Ever wanted a closer look at how the Nelson Treehouse crew attaches the treehouse to the tree?
The magic lies in the Treehouse Attachment Bolt, or TAB. This heavy-duty piece of hardware is one of the most important structural elements of treehouse building. TABs are made of hardened steel, and act as artificial tree limbs on which the main structural support members of the treehouse rest or hang. When installed correctly into the trees, a Standard Limb TAB can support between 8,000 and 10,000 pounds of force (softer trees like Pines and Cedars support less force, while harder trees like Oak and Hickory support more force).* TABs are unequivocally the best way to attach treehouses to trees.
*Note: These limits are conservative estimates, not precise weight ratings. We tested the weight-bearing capacities of TABs at Washington State University last fall, and can't wait to share our findings with you. Stay tuned for the results - we'll be posting about it soon! In the meantime, we're providing these conservative figures for how much force our Standard Limb TAB can support.
Not only do TABs support large loads with ease, they also allow the free growth of the tree.
In other words, TABs do not harm trees! Unlike girdles and chains that wrap around the circumference of trees, TABs do not choke or damage their living hosts. The tree reacts to a TAB by growing wood around the perimeter of the boss (the central component of the TAB). This seals off any possibility of airborne fungus or disease infiltrating the tree. Nutrients continue to flow through the essential cambium layer of the tree, located just below the bark, and the tree continues to grow in its normal fashion. Happily, as the tree envelops the TAB, the hardware becomes stronger and more secure.
TABs are made of of two separate pieces of steel, and consist of four main sections: the coarsely threaded end, the boss, arm, and short threaded section (see Figures 1 and 2, below). The coarsely threaded end secures the TAB into the heartwood of the tree. The boss, the thicker piece of 3-inch diameter steel, provides the majority of the TAB's sheer strength and allows for greater distribution of the load. The arm extends outward from the boss and acts as a limb to support beams or other structural elements. At the end of the arm is a short threaded section designed to accommodate a K-nut. We fabricate our TABs with a local Seattle machinist. You can find the perfect TAB for your treehouse here at Be in a Tree.
--- FUN FACT: Did you know that trees grow upward from their tips, not the base? ---
This natural growth pattern allows TABs to remain at exactly the same height where we installed them; it's also the reason why treehouses don't move up as the tree grows taller. Trees also grow in girth all along their length. We design our TABs to have long arms so that as the tree grows in width, it can incrementally push the beam out along the arm without destroying the treehouse. Pete can attest to the longevity of TABs; he used TABs to build each of the treehouses at TreeHouse Point over ten years ago, and both the trees and TABs are just as healthy and strong today as they were then!
Last fall, we had the opportunity to test the weight-bearing capacities of our hardware at Washington State University.
We'll be bringing you the astounding results on the blog sometime soon. Make sure to subscribe to our mailing list so you're among the first to find out about it! In the meantime, we can tell you this: although we already knew that TABs could support thousands of pounds of force, we were blown away by just how great a load our TABs successfully endured in the testing!
What's the story behind the TAB?
In 1997, arborist and builder Jonathan Fairoaks brought a treehouse attachment device to the annual World Treehouse Association Conference in Oregon. This device was a three-inch diameter stainless-steel pin that, when sunk into the heartwood of a tree, was able to support far more weight than anything we had attempted thus far. Jonathan's device caught the attention of Michael Garnier, host of the conference and renowned treehouse hotelier. Over the course of the next year - and with the help of his head engineer, Charley Greenwood - Michael refined a tree-bolt design that came to be known as the Garnier Limb, or GL. The GL evolved into what we now call the TAB. If you're interested in more details about the illustrious evolution of TABs, check out the full story in Pete's books, Be in a Treehouse and New Treehouses of the World.
Wondering how to install a TAB?
Luckily, Daryl's here to guide you through the basics of TAB installation. Check it out in the video below!
If you like this blog post on the nitty gritty of TABs, we think you'll really enjoy Treehousing: The Instructional Guide. We get questions all the time about the fundamentals of treehouse building, and we always refer folks to this handy dandy guide - every treehouse DIYer needs to know about it! If you're tackling your own treehouse and need more technical information on treehouse hardware, tips for platform design and build, and advice for selecting the right tree, Treehousing is the perfect guide book for you. By the way, we send you a FREE copy of the guide when you order any of our treehouse plans!
We hope you've enjoyed learning about the miracle that is the TAB! Let us know in the comments below which type of hardware you'd like us to highlight next. To stay updated on all our blog content, subscribe to our mailing list and give us a follow on social media.