Deck Foundation

As most of the deck of the treehouse will be hanging out to one side of the main support tree, I had to figure out a way to support it using the tree itself somehow, and not resorting to additional support posts. The simplest and most evident manner appeared to be using a single main 'outrigger' beam to provide support for the four floor beams away from the tree. This beam would then be supported by two angled brace posts which would then be attached to the trunk of the tree very clost to the base. I decided that this support should be angled in the same direction as the support posts, pretty much 45 degrees from vertical. I constructed four small angle blocks to support this beam (one block for each floor beam supported by it). In addition, I cut a small 1-1/2 inch notch in each floor beam to accommodate a very secure attachment of the main beam to each of these floor beams. Check out the pictures, which shows the detail very well!

Uncle John's Tree House

While we were up at the cottage on March Break, John decided to repair the tree platform he had built for his children about ten years ago. It was a great time to get together for a beer, do something fun and useful, and let Rudi play with his cousin Natalie for a while. The platform was robustly built off of two white spruces, with a step ladder up, railings around, and a slide off the side. Although it was very well built, It was not designed with a foundation system that would accommodate the growth of the trees, and of course these two little trees packed on quite a bit of girth over the course of their lives. His goal was to rebuild the foundation in a manner that would accommodate all future growth of the trees without causing any futher damage to either the platform, or the trees.

The original foundation was incorporated into the floor joist framework, and consisted of a rectangular box built around the two trees. Over the years, the trunks grew outward into the box, and eventually pulled the box apart. The new foundation consists of two 2x8 beams that are lag bolted into the trunks, one at the front and one at the back of the trees. The joist framework that supports the floor deck now simply rests on these beams, and the beams are free to slide under the joists as the trees grow. The first and second pictures show the right hand tree, along with one of the old floor joists, as well as the two new main beams underneath. Notice on the trunk the depression left by one of the (now removed) 2x6 joists making up a portion of the foundation. The third picture shows both main trunks, as well as the front main beam, two existing floor joists on each side of a new 2x6 floor joist we installed.

Engineering or Art

Yes. Neither. Both. Hey, does it even matter? The following two photographs show the custom wooden bracket attachment to the smaller tree (note the spreader block installed to keep the longer clamp blocks from snapping as the bolts are tightened), and the simple 3/4 inch through-bolt attachment to the larger tree. Evidently the bolt will break at around 14000 lb under tension, so I am guessing there shouldn't be a big problem holding the treehouse up. The wooden bracket on the other hand...... In the spring, I will want about a dozen male volunteers to climb up and walk around the treehouse in a group, and if it doesn't fall down, I thnk it will be fine!

Research and Planning

I think I have had sufficient time to research treehouse design and construction. Over the last 6 years or so, I have read (and re-read) about six books completely dedicated to the subject, and more recently visited a number of websites as well. In general, the information I found was very useful, and has certainly cleared up any misconceptions I may have had about the best manner of construction.

It seems the two most basic rules of treehouse construction are to keep potential injury to the tree to a minimum, and to make sure your design accomodates future growth of the tree.

A treehouse should be attached to the tree with the least number of connections (threaded rods, lagbolts, brackets, or wooden clamps) as possible, and these connections should be large enough to easily support the load of the treehouse and its visitors.

With respect to future growth of the tree, any attachments must be designed in such a way that the year by year growth of the tree doesn't end up breaking the supports or "foundation" or pushing the frame away from the tree.

The design I finally decided on will use two trees, the first for a small platform, and the second around which the treehouse will be built, with a walkway between them. This means that the main support frame fixed to the trees could not have a rigid connection. If you look closely at the picture in the next post, you will see that the main support frame is bolted directly through the larger of the two trees, and then just rests on a wooden bracket on the smaller tree, and can slide back and forth as the trees move in the wind.