in concrete for my front yard fence. They are spaced 48" on center. Can I use composite deck boards for the horizontal boards instead of cedar? Or is that too long of a span? Will they will be too floppy? Or too heavy? The fence is only 40.5" high.

  • horizontal rails implying you have vertical boards in between the rails? Nov 16, 2021 at 0:25
  • Maybe I used the wrong word. I will have horizontal boards attached to vertical posts. That is all.
    – Dbloom
    Nov 16, 2021 at 0:30
  • Most commonly the fence boards aren't going to give you as much trouble as the posts, so the advantages (and possibly added expense) of using composite boards for the fencing is pretty much cancelled out by wooden 4x4s...Unless you already have the composite decking waiting around for something to do...
    – gnicko
    Nov 16, 2021 at 2:19

1 Answer 1


The most common boards are 5.25" wide and 1" thick - is that the board you are envisioning? A lot of them have the groove in the middle to accept clips, there are non grooved boards, would you plan for a non grooved board as the top board?

I am going to say yes you'd probably be fine. Decks use them 12" oc but they support the weight of someone walking, fence boards really just have to resist wind loading and the weight of the board above which at 40.5" isn't too crazy. If you do get too much deflection at the mid point you could put a standard horizontal pt rail at the bottom and maybe match it up at the top to hide the grooved side of the top board.

Some composite manufacturers have boards are that 25% hollow and those will weight less and be less likely to have deflection issues. If you have a solid 1" composite board then you'll be more likely to have issues. How will you fasten then between the two posts?

  • I'd be concerned with the 45" or so unsupported width these pieces would be spanning. Composite deck boards tend to be a lot less rigid than similarly-sized wood deck boards, so I'd be concerned that they would sag in the middle in short order.
    – Milwrdfan
    Dec 16, 2021 at 19:05

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