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I am finishing a wraparound porch. I’ve decided to use beadboard plywood panels instead of vinyl, aluminum, or wood tongue and groove planks on the ceiling. I understand why planks would need to run perpendicular to the ceiling joists, but with the boards and my measurements I think it would be simpler for the boards to be installed lengthwise with the joists. Doing that would make the lines in the ceiling run opposite of the deck. Is this just a personal preference? Or some other reason I am not thinking of?

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  • I edited the question slightly to be more clear that I’m talking about the direction of the ceiling boards.
    – Drai
    Aug 2 at 0:44
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To answer your specific question, ceilings usually follow decking because that's the way we've always done it.

I kid: decking usually runs wide (fewer cuts, tradition), and ceiling boards usually run wide because the underlying framing is usually perpendicular to the house. I think we've come to expect this symmetry.

In your case, the strength of the sheet goods (long axis versus short axis) isn't relevant, as it's just holding itself up. So do whatever you want. It might look really cool and it might look odd to anyone that notices. (I sincerely doubt that many people would actually notice...)

This is just my opinion, but the one tiny detail I'd do is to mirror whatever the treatment is in the corners. If your decking is mitered, then miter the ceiling, etc.

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    Thanks @Aloysius that is what I was looking for, to determine if there was more than just an aesthetic reason.
    – Drai
    Aug 2 at 0:47
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Lumber has more strength in the direction of the grain than perpendicular to it. Therefore boards are installed so that they span from joist to joist in the direction of the grain.

Whether a floor board has a dominant strength axis depends entirely on its composition. And whether this matters to you depends on your load calculations and the joist spacing. Check the specs and installation guide for your particular bead board.

Some boards, like OSB, have a major and a minor strength axis. This provides more strength in one direction, which is economically exploited when laying over joists.

For instance, in OSB the strands in the outer layers are aligned parallel to the board's major strength axis, and strands in the inner layers are aligned perpendicular to the major strength axis. The perpendicular axis is also called the minor axis.

With plywood there is an odd number of layers, and adjacent layers have perpendicular grains. There will be one more layer with grains in the direction of the major axis.

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