I love this tiny treehouse, which is essentially a single-tree structure with a bit of a boost from a neighboring tree, attached with paddle TABs and supported by knee braces. It could use a bed for napping, but other than that, it is perfect. The Sitka spruce host is the best part, of course, but the house’s scale and size feel just right. We call it the Hermitage in reference to the simple rooms or huts that monks would use, and still do, to practice their devotions. In this case, hanging 15 feet above the clear waters of the Raging River, it feels like you are in a miniature church devoted to nature.
The Hermitage is equipped with a hinged ladder system and the rugged exterior is salvaged from the broad roof shingles of a local barn.
A simple desk awaits the explorer at Treehouse Point, a place we hope inspires creative thinking and thoughtful reflection.
Charley Greenwood, treehousing’s groundbreaking engineer, stopped by in the earliest days of Treehouse Point to put his stamp on the plans for our first treehouse, the Temple of the Blue Moon. It was planned as an off-center single-tree design that, in the end, took advantage of a second tree to share the load. The main tree is a mature Sitka spruce that is 39 inches in diameter at floor level. A tree like this could surely sustain the weight of the 17-by-17-foot treehouse that I had designed, but, as Charley pointed out, if there is another tree directly in the vicinity, use it.
Hence, a two-tree platform design was used. Since the spruce projects through the treehouse close to the corner of an almost square plan, knee braces are used to keep two of the farthest corners raised and level. Adding a second tree to the plan allowed room for a small outside deck—a feature no treehouse should be without.
The twin yokes supporting the main beams are made of wood and steel. This allows for easy adjustments in the field, as the angled struts can be cut with a saw to fit any situation. Most of the struts that I use today are carefully measured and fabricated off-site using steel.
A mature Sitka spruce carries the majority of the load of the 290-square-foot treehouse. Additionally, the 25-foot bridge is secured back to earth with heavy-duty helical screws that are more often used to anchor electrical towers.
Twin yokes are used to spread the distance between the two main support beams.
This creates more room for the trees to grow and helps balance the weight of the structure above.
The side-mount design of the Trillium treehouse came about for two main reasons: First, one side of the host western red cedar was tight to one of the main buildings at Treehouse Point; and second, the cedar is massive (46 inches in diameter at 16 feet off the ground), so the idea of side-mounting a 200-square-foot, two-story treehouse was a thrilling challenge. We accomplished it with knee braces but no posts. It offered a rare opportunity to build a structure in this way, so I present this for the purpose of showing the possibilities. It was completed in 2008 and both the tree and the treehouse are going strong.
Trillium was designed in the spirit of a timber-frame structure. The connections are all steel, however, and not the classic mortise-and-tenon type that are true to the timber framer’s art.
The soaring two-story structure sits on one side of a massive western red cedar supported by two knee braces
and some high-strength cable that keeps it snug against its host.
If your trees are big enough, this two-tree main support system is a great way to go. It is a classic design for a common scenario. In this case the two main support trees, both western red cedars about 24 inches in diameter at floor height, are 15 feet apart. Four TABs support two beams, which sandwich the trees. In the end, there is an area nearly 3½ feet wide on which to balance the joist level. The joist level is what carries the floor surface.
It is important to point out two features in a design like this. First, as trees move in the wind, beams must be installed in a way that allows for the trees to move independently without tearing apart the platform. Using static uplift arrestors (SUAs) in combination with dynamic uplift arrestors (DUAs), as described in the next chapter, we make one tree act as the anchor for the platform, while the other tree allows the forces of lateral motion to release.
Second, sandwiching two trees with beams in this manner often creates a narrow center of balance for a platform, necessitating additional support at its cantilevered edges. Balancing the load can be accomplished with posts to the ground, or, more appropriately perhaps, knee braces back to the trunks of the trees. This is important to the integrity of the treehouse platform and adds a critical layer to the project.
As the treehouse is accessible only by a ship ladder, guests use a pulley system to bring their luggage up to their sleeping quarters.
An elegant solution to the two-tree scenario that creates a wide center of balance is to use yokes. A good example of this is Bonbibi at Treehouse Point.
In the twenty-five years that I have spent working in the trees, the steel yoke system, described in the next chapter, has risen to my top choice as a practical, low-maintenance, and effective method of attaching heavy loads to living trees. It works for many reasons: It is strong, it is flexible, it will last for generations, and it makes building a platform easier and safer.
Bonbibi, named after the Bangladeshi goddess of the forest, started out as a small elevated pavilion from which to look out over the woods and river beyond; we called it the Greek Gazebo. It was the centerpiece of a spring treehouse-building workshop in 2010 and was largely completed in five days. Judy, who runs the bed-and-breakfast, suggested that it be turned into an overnight accommodation. A remodel ensued. The ship’s ladder was replaced with an impeccably crafted spiral stair by the great treehouse carpenter Bubba Smith, and an all-out effort was made to make it comfortable and cozy. Today, a small deck with room for two hangs from the beams, sheltered from the elements by the house above. The upstairs feels like a stateroom in a 1930s lake-boat cruiser. There is room enough for a queen-size bed and a place to tie your shoes.
The beam layout is not perfect, as the original design was intended to accommodate a 9-by-9-foot pavilion, not the 9 by 12 feet it was stretched to become. It is a good example, nonetheless, of how a two-tree parallel yoke system works. One of its main attributes, aside from the structural advantage that a yoke allows, is how little maintenance is required once it is installed.
The yoke is a custom-fabricated steel triangle that is mounted to the tree with two TABs. The main purpose of the yoke is to separate two beams that would otherwise have to be flush to each side of the tree, creating a narrow balancing point for the structure above. Because the top cord of the triangular yoke separates the beams by 5 to 7 feet, the platform above has more support than if the beams were only separated by the width of the trees. It makes building on top of the beams easier and safer, and it can also eliminate the need for knee bracing back to the tree or posting down to the ground at the perimeter of the structure.
As in the Upper Pond treehouse, one tree acts as the anchor, and the other tree allows the forces of lateral motion to release. This adequately handles tree movement in the wind, but what about tree growth? Hang on to your hammers, because the answer is surprising.
Let the trees grow and absorb the yokes! This is new thinking, but it makes the most sense. Rather than imagining that the tree will grow and push the yokes away, like a sidewalk lifted by a tree’s roots, for instance, imagine instead that the tree will envelop the yoke and grow around it. It will do this readily when the yoke is bolted tight to its TABs. Meanwhile, the beams are now well away from the tree’s growth area, reducing maintenance worries, narrow balance points, and knee bracing. It is a win all the way around. All you need to do is flash the ends of the beams that are exposed to weather, an important task in any scenario.
The Bonbibi is balanced on two steel yokes. The yokes spread out the load and allow for tree growth and movement in the wind.
A small deck hangs from the beams below and uses the treehouse itself to shelter guests.
In its prior life the Bonbibi served as a gazebo. Still in evidence is the heavy-duty platform for participants in a building workshop observing the construction, installed in order to protect the forest floor from root compaction, which can be detrimental to a tree’s health.
The idea with this structure was to place it at a height that no one would notice—unless they looked up. When I take people on tours of Treehouse Point I purposefully walk by the Bird Blind until you practically bump into the ship’s ladder that rises off the forest floor. That’s when people notice.
This 80-square-foot wildlife observatory is 21 feet off the ground in a curious combination of two marvelous trees. A 30-inch-diameter western red cedar stands up straight and tall, and a 22-inch broadleaf maple blends seamlessly at the cedar’s base and stretches easterly to the river and the sunlight. It is a pair of trees that I could not resist, and in 2011 we planned and built a simple, if unusual, side-mount platform design.
Twin beam and brace supports hold the three-season structure off the unusual union of a broadleaf maple and a western red cedar.
The biggest tree on the property is a 200-foot-tall, 5-foot-diameter Douglas fir. If we were going to build a treehouse in it, it had to be extra special. We decided to incorporate a 40-foot-long bridge for access, because the topography at that particular spot begged for one. And who doesn’t love a bridge when they get the chance to build one?
Call in the engineer.
My only request to engineer Charley Greenwood was that we go with a steel substructure. We had just completed a similar steel design (John and Alex’s Serious Treehouse; see this page), and I liked the lower profile of what would otherwise be broad and unsightly beams and bridge stringers. As I am not skilled in the steel fabrications trade, the only thing I didn’t like was the bill.
Over the course of the next ten months, a revolving team of the building crew bit off parts and pieces of the enterprise. Daryl McDonald directed the steel assembly, Toby Malloy the framing, and Bubba Smith the interior finish. Devin Hanley worked on the roof and exterior finishes, and also had the dangerous job of directing and installing the stairway to heaven—a series of 10-foot-long steel ladder sections that stretch to a crow’s nest 144 feet off the forest floor. That part was for the television show, and as I am not big on heights, I’m afraid Devin’s next job on the Burl will be to remove it. It scares the pants off me.
Plumbing the Burl was a particular challenge. Getting water and electricity to a treehouse is in many ways the same challenge as getting water and electricity to a regular house, and depends on the climate you are building in. Building in cold climates requires forethought in keeping pipes from freezing—a surmountable problem. Getting waste and gray water away from a treehouse to a septic system is usually a matter of gravity. In the case of the Burl, however, Bubba installed a complex, albeit common, system that puts everything under pressure and pushes it across the bridge and another 100 feet to a septic system. It seems Bub has taken his already extraordinary finish skills to a new level. I wonder if he wishes this newfound trade of his to be known as a tool in his considerable toolbox. Something tells me he would rather keep this to himself.
A massive Douglas fir and sister hemlock take center stage at the Burl treehouse. One of the difficulties in designing a treehouse is not overwhelming the trees themselves—here that was very hard to do.
A view from the chairs out the small French doors that open to a covered deck.
The writing desk is a slab of old-growth cedar that had been kicking around in my shop for years.
By incorporating steel, the support structure has a reduced profile, creating the illusion that the treehouse is hovering in space.
