I'm building a rectangular sandbox under a deck, using 4 of the deck posts as corners. The dimensions are about 9 1/2 feet and 5 1/2 feet to the outside edges of the posts. Originally I was going to use 5/4 deck boards for walls, but now I'm having second thoughts about their strength. Is there a reference for this other than my gut or anyone else's experience? There's about a 6 inch slope along the 9 foot run, if that matters.
To thin and will bow out.
Use 2X's, or better yet 6X 6's.
If you go with 2X's use 6" long Deck screws in the corners to hold it together. Nails will just pull out.
With 6 X 6's or doubled up 4 X 4's notch the ends, drill 1/2 holes and pin the corners with 1/2 X 24" rebar.
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