Treehouse Support Systems

Dan Wright explains cabling

A builder should look first to the tree to dictate what type of support system to use. If the treehouse to be built is more than a basic rectangular platform, the best choice for support is probably a flexible support system. The weight or size of the treehouse doesn’t necessarily determine whether joints need to be flexible or not, it is the tree. Flexible supports allow for the tree to move in the wind, lessening the stress of your structure. The biggest concern is when the building is done closer to the ground. The wind that a tree catches can swing the whole tree around quite a bit. In some parts of the world, the leaning and bending that a tree is subjected to is quite powerful. Nearer the ground, the trunk acts like a giant lever, magnifying the strength of the wind into an incredibly powerful force that only moves an inch or two.

Beams to be used in a spoked platform

An inch or two, however, is actually a relatively large movement, translating to a force that’s large enough to lift a ton of weight. A fixed system will be under immense pressure, and will easily break. If a treehouse will be subjected to these type of forces, a flexible system is the way to go.

When a support system employs one end of a beam that is fixed while the other end allows for tree movement, there is no build up of pressure and the platform will withstand strong movement. During a violent storm or high winds the treehouse itself may get damaged, but that is a design concern specific to the house and not to be confused with tree movement. When in doubt ask a professional builder or structural engineer.

Building the Platform

YELLOW LIGHT
If you have any doubts about what bracket to use don’t hesitate to run your plan by an engineer familiar with treehouses. Let them give your plans a solid review for just the cost of a few hours time. A few dollars spent beforehand could save a lot of money and frustration down the road.

Octagonal Platform Undercarriage

Bolts and Special Fasteners

Let’s get to the “nuts & bolts” of it, shall we? Dreaming up your fantasy treehouse is a great thing to do, even sketching it out or rendering it in photoshop. But, when it comes to building it you better know your fasteners and what works for you and the tree(s) you’ve chosen to place your vision into. New and innovative braces and fasteners are being developed all the time. Something about treehouse building lends itself to innovation. In addition to imaginative designs and creative uses of materials, new braces and fasteners are making an appearance as well.

Michael Garnier, famous for his “Garnier Limb,” continues to develop new and better supports, including floating limb applications and sliding brackets. In addition to writing an invaluable book, Treehouse Chroni-cles, S. Peter Lewis has pioneered the use of innovative “shouldering bracing.” Charlie Greenwood, a trained structural engineer, tests his support system ideas on a tree-house in which he lives fulltime. His latest innovation is the “heavy limb” which can support huge beams. I spent time on the phone with Charlie and his command and understanding of the engineering side of treetop design is unparalleled. These are just a few of the really terrific things that are happening in the treehouse world with many more to come.

OK so here are some practical tips. I suggest you glance over and research any of the people and ideas I bring up so you fully understand the innovations and techniques.

Garnier Limb

An invaluable contribution to treehouse design by builder Michael Garnier, the “GL” is the most commonly known of all the “attached limb systems,” or tree bolts. It’s capable of withstanding significant shear forces, better than any hardware previously used. The basic GL is made from machine threaded, one-and-a-quarter inch steel round stock with a unique flanged collar. Once installed, the bolt can withstand loads from eight thousand to thirty thousand pounds. http://www.treehouses.com

Shoulder Bracing

A unique design pioneered by S. Peter Lewis. The support system he used in his dream treehouse is described as follows;

A collar made of six pieces of angle-iron is fastened at the corners with welded eyebolts, forming a hexagon.
Five cables attached to the eyebolts loop up and over the tree fork. The cables run through PVC pipe to protect the tree.
From the suspension collar, a hexagon-shaped platform formed by trusses is held tight by an interior and perimeter rim joist.
The trusses are built of hefty, five-by-five inch hemlock from local mills. The complete chronicle of his treehouse building adventure can be found in his book TREEHOUSE CHRONICLES: One Man’s Dream of Life Aloft. http://treehouseguy.wordpress.com/

Heavy Limb

A wood interface much like a large GL, “HLs” have threads that are wider and more deeply pitched. They are ideal for supporting heavy beams and long knee braces. The “limb” can be as long as necessary through the building of extensions. “Arrestor Brackets” can be used with HL’s, allowing the tree to continue to grow and move. For more go to http://www.treehouseengineering.com/