Tree House Dimensions: Platform Size, Height, Posts and Railings
Planning numbers for a backyard tree house: platform sizes in feet and meters, how high to build, railing and ladder dimensions, what size posts and footings to use, and the loads it has to carry.
A typical tree house platform is 6 × 6 ft to 10 × 10 ft (1.8 × 1.8 m to 3 × 3 m), with 8 × 8 ft (2.4 × 2.4 m) the most common size. Children's tree houses usually sit 6 to 8 ft (1.8 to 2.4 m) off the ground. Any platform more than 30 in (76 cm) up needs a guard rail, built at least 36 in (91 cm) high with gaps under 4 in (10 cm).
- Common platform
- 8 × 8 ft (2.4 × 2.4 m)
- Kids' height
- 6-8 ft (1.8-2.4 m)
- Railing height
- 36 in (91 cm) min
- Design load
- 40 psf live + 10 dead
On this page
Tree house platform sizes
The platform decides almost everything else: how many trees or posts carry it, how much lumber you buy, and whether it needs a permit. Sizes that are multiples of 4 ft use whole sheets of plywood and standard 8, 10 and 12 ft joists.
| Platform | Metric | Area | Typical support | Room for |
|---|---|---|---|---|
| 6 × 6 ft | 1.83 × 1.83 m | 36 sq ft 3.3 m² | One large tree, or tree plus 2 posts | Open lookout for 2 to 3 children |
| 8 × 8 ft | 2.44 × 2.44 m | 64 sq ft 5.9 m² | One tree plus 2 posts, or 2 trees | 6 × 6 ft hut, or open deck for 4 children |
| 8 × 10 ft | 2.44 × 3.05 m | 80 sq ft 7.4 m² | 2 trees, or tree plus posts | Hut plus a 2 ft porch |
| 10 × 10 ft | 3.05 × 3.05 m | 100 sq ft 9.3 m² | 2 to 4 trees, or 4 posts | 8 × 8 ft hut with a wraparound deck |
| 12 × 12 ft | 3.66 × 3.66 m | 144 sq ft 13.4 m² | 3 to 4 trees, or 4 to 6 posts | Small room with sleeping space for adults |
A hut on a platform is usually 2 ft smaller than the platform in each direction, which leaves a 1 ft ledge or a deck on one side. For a children's tree house, 8 × 8 ft gives enough room without needing more than one big tree.
How high to build a tree house
| Floor height | Metric | Notes |
|---|---|---|
| Under 30 in | Under 76 cm | No guard required by the IRC; good for toddlers |
| 4 to 8 ft | 1.2 to 2.4 m | Usual range for children; guard rail required; CPSC home surfacing guidance covers falls up to 8 ft |
| 8 to 12 ft | 2.4 to 3.7 m | Older children and adults; stairs safer than a ladder; surfacing must be rated for the height |
| Over 12 ft | Over 3.7 m | Adult builds; posts and bracing need engineering |
Height is limited more by the tree than by preference. The platform should sit where the trunk is still thick and where branches leave a clear rectangle. Lower is easier to build, inspect and supervise. For children, 6 to 8 ft feels high and keeps falls within the range that mulch or wood chips can cushion.
Treat the area under and around a children's tree house like playground equipment. The CPSC home handbook calls for at least 9 in (23 cm) of wood mulch, chips or shredded rubber, installed 12 in deep, extending 6 ft (1.8 m) beyond the platform, for fall heights up to 8 ft.
Railing, ladder and stair dimensions
A tree house is a small building and a piece of play equipment at once. Building to the stricter of the two sets of numbers is the safe choice.
| Element | Dimension | Source of the figure |
|---|---|---|
| Guard (railing) height | At least 36 in 91 cm above the floor | IRC R312, residential guards |
| Gaps in the guard | A 4 in 10 cm sphere must not pass | IRC R312 |
| Gaps for young children | Under 3.5 in 9 cm, no climbable rails | CPSC home playground handbook |
| Ladder rung spacing | 10 to 14 in 25-36 cm, uniform | OSHA 1910.23 (fixed ladders) |
| Ladder width | At least 16 in 41 cm between rails | OSHA 1910.23 |
| Stair riser | 7.75 in max 19.7 cm | IRC R311.7 |
| Stair tread | 10 in min 25.4 cm | IRC R311.7 |
Use vertical balusters rather than horizontal rails, which children climb like a ladder. Put the ladder or stairs where a child stepping off the top lands on the platform, not on a gap, and add a gate or a turn at the top of the opening.
Tree size and how to attach the platform
- Trunk size: a common builders' rule is a trunk at least 12 in (30 cm) thick at the attachment point for a platform carried by one tree. Smaller trees should share the load with posts.
- Species: mature hardwoods such as oak, maple and beech are preferred. Check for rot, cracks, fungus at the base and dead limbs before you build, or have an arborist look at it.
- Attachment: one large bolt does less harm to a tree than many small ones. Purpose-made treehouse attachment bolts (TABs) of about 1 to 1¼ in diameter carry a beam on a short steel arm. Avoid wrapping cables or boards around the trunk, which girdle it.
- Growth and sway: leave a gap of a couple of inches where decking passes the trunk, and use sliding or floating brackets when a platform spans two trees, so the trees can move independently in the wind.
Post size: 4×4 or 6×6
A nominal 4 × 4 post is actually 3½ × 3½ in (89 × 89 mm); a 6 × 6 is 5½ × 5½ in (140 × 140 mm), with more than twice the cross-section. The 2015 International Residential Code deck table limited 4 × 4 posts to 8 ft and allowed 6 × 6 posts up to 14 ft. Later editions set limits by species and the area each post supports, but the practical answer is unchanged:
- 4 × 4: short posts (under about 6 to 8 ft) on a small, low platform, with the beam sitting on top of the post.
- 6 × 6: taller posts, posts with a beam notched into the side, posts with knee braces bolted on, and any platform where adults will stand. This is what most inspectors expect.
Brace free-standing posts diagonally to the platform. A platform on posts alone behaves like a raised deck, and the deck dimensions guide covers joist spans and beam sizes. Actual dimensions of all common boards are in the lumber sizes chart.
Loads and footing size
The IRC designs residential decks for a live load of 40 lb per sq ft (psf) plus about 10 psf for the structure itself, 50 psf in total. The same figure is a sensible minimum for a tree house, since a group of children jumping counts as a live load.
| Platform | Total load | Posts | Load per post | Footing needed |
|---|---|---|---|---|
| 6 × 6 ft | 1,800 lb 816 kg | 4 | 450 lb | 0.3 sq ft (8 in round); use 12 in |
| 8 × 8 ft | 3,200 lb 1,451 kg | 4 | 800 lb | 0.53 sq ft (10 in round); use 12 in |
| 10 × 10 ft | 5,000 lb 2,268 kg | 4 | 1,250 lb | 0.83 sq ft (12.4 in round); use 14 in |
| 12 × 12 ft | 7,200 lb 3,266 kg | 6 | 1,200 lb | 0.8 sq ft (12.1 in round); use 14 in |
The table assumes posts carry the whole platform and that the soil bears 1,500 psf, the lowest presumptive value in the IRC. A platform supported partly by a tree puts less on each post. The bottom of each footing must sit below the local frost depth, which your building department sets: around 12 in in the warm South, 32 to 42 in across much of Ohio, and 48 in or more in the northern states.
Permits and neighbors
Tree houses fall between categories in most codes. Under the International Residential Code, a one-story detached accessory structure of up to 200 sq ft is exempt from a building permit, which covers most children's tree houses if the town applies it. Many towns use 120 sq ft instead, and zoning height limits and setbacks from property lines still apply; a tree house that overlooks a neighbor's yard is the usual cause of complaints. For ground-level alternatives, see playhouse sizes, and plan around other equipment with the swing set clearance guide.
Frequently asked questions
Can I build a treehouse on 4x4 posts or do they need to be 6x6?
4 × 4 posts (actual 3.5 × 3.5 in) can work for short, lightly loaded posts; the 2015 IRC deck table allowed them up to 8 ft tall. Use 6 × 6 posts (5.5 × 5.5 in) for anything taller, for posts carrying a beam notched into them, or where knee braces attach. The 2015 table allowed 6 × 6 up to 14 ft, and many inspectors expect 6 × 6 for raised platforms.
How big should the footings be for a tree house?
Size them from the load. An 8 × 8 ft platform at 50 psf carries 3,200 lb; on four posts that is 800 lb each, which needs about 0.53 sq ft of footing on 1,500 psf soil, a 10 in round footing. Use at least 12 in diameter, and set the bottom below your local frost depth, which in much of Ohio is 32 to 42 in.
What are the dimensions of a treehouse in metres?
Common platforms are 1.8 × 1.8 m (6 × 6 ft), 2.4 × 2.4 m (8 × 8 ft), 3 × 3 m (10 × 10 ft) and 3.7 × 3.7 m (12 × 12 ft). A typical children's tree house floor sits 1.8 to 2.4 m up, with a 0.9 to 1.1 m railing.
Is there a standard size for a tree house?
There is no single standard, but 8 × 8 ft (64 sq ft, 5.9 m²) is the size most plans and kits use. It fits on one healthy tree with support posts, holds a small hut of about 6 × 6 ft with a deck, and uses whole 8 ft lumber and 4 × 8 ft sheets.
Does a tree house need a permit?
Often not, if it is small. Under the International Residential Code, a one-story detached accessory structure up to 200 sq ft is permit-exempt, and some towns apply that to tree houses. Others use 120 sq ft or treat tree houses separately, and height and setback rules still apply, so call the building department.