Cabanes als Arbres is a family-owned hotel, located way up in the foothills of the Catalan Pyrenees, near the town of Sant Hilary Sacalm. Up there the mountains are covered with thick forests, especially chestnut and firs, and inhabited by wild boar. From the ridges and high places, you can look out over green valleys far below, and to the north the well-known mountain Montseny is always visible, among the dark peaks of the Pyrenees.
In 2010, I had the
privilege of working on a team of 4 carpenters up there in the
mountains, building ecological treehouses for Cabanes als Arbres.
Each treehouse was designed to be a single large hotel room, complete
with king sized bed, wash basin, compost toilet, couches, table and
chairs, and a large balcony with a great mountain view.
When building a treehouse,
the tree you choose is very important. This is the foundation of the
house. If you choose a weak tree, and it blows around in the wind,
the treehouse becomes like a boat in the sea, rocking about and
upsetting the inhabitants. We would carefully select our trees to
ensure we would have a strong, straight base for the treehouse –
and an excellent view, of course!
The way that the tree and
the house interact is also very important. Two big topics to think
about are: how is the frame of the treehouse connected to the tree,
and how is the roofline interacting with the tree.
When framing the
treehouse, you need to allow the tree some space to grow. By framing
tight up against the trunk, you're going to create a conflict between
the treehouse and the tree – and one of them is going to get
damaged. A good couple of inches needs to be left between the frame
and the trunk.
The next step is attaching
the frame to the trunk. The life of the tree is focused in the
outermost layer of the trunk, so even small, superficial punctures
into the trunk are going to affect the tree, causing its sap to flow
out. Instead of causing many small punctures, the key to a good
connection is to use a minimal number of large bolts, bored straight
through the unliving wood in the center of the trunk. In the next
photos, you can see the large galvanized brackets that are mounted in
the center of the treehouse's frame. These brackets are connected
with a single large bolt that passes through the trunk of the tree.
This hole was sealed with silicone to prevent the tree from dripping
out its sap while it healed afterwards. A second large bolt passes
through the tree above the treehouse, and four cables connect this
bolt to the four principle corners of the frame. These two holes are
the only holes we put in the tree.
The other major
consideration is how the roof interacts with the tree. There needs to
be a space so that the tree can grow, and also to allow the tree to
bend in the wind. Treehouses that are built with the roof framed
tight against the tree can be heard complaining constantly through
windstorms, as the frame shudders and pops under the strain of the
moving tree. But on the other hand, if a space is left against the
tree, then rain can come right in. At Cabanes als Arbres, we handled
this part of the design with two features: first, the tree passes
through the peak of the roof, so that the roofline is always sloping
away from the tree. Second, a space is left around the trunk while
building the roof, and afterwards a small tent of wood or canvas was
erected, tight against the tree. The tent would shed rainwater while
still allowing the trunk room for movement.
The ceiling and walls were
insulated with batts of wood fiber, an environmentally friendly
wood-based insulation alternative. Then the floor, ceiling and walls
were finished with pine tongue and groove. We added built-in features
like the dry compost toilet, shelves, wash basin, and banister. The
windows and ladders were made for us by a nearby craftsman.
Bridges and staircases
were fun extras, too. We would always be excited when we found a tree
that we could build a nice long bridge for!
Working at Cabanes als Arbres was a real pleasure for me. The design and building of
treehouses is a true art, and it's not very common to find a forest
that's home to so many impressive specimens. From the high level of
detail in the plans, to the selection of all-natural, high-quality
building materials, the treehouses at Cabanes als Arbres were
probably as much fun to build as they are fun to stay in.
- Ben
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