1. Tree Suitability Check
Enter trunk diameter (DBH, measured 4.5 ft off the ground) for each tree.
2. Platform Size
How big should the deck be for the kids who will use it?
3. Railing Check
Guard height and baluster count per IRC residential rules.
4. Ladder Geometry
Ladder length, base distance, and rung count at a safe 75° angle.
5. Load Capacity
How much weight can the deck safely hold? (40 psf live + 10 psf dead)
6. TAB Anchor Sizing
Pick the right treehouse attachment bolt (TAB) diameter for your load.
7. Joist Span
Maximum platform joist span per AWC DCA6 (Southern Pine #2, 16 in o.c.).
Frequently Asked Questions
What size tree do I need for a treehouse?
For a single-tree treehouse, use a healthy hardwood with at least 12 inches of trunk diameter (DBH, measured 4.5 ft off the ground). For two trees, each trunk should be at least 10 inches; for three or more trees, at least 8 inches each. Avoid diseased, leaning, or shallow-rooted trees.
How big should a treehouse platform be?
A common planning rule of thumb is about 25 square feet of deck per child. For example, 4 kids need roughly 100 sq ft, which is a 10 ft x 10 ft platform. Keep the platform as close to the trunk as possible and leave a 2-inch gap around the trunk so the tree can grow.
How high should treehouse railings be?
Residential guards must be at least 36 inches high (IRC R312.1.2) and are required wherever the walking surface is more than 30 inches above grade (IRC R312.1.1). Baluster openings must not pass a 4-inch sphere (IRC R312.1.3), so space balusters no more than 4 inches apart.
What is the best angle for a treehouse ladder?
Set a fixed treehouse ladder at about 75 degrees from horizontal — the standard safe ladder angle (roughly a 1-to-4 base-to-height ratio). Space rungs 10 to 12 inches apart, and brace the ladder base so it cannot slip.
How much weight can a treehouse deck hold?
Design residential treehouse decks for 40 psf live load plus 10 psf dead load, the same as a house deck (IRC/DCA6). An 8 ft x 8 ft deck (64 sq ft) therefore supports 2,560 lb of total live load. Subtract the deck's own weight and divide by 200 lb per person to estimate safe occupancy.
What size TAB (treehouse attachment bolt) do I need?
Typical working loads in healthy hardwood are: 1-inch TAB about 1,200 lb, 1.25-inch about 2,000 lb, 1.5-inch about 3,000 lb, and a 3-inch Garnier limb about 9,000 lb. Divide your total platform weight by the number of TABs and pick the smallest size rated above that load. Always confirm ratings with your hardware supplier.
What size joists should I use for a treehouse platform?
Following AWC DCA6 Table 2 (2015 IRC) for Southern Pine #2 joists at 16 inches on center with 40 psf live and 10 psf dead load: a 2x8 spans up to 11 ft 10 in, a 2x10 spans up to 14 ft 0 in, and a 2x12 spans up to 16 ft 6 in. These are maximums — shorter spans are stiffer and safer.
How high off the ground should a treehouse be?
There is no universal code maximum for a backyard treehouse, but most are built 6 to 10 ft up — high enough to feel like a treehouse, low enough for a safe 75-degree ladder. Once the platform is more than 30 inches above grade you need 36-inch guards, and you should keep at least 6 ft 8 in of clearance if people walk underneath.