Simple Playhouse Deck

Lay the 4x4 posts flat and screw the first side boards to them with 3" screws, per the diagram. Building the swing option? One post per side is a 96-footer — decide which end of the playhouse faces the swing before this step, not after.

Attach the remaining side boards to the posts with 3" screws, forming the 8x8 rim. Now the real work: level the frame on the actual ground (dig or shim under posts — dirt moves, framing doesn't) and square it by matching diagonals.

The plan promises it won't be square on the first try, and the plan is right. Take the time; every later piece inherits this geometry.

With the box square AND level — verify both again — screw the eight 45°-mitered braces across the corners. These freeze the geometry: they make a square frame permanent and a crooked one permanent too. That's why they come after the fight, never before.

Mark the joist layout on the long sides — even spacing, roughly 16" centers — and screw each joist through the rim with 3" screws, three per end, tops flush with the rim top. Sight down the tops: a proud joist telegraphs a hump into the deck.

Screw the sixteen deck boards across the joists with 2-1/2" screws, two per crossing, small even gaps for drainage. Start flush at one edge and check remaining spacing every few boards so the last one isn't a sliver.

Sand the whole surface and every arris — this deck hosts bare feet, crawling knees, and eventually someone's sleeping bag.

Screw the 2x4 cross braces under the deck per the diagram, into the framing — they stop side-to-side sway once kids discover the deck is also a stage, a ship, and a trampoline.

Paint or stain everything, then build whatever the platform was for: walls, railings, the swing arm. The hard part — flat, level, solid — is done.