Gates before anything is drilled
This is a concept plan, not an engineered design. TAB capacity figures come from vendor and builder pages, not a stamped calculation. The brace geometry puts side load on the TAB perches, and the beams cantilever about 47" past their supports with only a 25⅜" backspan. Have a certified treehouse builder or a structural engineer review the attachment layout and TAB size before the first hole is drilled.
- Arborist assessment of the oak. Health, decay, cavities, deadwood, root zone, and when bolt wounds are least harmful. A load-bearing tree is the one part of this you cannot replace.
- Permit and zoning check with Roxbury. Connecticut’s permit exemption covers “one-story detached accessory structures used as tool and storage sheds, playhouses and similar uses” up to 200 sq ft, but whether an elevated tree platform counts is the town building official’s call. Zoning setbacks apply separately.
- Insurance. Ask your homeowner’s carrier whether a treehouse is covered and what it requires.
- Call 811 before digging stair footings.
- Site survey. Height of the first branch, trunk diameter at the intended TAB height, grade at the stair foot, and which way the slope falls. These set deck height and stair length.
How the platform hangs on one tree
Four TABs sit around the trunk at 45° angles, about 10" past the bark to the bracket. Each of the two beams rests on two of them, one on each side of the trunk. Joists cross over the beams, so the deck extends about 4 ft past the beams in every direction. A second ring of four TABs, 36" lower, holds the knee braces that run out to the beam ends and take the cantilever. The platform opening leaves about 4" of clearance to the trunk on every side so the tree can grow and move.
Dimensions
| Item | Dimension | Notes |
|---|---|---|
| Trunk | Ø 16" | As stated. Species: oak. Measure again at the actual TAB height. |
| Platform | 120" × 120" (10'-0" × 10'-0") | Outside of framing. 100 sq ft. |
| Deck height | 84" (7'-0") nominal | Top of deck above average grade at the trunk. Site dependent; see grey areas. |
| Beams | 2 × doubled 2×12 × 120" | Parallel, 25⅜" center to center; 3" laminated width; each beam’s inside face is 3¼" from the trunk at its closest. |
| Upper TABs | 4, at 45° around the trunk | Perch ends at 12.7" either side of trunk center; each beam rests on two. Bracket height sets the beam. |
| Lower TABs | 4, directly under the upper four | 36" lower (supplier minimum vertical separation is 24"). |
| Joists | 2×10 @ 16" o.c., run across the beams | Headers doubled at y = ±12¾" to frame the 24" × 24" trunk opening. |
| Cantilever | ≈ 46–47" past each beam | Backspan between the two TABs of a beam is only 25⅜". See load check and braces. |
| Knee braces | 4 × (4×6), ≈ 41° from horizontal | Lower TAB to the end of each beam, in the plane of the beam. About 55" between centers; cut ≈ 60" with mitered ends. |
| Deck | 2×6 PT, boards run along the beams | 21 boards with ³⁄₁₆" gaps; supported at 16" o.c. except 24" across the trunk opening. |
| Guard | 42" high, all sides but the stair opening | 4×4 posts bolted to the rim, 2×6 cap, 2×4 bottom rail, 2×2 balusters at < 4" clear. |
| Stair | 36" wide, 11 risers @ 7⅝", 10" treads | Closed risers. Attached to the platform rim, not the tree; foot rests on its own pad. |
Load check, not an engineering calc
Hand calculations with the stated assumptions, to show where the weak points are. They are not a substitute for review.
| Check | Assumption / result | Comment |
|---|---|---|
| Design load | 12 psf dead + 40 psf live = 52 psf × 100 sq ft = 5,200 lb | 40 psf is the IRC deck live load. Real use is a small fraction of this. |
| Per upper TAB | 1,300 lb if the four upper TABs carried everything | 16% of an 8,000 lb figure; 43% of the 3,000 lb low end quoted for Garnier Limbs. |
| Per TAB, all eight | 650 lb average if braces share the load equally | Real split depends on brace fit. |
| Joist (2×10) cantilever | ≈ 283 psi bending, 0.02" tip deflection | Allowable for SYP #2 is ~1,000 psi before wet-service reduction. Large margin. |
| Joist uplift at the far beam | ≈ 240 lb per joist with only the cantilever loaded | Tied with one H2.5A per beam crossing; confirm the tie’s uplift rating against this number. |
| Beam (doubled 2×12) cantilever | ≈ 373 psi bending at the TAB | Margin is fine; the issue is the support reactions, below. |
| Beam reactions, one end loaded, no braces | ≈ 1,930 lb down at the near TAB, ≈ 930 lb UP at the far TAB | Why the braces are in the design. The far TAB pulls out of the tree in this case. |
| Knee brace (4×6, ~55") | ≈ 1,980 lb compression if one brace took a 1,300 lb share | Far under a 4×6 column capacity; the brace bracket and its TAB are the limit. |
What this tells you: the lumber is not the limit. The limit is the connection between the platform and the tree, and the uplift case at the far TAB when one end is loaded. The braces exist to remove that case.
Lumber
| Part | Qty | Size | Notes |
|---|---|---|---|
| Beam plies | 4 | 2×12×10' PT, full 120" | Laminate two plies per beam with construction adhesive and ¼" × 4½" structural screws, two staggered rows at 12" o.c. |
| Joists, inner | 8 | 2×10×10' PT cut to 117" | At y = ±12¾" (doubled: 4 pieces), ±28¾", ±44¾". Seat in hangers at the rims. |
| Outer joists (N and S edges) | 2 | 2×10×10' PT, full 120" | Sit on the beam ends, flush with their ends. |
| Rims (E and W edges) | 2 | 2×10×10' PT cut to 117" | Fit between the outer joists. |
| Decking | 23 | 2×6×10' PT | 21 needed plus 2 spare. Cut the four center boards at the 24" opening (two 48" pieces each). |
| Knee braces | 4 | 4×6×8' PT cut ≈ 60" | Miter both ends to fit the bracket and the beam; measure on site. |
| Guard posts | 8 | 4×4×6' PT cut to 53" | Corners and mid-sides. Bolt to the outside of the rim/outer joist, 2 × ½" carriage bolts each. |
| Guard top cap | 5 | 2×6×10' PT | Flat on the posts. |
| Guard bottom rail | 5 | 2×4×10' PT | On edge, 3½" above deck. |
| Balusters | 45 | 2×2×8' PT, 2 per board at ≈ 34" | About 90 balusters, < 4" clear. Skip the stair bay (36"). |
| Stair stringers | 3 | 2×12×12' PT | Layout for 11 risers at 7⅝" and 10 treads at 10". Adjust to the real deck height. |
| Stair treads | 7 | 2×6×10' PT, cut 36" | Two 2×6 per tread: 20 pieces, 3 per board. |
| Stair risers | 4 | 1×8×8' PT, cut 36" | Closed risers to keep openings under 4". |
| Handrail | 2 | 2×2 or round 1½" × 10' | Graspable; 34–38" above the tread nosings. |
Cut ends of pressure-treated lumber get end-cut preservative. Use fasteners rated for PT lumber.
Hardware and materials
| Item | Qty | Notes | Price |
|---|---|---|---|
| TAB 1.25" (SD) 6×12, powder coated | 8 | Treehouse Supplies listing: 12" perch, 3–4" collar depth. Confirm size for a 16" oak with the supplier. | $241.95 each = $1,935.60 (listed) |
| TAB brackets / beam cradles for 1.25" TAB | 8 | Must accept a 3"-wide doubled 2×12 (upper) and a 4×6 brace (lower). Confirm with the supplier. | Check with supplier |
| Pressure-treated lumber (cut list above) | — | Big-box stock lengths | ~$1,700 est. |
| H2.5A hurricane ties | 16 | One per joist/beam crossing | ~$25 est. |
| Simpson LUS210 (or equal) joist hangers | 16 | Joist ends at the E/W rims | ~$50 est. |
| ¼" × 4½" structural screws | 1 box | Beam laminations, joist and rim corners | ~$80 est. |
| #10 × 3" PT-rated deck screws | 2 boxes | ~400 screws | ~$100 est. |
| ½" carriage bolts, washers, nuts | ~24 | Guard posts | ~$60 est. |
| Construction adhesive, end-cut preservative | — | Laminations; every cut end of PT lumber | ~$40 est. |
| Gravel, 2 precast pier blocks (stair foot) | — | Or concrete footings if the grade needs them | ~$100 est. |
| Total | TABs are the listed supplier price; everything else is an estimate for late 2026 and unverified. | ≈ $4,900–$5,500 est. |
TAB price from the Treehouse Supplies product page as listed on Oct 22, 2026 (sold-out sizes excluded). All other prices are rough estimates and not checked against current stock.
Build sequence
Phase 0 · Before buying
- Complete the gates above and settle the final TAB size and bracket with the supplier and the reviewer.
- Fix the deck height from the site survey. Everything vertical (stair, posts, braces) follows from it.
Phase 1 · Layout and tree prep
- Pick the beam axis so the stair lands on the uphill or flattest side.
- Keep soil unpacked and unpiled inside the drip line during the build. Stair footings go outside the root zone where possible.
Phase 2 · TABs (the part that matters most)
- Mark the four upper TAB positions at 45° around the trunk with a water level tube so all four are at the same height. Mark the four lower positions 36" straight below. Supplier guidance is a conservative minimum of 24" vertical and 6" horizontal between holes.
- Drill each hole with a 1⅛" auger bit for hardwood (supplier figure), to the depth the supplier specifies for the size you bought. Turn the TAB in with a 1⅞" socket on a ¾" ratchet. The nut goes on the outside end.
- Install brackets. Check that all four upper perches are level and square to each other before any wood goes up.
Phase 3 · Beams and framing
- Laminate and set both beams on the upper brackets. Level them, confirm 25⅜" center to center, and confirm at least 3" clear to the trunk.
- Lay the headers and joists across the beams, hang them at the rims, and tie each beam crossing with an H2.5A. Check the frame is square by measuring diagonals.
- Install the four knee braces with the beams level and unloaded. Cut and miter to fit rather than to the drawing.
Phase 4 · Deck, guard, stair
- Deck boards along the beams with ³⁄₁₆" gaps, two screws per joist crossing. Cut the opening 24" × 24".
- Guard posts bolted to the rim, then rails and balusters. Test every post by hand.
- Stringers, treads and closed risers. Attach the top to the platform rim. Rest the foot on its own pad so the tree can move without loading the stair.
Phase 5 · Test and sign-off
- Load the platform in steps with sandbags: ¼, ½, then full planned use. Measure beam deflection and watch the perches for movement at each step.
- Have the reviewer sign off. Then use it.
Every year, and after every big storm
- TAB nuts and brackets tight, no visible movement or cracking at the bark around the collars.
- Gap between each beam and the trunk still at least 3". Adjust or retrofit before the tree touches the beam.
- Beam, brace and joist ends: no soft spots, splits or loose fasteners.
- Deadwood, cracks and fungus on the oak. Call the arborist for any change.
- Clear snow, ice and leaves from the deck and stair before use.
Judgment calls and unknowns
TAB capacity
HighPublished figures range from 3,000 to 12,000 lb depending on the source, hardware model, tree and leverage. Treehouse Supplies says TABs are not assigned specific ratings. Oak is a strong species but this tree has not been assessed.
Brace side load
HighIn-beam-plane braces load the lower perches sideways as well as down. I have not analyzed this. It is the first thing the reviewer should check.
Cantilever
HighBeams and joists extend about 47" past supports with a 25⅜" backspan, which breaks the usual deck rule of thumb. The braces and ties are meant to cover it; confirm with the reviewer.
Permit
MedThe state exemption language names sheds and playhouses ≤ 200 sq ft. Whether an elevated platform with a guard and stair qualifies is for Roxbury’s building official. I did not find Roxbury treehouse guidance, and setbacks were not checked.
Deck height and slope
Med7'-0" is a placeholder. A builder cited above calls a platform over 10 ft “probably too high.” Stair length, post length and brace rise all change with the real height.
TAB size and brackets
MedThe 6×12 is priced here because it has the longest perch. The 3×9 is $173.95 each and its listing limits it to 1.25" brackets. Which is right for a 16" oak at this load is a supplier and reviewer call.
Tree growth
LowThe 3¼" gap to the trunk and 4" in the deck opening will close over years. Plan on retrofitting the beams before contact.
Stair movement
LowThe stair is fixed at the top to a platform that moves with the tree. A loose foot on a pad avoids loading it; it needs a look after storms.
Roof and walls
Out of scopeNot in rev 1. A roof adds dead and snow load on the same eight TABs and needs its own check.
Costs
Est.Only the TAB price is sourced. The total excludes the arborist, reviewer, and permit fees.