Scott Baker, owner of Tree Solutions and Villa’s arborist of many years, is helping us work with the city on construction approval. Below is an excerpt of a letter he wrote to the City Department of Construction and Inspections.
“..In recent history, there has been an increase in the construction of treehouses and other tree‐supported structures throughout the world. Numerous treehouses have been built that have met building codes in jurisdictions all over North America, many of which I am familiar with or have participated in planning.
Locally, I have monitored treehouses built in Douglas‐fir trees (the same tree species that would be used at Villa Academy) and can report that after 20 years, the trees in these instances are doing well. Additionally, there is a treehouse at a private camp on Orcas Island that has been in continuous use for more than 60 years. I believe that using current methods, a treehouse at Villa Academy can be constructed to last as long as a typical building can, without compromising the health of the trees that support them.
I have been advising clients regarding construction near valuable trees for more than 20 years and have taught tree biology and tree biomechanics to attendees at the World Treehouse Conference since the first such conference in 1996. Since then, Tree Solutions Inc. has also served a growing number of clients who are using trees as structural supports for treehouses, ziplines, and ropes courses. With my involvement, the City can have confidence in allowing such a structure to be built…”
More technical excerpts of Scott Baker’s letter:
“The project planning group had a pre‐planning meeting with city staff on October 13, 2016. At that meeting we explained our idea and floated the idea of using trees to support the structure. Our idea was well received by the various city building officials with one exception: the Senior Environmental Analyst told us that the structure would have to abide by the Seattle’s Directors Rule 16‐2008 which regulates exceptional trees and groups of trees (groves).
The area where the Villa Treehouse would be built is within a grove of trees and the two support trees would be Douglas‐fir (Pseudotsuga menziesii) trees which are both exceptional by size.The Director’s rule states that construction within the dripline of an exceptional tree may be allowed if “limited toone‐third of the area within the outer half of the area within the dripline” (defined as the horizontal area equal to the maximum extent of all branches and leaves) with a plan prepared by a Tree Care Professional.
This requirement was designed considering the major impacts of traditional construction practices on trees, which often require continuous foundations that penetrate the soil layers where tree roots exist. If a structure does not cut into the soil, then the impact to the tree roots is minimal. This brings us to a dilemma as we want to connect the trees within their inner root zone. While our project would be built within the drip line, we will not require continuous footings, therefore only minimal disturbance to treeroots will occur and impacts to nearby trees will be minor.
The trees that are being considered for use as supports at Villa are both large young Douglas‐fir.Douglas‐fir is an ideal species for this use because of their decay resistance and long life span. The structure would partially be supported by the trees. There would be two penetrations on each tree house with attachment bolts (TABs). TABs minimally impact a trees’ vascular transport system. The site is sloped, which will allow other parts of the structure to be built on a foundation at the edge of the dripline, but in contact with the ground. Currently the project is considering several foundation systems—all of which will involve minimal disturbance to the tree root zones.”