Engineering:Treehouse attachment bolt

From HandWiki
A Garnier limb (GL)
Early GL Prototypes
An example of tree growth over time, enveloping an older GL, beam & bracket

Treehouse attachment bolts or TABs are specialized bolts engineered for treehouse construction.[1][2][3] Various models and trademarks exist, with names such as Garnier limbs (GLs); tree anchor bolts; artificial limbs; heavy limbs or hyper limbs (HLs); special tree fastener or stud tree fastener (STFs).

They may be either of through fastener style (for smaller trees) or side mount type for larger ones.[1]


One of the main features of TABs is their strength, requiring fewer tree penetrations for robust fastening of a treehouse and hence less damage to a live tree. A typical TAB consists of a threaded metal bolt and a larger diameter collar. The latter provides an extra bending strength by bearing upon the compression strength of the tree grain.[1] Since treehouses are subject to frequent load reversal produced by winds, TABs must be made of spring steel[1] The bolts are able to support from between 9,000 and 12,000 pounds (4,100 and 5,400 kg),[4] a much greater load than conventional lag bolts.

TABs are commonly used in conjunction with pipe brackets, allowing the treehouse structure to move independently with the tree.[2][5][6][7][8] TABs are designed so a tree's added girth can further envelop it.[9][10]


The concept of using a collar or large cylindrical object to increase shear strength in wood construction has been around for several centuries in the forms of split rings and shear plates.[11] Shear plates provide a larger load-carrying capacity in shear than can be otherwise achieved by a bolt alone.[12] Because this idea utilized less bolts for equal strength, it transferred well into the use of live trees, as they compartmentalize more efficiently with a single, larger cut than several, smaller cuts.[13] Michael Garnier became involved in treehouse construction[4][14] beginning in 1990 when he built his first treehouse in Josephine County, Oregon. Two years later, he was ordered by County official to close the treehouse to the public. He began developing what would become the Garnier limb, a high-strength alloy steel engineered bolt that can be screwed into a bore in the trunk of tree. In 1997 Garnier met Arborist Scott D. Baker who shared his knowledge of tree biology and tree structural responses. By 1998, Garnier had developed a commercial bolt product which he called Artificial Limbs. The Garnier limb was primarily developed to satisfy the safety requirements of the Josephine County Building and Safety building permit process.[15][16]

Engineer Charley Greenwood, with the help of Michael Garnier and machinist Michael Birmingham, added a 3-inch (76 mm) collar onto a 1.25-inch (32 mm) hex cap screw to maximize the surface area and minimize compression in the contact area between the tree and the screw.[17] Garnier was initially the sole producer of these bolts under the names, "Artificial Limbs" and "Garnier Limb".[16]

See also


  1. 1.0 1.1 1.2 1.3 """INTRODUCING THE XL SYSTEM ©- FINALLY, A TRUE TREE HOUSE MOUNTING SYSTEM"" (see the link to a brochure)". Retrieved 2013-09-21. 
  2. 2.0 2.1 Van Rheenen, Erin (2010). Moon Living Abroad in Costa Rica. Avalon Travel Publishing. pp. 375. ISBN 9781598808445. 
  3. Globe Pequot, "Knack Treehouses: A Step-by-Step Guide to Designing and Building a Safe and Sound Structure", 2010, ISBN:0762763426, p. 66
  4. 4.0 4.1 Goodnow, Cecilia (23 August 2007). "Northwest Innovators Helped Revolutionize Construction". Seattle Post-Intelligencer. Retrieved 28 December 2013. 
  5. "Interview with Pete Nelson of Animal Planet's "Treehouse Masters"". 
  6. "Pete Nelson – the Treehouse Expert". Animal Planet. Retrieved 28 December 2013. 
  7. "About Treehouse Masters". Animal Planet. Retrieved 28 December 2013. 
  8. Kurutz, Steven (29 May 2013). "Houses for Dreamers (and Kids)". The New York Times. Retrieved 28 December 2013. "Pete Nelson, an owner of TreeHouse Workshop, outside Seattle, is an expert in his field: the design and building of treehouses" 
  9. "Bird's eye brew: Treetop tasting room draws visitors". Akron Beacon Journal. 6 July 2013. 
  10. "How to Build the Ultimate Treehouse". Outside Magazine. October 2013. 
  11. "History of the TAB". Retrieved 2014-02-28. 
  12. "Information regarding shear plates". Retrieved 2014-02-28. 
  13. "Live tree reactions to TABs". Retrieved 2014-02-28. 
  14. Kugel, Seth (26 April 2003). "Refuge among the boughs". Marin Independent Journal. Retrieved 28 December 2013. 
  15. Miskimon, Robert; Chmienlnicki, Steven (2008). The Complete Guide to Building Your Own Tree House: For Parents and Adults Who Are Kids at Heart. Atlantic Publishing Company. pp. 88–89. ISBN 978-1-60138-244-3. Retrieved 29 July 2011. "[Michael Garnier's] battle with Josephine County officials in Oregon began when he built his first tree house, Peacock Perch, in 1990. In May of that year, Garnier sought a building permit from Josephine County Building and Safety to build a tree house, but county officials told him he could not even apply for the license." ...[court battles, national press coverage, testing and development]... "In March 1998, the county accepted Garnier's alternative construction methods and engineering as safe and sound and issued permits for existing tree houses, as well as permits to expand the existing bed-and-breakfast permit." 
  16. 16.0 16.1 Garnier, Michael. "Official Garnier Limb Origin and Histree". Out'n'About Treesort, LLC. Retrieved 28 December 2013. 
  17. "Creation of the TAB". Retrieved 2013-09-21.