Treehouse and playhouse platform planner

How we work it out

Framing. We size joists, beams and posts with the IRC deck tables (R507.6, R507.5 and R507.4), built for 40 lb per sq ft: far more than a few kids. Joists span the depth between two beams; beams span between posts, and we add posts until a beam fits. A freestanding platform also needs diagonal braces at the posts, which the deck tables don't size.

Railings. CPSC's home handbook wants a guardrail or barrier on any platform over 30 in: at least 25 in high up to 48 in, a barrier at least 27 in up to 72 in, and at least 33 in above that, with gaps under 3 1/2 in. The building code asks 36 in on a deck, so a fort that your town counts as a deck may need the taller rail.

Getting up. CPSC's public playground guide keeps ladder rungs no more than 12 in apart, stair steps to 7 in for toddlers and 9 in for preschoolers, and toddler platforms no higher than 32 in. Over 6 ft, add a landing on the way up.

In a tree. No code table covers a load hung on a moving tree. Treehouse hardware makers use special bolts, one fixed connection with the rest free to slide, trees at least 8 to 12 in across, and joists kept 6 in from the bark. The International Society of Arboriculture says to keep soil compaction off the roots and to have a certified arborist check the tree.