Large Covered Sandbox

Dig and rake a level surface for the sandbox first — this is the step people skip and regret. Build the box from the 2x8 sides, fastening the corners with 3" screws; predrill and countersink so the ends don't split. Set it on the pad and level it using rocks as shims or by digging down the high spots.

Fasten the top trim to the two LONGER sides first with 2" screws, keeping inside edges flush. This wide trim is what kids sit on, and it starts tying the box together.

Add the remaining top trim, screwing it so it overlaps the corner joints of the 2x8 sides. Fasten it into BOTH sides at each corner — that overlap is what reinforces the joint against the outward push of a full sandbox.

Stand the four 2x2 canopy posts in the corners. They double as corner blocking, so screw each into both side pieces — two screws per side, eight per corner. This is what makes the corners genuinely strong, not just the trim.

Build the canopy top frame from the 1x4 sides across the tops of the posts, and add the 45°-mitered corner braces to keep it square and straight — check the frame is square before fastening the braces.

Stretch a fabric canopy over the top frame and lay a bottom liner in the box if you want a weed and critter barrier. Sand any splinters where kids sit and reach.