This particular design requires two or three trees (or branches) in close proximity. It was made over the course of several weekends using new, pressure-treated wood for the support structure and floor and an old fence was recycled for the sides. The roof is a camouflage-pattern tarp. It's not weather-proof, but it stays pretty dry inside: a three-season treehouse, but best for summer! It was made with my 4, 6 and 8-year old children in mind, but has been a hit with visitors of all ages.
Step 1: Pick your trees
There are definite advantages in using more than one tree for your treehouse - the treehouse can be bigger, and you have to use less bracing. The tree(s) you see here (behind the magnolia!) are a very tightly grown group of three trunks - they all touch at the base, and splay out somewhat as they grow upwards. At the height of the treehouse - about 9 ft (2.7 m) off the ground - one pair of trunks are still almost touching, and the other one is about 4 ft (1.2 m) away. This means the design has been based on one for a close-spaced pair of trees, rather than for a group of three. The trees are Garry oaks, and they don't grow much further north than this (southern Vancouver Island), so they grow pretty slow here. A solid gnarly collection of old trees, each about 1 ft in diameter at 9 ft up.
Start by figuring out how high you want the treehouse. 9 feet is exciting for kids but not scary. You can of course go higher, but you'll have to take more account of movement.
Step 2: Get your materials
For this treehouse, I bought:
2 x 10' lengths of 2 x 10 pressure treated (PT) lumber.
6 x 12' lengths of 1 x 6 PT decking material.
6 x 8' lengths of 2 x 6 PT lumber.
3 x 10' lengths of 2 x 4 PT lumber.
4 x 6" long, 1/2" diameter galvanized lag screws and washers
1 x 8" long, 1/2" diameter galvanized lag screw and washer
8 galvanized joist hangers
8 galvanized rafter ties
Nails, deck screws, pulley for 1/4" rope
All this cost about $250 from the nearby Home Depot. The rest of the materials came from a neighbour's old fence: plentiful amounts of cedar boards and 2 x 4 lumber. It was used for the sides, so you can just substitute whatever you'd like to make a railing/walls.
The photo is of my plan, which was sketched on a cereal box. I read around a lot first, of course: I found David Stiles' books
especially easy to follow. The design changed as I was building it - I didn't end up adding the braces drawn in the bottom left elevation, and I built an entranceway platform that I hadn't originally planned.
Step 3: Get your tools
The bare minimum of tools:
A ladder is important, but even a stepladder would be OK if you installed a ladder/rope ladder/stairs to the treehouse early in the build.
Useful power tools:
Jigsaw (cutting decking and the movement-accommodating slot)
Cordless drill (driving screws)
Compound mitre saw (cutting lumber to length)
A jigsaw is probably the most useful additional power tool. I used the router to round off some edges, but coarse sandpaper and some elbow grease would work just as well.
Step 4: Mount the main supports
Get a strip of light wood and nail one end to one of your trees at a height about 1 ft lower than you want the floor of your treehouse (to save a future concussion, it should also be at least 1 ft higher than your head!). Get it perfectly horizontal with the help of a level and nail the other end to the other tree. Drill 3/8" holes straight into the tree just above the strip of wood. Do the same on the other side of the trees, this time taking the extra precaution of first ensuring the new strip is not only horizontal but also level with the strip on the other side of the tree.
Now, take down the strips and measure the exact distance between the holes. Subtract this distance from 10', halve the remainder, and make a mark this distance away from one end of your 2 x 10. Drill a 5/8" hole in the middle of the board. Make another mark using the between-the-holes measurement . Now drill two 5/8" holes, each 2" either side of your mark and both in the middle of the board. Get a jigsaw and make two cuts between the holes to make 4" long slot. Repeat for the other side of the tree. The slot allows the trees to move without tearing your treehouse apart - the more your trees move, the longer the slot ought to be (note that the slots I cut are only about 2" long, not 4", but these trees don't move perceptibly at the height of the treehouse, even in a strong wind. If your trees move appreciably, and/or if you're planning to build higher up, use a sliding beam support
Now, screw your boards to the tree with a wrench. Use washers, and don't bolt hard against the tree. The space you're giving it to grow is the gap between the support and the tree. The longer you want your treehouse to last, the further you should perch the support away - and the more substantial your lag screws ought to be! 3/4" or, ideally, 1" would be best.
Step 5: Lay out the platform
Because the decking came in 12' long boards, I made the treehouse 6' long. So you need to cut the decking in half, and lay it out. Leave a 1/2" gap between boards for drainage. Cut two of your 2 x 6 boards the same length as the decking, and the other four to the width of your decking less the thickness of two of the 2 x 6's (which will be more like 1 1/2" each).
Step 6: Build the platform
Using 3" deck screws, attach the four 2 x6's perpendicular to one of the other 2 x 6's. Make sure they're spaced so that when you put it up in the tree, the perpendicular joists will miss the tree! With someone's help, put the contraption up in the tree, center it, and tie it down.
Step 7: Finish and square the platform
Screw the other 2 x 6 to the other end of the platform, and check that it is centered and square.
Step 8: Attach platform to supports
Now use the rafter ties to attach your platform to the 2 x 10s that you screwed to the tree (if the angles between joists are not exactly 90°, no problem, just hammer the rafter tie flat against each joist as you're nailing). Add the joist hangers. Use galvanized nails to attach these, not screws.
Step 9: Brace the platform
As it is, the platform will wobble. Add diagonal bracing made of 2 x 4, and use a single long lag screw to attach both of these to the tree. It's easiest to just cut the 45 degree angle in the 2 x 4 first. Use an 8" lag screw here to make up for the fact that you're going through 2 thicknesses of lumber.
Note that I just used one set of braces on the single tree, because the other end had two trees and the wobble seemed insignificant. You'll need two sets for sure if you have just a pair of trees.
Step 10: Hang a pulley
A pulley is great fun for kids, but it's hugely helpful for hauling tools etc. up to the deck. Put one in now, and hang a bucket from it. A hefty climbing carabiner at the end of the rope is perfect.
If you don't have a suitably overhanging trunk or branch, you'll just have to make one. Lag screw a 2 x 4 between the two trees well above the deck (cut a long slot to accommodate movement, because you're higher up the tree), and have it protrude far enough to hang the pulley from. Bonus: you'll also have a ridgepole for your roof!
Step 11: Lay the deck
Get up on your platform and put down the deck. The only tricky thing here is cutting around the trunks - leave a 1-2" gap all around. I used a compass (the type for drawing circles) to mark the jigsaw cuts.
Having a few ladders around is definitely handy!
Step 12: Add an entranceway
OK, so far the build has been very conventional - all the books on treehouses will tell you how to get this far. One of my favorite bits was the following minor innovation. The two big supports poke out far past the platform, and you can use one set of these to make a slightly lower level to use as an entry. Make a small deck between the tops of the supports to about 2' out, then build diagonally back to the corner of the treehouse. Add verticals. The pictures tell the story here. I just used offcuts - with any luck you'll be able to do the same.
Some of the offcuts came from cutting the excess 2 x 10 supports off flush at the other end of the treehouse.
Step 13: Railing
I had lots of 2 x 4 from the recycled fence, so I used two 40" lengths at each corner as uprights. I screwed them to each other first then nailed them to the platform. The handrail was also 2 x 4, laid flat, and nailed straight down into the uprights. I mitered the corners, and screwed the handrails to each other through the miter.
Step 14: Sides
Use whatever you like to fill in under the railing - rope, plywood, whatever. Kids probably shouldn't be able to slip through, though. I had lots of nicely weathered cedar boards which I just nailed up with gaps between. I used strips of 1 x 1 to hold them in place either side under the railing. The only tricky bit was the angled bit leading down to the platform - a bit of trial and error here, because it is tricky to line up the railing with the sides of the platform.
Step 15: Ladder
The plan was to use a rope ladder to get up, but my 4 year old struggled with the transition to the platform, even though he could climb it just fine. So we vetoed it, even after making a really nice ladder (perhaps the subject of another instructable). I leaned a couple of 2 x 4s against the entryway, cut the angle, and nailed on two thicknesses of cedar board all the way up. The plan was to make a climbing wall, but I was shocked to find out how much the hardware cost - about $100 for 20-odd hand grips - so I just cut foot/handholds instead. I'd like to say this was free, but I wore out a big spade bit cutting the holes - it got too hot, and bent. This job was easy if a little time consuming to do - mark and drill two big holes, mark a line between them at the bottom and an arc at the top (I used a plastic bucket) and cut out with a jigsaw. This had really rough edges, so I rounded them off with my little router. That worked great, so I went around quite a few other edges on the treehouse with it. Smooth!
Step 16: Roof
I just strung a bungee cord between two hooks I put into the trees at about 7' above the deck, and slung a tarp over. This looked good, but in actual fact it made the roof too low at the sides. I have a compound mitre saw, so I cut four outriggers, screwed them to the uprights, and gave the treehouse roof a decent overhang.
Step 17: Enjoy!
The treehouse is a great little (36 sq. ft.) haven for the kids; they love it and so do all their friends.
I'm happy to report the treehouse is four years old now, it's suffered no damage from windstorms, snow, or tree growth, the trees are healthy, and it still gets lots of use. We've made a few updates over the years, adding a pirate's treasure chest
, a swing, a braided climbing rope
, a BEWARE sign we use out front at Halloween, and it's well-equipped with Nerf guns & water pistols. It's just big enough for two single air mattresses, so it's fun to sleep out in, too.