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I am currently in the process of designing/building a play structure for my son. The structure will include a 5' high elevated deck, that is 6'x4'. The supports for the decking will be 24" center-to-center.

Reading through load tables, it is recommended to use 2x4 or 2x6 stock as the decking, if one is spanning 24". To use 5/4" decking, requires 16" or smaller spans.

The plan for this play structure is, it is for kids, with the occasional "mom or dad wants to play too!" So, in this case, would using 5/4" decking be appropriate? The 2x6 decking seems to be a bit overkill for a kids play set, and the trap-door/ladder I am planning to incorporate would get quite heavy for little guys to manipulate.

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When we were little and were building those kinds of things, we just used whatever lumber we could get our hands on. Of course we didn't have a clue about loads and such. As long as it looked like it would hold, it was good enough. The point is - I would just follow common sense... – Vitaliy Jul 17 '12 at 15:51
Is it possible to reduce the span? – Tester101 Jul 17 '12 at 16:02
@Vitality - Of course common sense goes a long ways, and is what I am trying to do here- common sense with the pocket book. Cedar, unfortunately, is not the cheapest material in the world. I'd prefer not to go get a bunch of 5/4 decking, just to find it deflects too much, and need to spend more/make another trip to the lumber yard ;) – MarkD Jul 17 '12 at 16:48
@Tester101 - Not easily, due to the nature of the design (I am hanging the deck on a 4x4 mortise and tenon frame, with columns spaced at 24". Adding cross members at the beam center points would be possible, but would double the number of mortise and tenon joints I'd need to make.). – MarkD Jul 17 '12 at 16:51

Before writing anything else, let me warn you that I'm not a structural engineer, and I don't claim any competence in these matters. I'm just some random guy on the Internet.

Because I couldn't find a good load table (at least not quickly), I tried to calculate deflection and bending stress, and I can't see anything wrong with using 5/4" x 6" cedar boards (actual dimensions 1" x 5.5") across a 24-inch span:

Decking load calculations

Perhaps I did something wrong in my calculations? Do you have a load table that you trust?

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The ironic thing is- I am a structural engineer by education.. But like you couldn't find any good loading information for Cedar. One minor change (and I'll update my question above), I'll be using western red cedar, which doesn't have quite the strength of white cedar IIRC. I was getting my loading info from here: cedar-deck.org/building-and-finishing/construction/… , which indicates that a 5/4 x 6 would require less than 16" spans. – MarkD Jul 17 '12 at 16:45
Another source for red cedar data—ala‌​s, only valid for 2" nominal thickness and higher. – Vebjorn Ljosa Jul 17 '12 at 17:29

It is not officially recommended, and any chart you will find will list 16" as max span (I've even seen a couple that said 12").

As far as safety goes, it would feel a little "bouncy" to an adult but I'd like to sit back with a beer and watch you try to break it.

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