Years ago I asked a friend who was pretty handy with a hammer and saw how to build a tree house. He gave me three rules:

1. Try to use materials you have on hand.
2. Get the kids involved.
3. Use cantilevers.

Great, I thought, what’s a cantilever?

Turns out a cantilever is just a beam supported only on one end. If you look at the balcony that hangs out in midair on Frank Lloyd Wright’s Fallingwater house, it’s held up by cantilevers. The only problem was I was building a tree house for kids, and I’m not Frank Lloyd Wright, and I didn’t want small children hanging out in midair, so I thought it best to add some support beams – trusses, they’re called. I realize that this is beginning to sound much more complicated than it really is, so let me explain what I did.

First I ran two two-by-eight-foot beams – one fastened to each side of a big oak tree with six-inch lag screws – horizontally out from the tree and about eight feet up the trunk. Then I supported each of those beams with another two-by-eight that ran from the end of the horizontal at about a 45-degree angle back down to where it was lag-screwed into the tree. Basically this formed a triangle under each beam, sort of like how a bracket holds up a shelf. And it’s remarkably strong.

Yes, I realize that I could have also used posts that dropped straight to the ground from the ends of the horizontals, but then I wouldn’t be able to say, “I used cantilevers,” would I?

Another classic construction method is to build the house between two trees, using each of them for support. But if you do this, be sure not to bolt any board directly to more than one tree. Bolt one end and hang the other with steel cables. Trees tend to sway in the wind and anchoring the house to two of them could easily break it apart.

Once the horizontal beams were in place, I laid two-by-four-foot studs across them and then nailed pine boards over the studs to form a deck. What you build on your deck is entirely up to you and if you look online – try www.thetreehouseguide.com – you’ll see that the only limit is your imagination. Tree houses run the gamut from simple shacks to mini trophy houses you’d expect to see in Architectural Digest.

With the help of my son, who was eight years old at the time (remember Rule Number Two), I built a simple shed-like structure on top of the deck. One wall frames a big limb that actually juts out through the house. And in deference to Rule Number One, I used pine boards leftover from some remodeling we had done. But if you do use available materials, be sure the lumber is not rotten and that it does not have too many knots, and don’t scrimp on the support beams. It is after all a tree house, and your kids are going to be playing in it, so make sure it’s safe.

You could also do what West Tisbury contractor Bill Dreyer did; he used actual trees for his tree house. First he found a tree that had a cradle formed by the trunk and two large branches, and he nestled his deck right in there. Then, for added support he used posts cut from trees with the bark left on them. It’s more of a tree fort than a tree house; there are no walls, just a guardrail made from tree branches. And because of the natural materials, it blends into the forest very unobtrusively. As Bill says, “It’s funky. I did it in a day and the kids were great at helping design a pulley system that hoists up a big bucket.”

Another variation on the tree-house theme was built by Kyle Carson and his son, Oliver, at their Oak Bluffs home. The top half of a tree snapped off in a storm, so Kyle decided to build a tree tower. He got unfinished boards from a lumberyard and used them for posts to support a deck about eighteen feet up, where the tree broke off. He then built a circular staircase going to the top, sort of like you’d find in a lighthouse. He used bittersweet vines as handrails.
The point is, once you’ve constructed and supported a deck, the variations on building your tree house are endless. As Kyle says, “The tree really suggests how the structure should be built, just go with the flow.”