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The World Needed a better Treehouse Fastener
It was the arborists who got the conversation about better treehouse fasteners started. Back in the middle 1990's, Jonathan Fairoaks realized that the tree houses that Peter Nelson was building at the time were causing excessive harm to the trees. He drove up to Seattle to meet with him because something had to be done. The search for better fasteners for tree houses had begun.Before long, Michael Garnier (treehouse builder & treesort operator) and Charlie Greenwood (Engineer) joined the conversation. Garnier, Greenwood, and Fairoaks are generally credited with the creation of the original garnier limb. It is hard to tell just who should receive what share of the credit for the creation of the original Garnier Limb tree house fasteners. They all three tell the story just a little differently. The part that is clear is that they each contributed to the brainstorming process and produced prototypes for testing. Since no patent was applied for, the final design was not owned by any of them. However, it was given the name, "Garnier Limb" in honor of Michael Garnier who is generally considered a true tree house pioneer.
The Evolution of the Garnier Limb
The original Garnier Limb was a 5/4" steel stud about 12" long. It had a 3" diameter collar pressed onto the middle of the GL that was about 1/2" thick. Some of the other varieties were better, some worse. Early on, there was much discussion related to the cost versus the strength of various garnier limbs and other related treehouse fasteners.
One early modification was the "poor man's" GL. A diminutive term for what was obviously a much cheaper and less reliable version. Instead of solid steel rod that had threads ground on, the poor man's garnier limb used some B7 grade all thread rod, and some steel washers with 5/4" inside diameter were welded onto the center to replicate the collar. Needless to say, the all thread is not nearly as strong as the solid rod and the washers tack-welded were not nearly as strong as the collars pressed onto the garnier limbs. They were cheaper, but not enough cheaper to warrant using them under any circumstances. To our knowledge, these were never approved or used by any engineer.
Rather than leaning toward cheaper garnier limb designs, most professional tree house builders leaned towards more expensive, but larger and stronger models. The first improvement came when the fasteners started getting heat treated and powder coated. The heat treated steel garnier limbs were so strong that they usually did not fail under normal loads, but rather, the wood of the trees failed! The loads would force the collar through the cambium layers of the trees! In order to give the garnier limbs more surface area of tree to press against, the collars gradually grew from 1/2" thick all the way to 6" thick. Beyond that, some heavier diameter rods & collars have been used in tree house fasteners called HLs. These are primarily used in commercial tree house applications. Needless to say, you also need a big tree to put that much steel into it.
The Future of Treehouse Fasteners
It's hard to look into the future when the Garnier Limb type fasteners for tree houses are so well accepted and widely used. Between the garnier limbs and some large diameter lag bolts, today's treehouse fasteners are sufficient for applications in most small to medium tree houses. But there are always those who push the limits, and they will probably be the ones to make the next break-through.
Perhaps it is more meaningful at this time to discuss modifications that can be made to garnier limbs to make them more useful, longer lasting, and safer during tree movement. Some GLs are being tweaked to make future adjustments easier, lengthening the lifespan of the tree houses. Another area for development is in the brackets that attach the beams to the garnier limbs. More focus should also be given to making GLs, tree house fasteners, and the various brackets easier to install.