With the weather getting a little frightful as autumn settles in over central New York, work has moved into the shop. Right now, it’s all about walls.

No matter the weather, wall construction moves forward in the shop. Eleven walls for the Ithaca treehouse will be assembled on the ground, then raised in a single day to offer a first glimpse of the treehouse to come.

Perhaps after only the design and construction of a custom treehouse platform, it is the walls that separate the treehouse from other structures for the builder. Although advances in Garnier Limbs have eased some of the trade’s early obsession with weight, treehouse builders are still always mindful of the mass they’re asking the host to handle. Where sound design allows, the structure is lightened. Most treehouses are far smaller than conventional ground structures, and only the rare treehouse sports plumbing and HVAC systems, a kitchen range or a bathtub. That means materials and construction can alter to save weight, while keeping more than adequate strength for the purposes at hand.

While the past decade or so of professional treehouse construction experience has shown weight is not nearly the bogeyman once feared, the same time has made clear that shear and uplift forces – those wind-induced lateral shoves and surprising pickups – are definitely something to be respected. On the ground, one and two story houses generally benefit from their position. Stronger winds tend to be above the ground, where small changes in surface height and dense foliage can’t slow things down. Just think about how many times you hear the wind in the treetops, but feel only a light breeze on your face. Also, with a house sealed to a continuous foundation, there’s no place for the wind to sneak under and try to lift a structure’s metaphoric dress.

With painted trim drying under an autumn sun, future treehouse keepers Colleen and Katie enjoy lunch at pondside.

Put your house 10, 15 or more feet in the air, with it’s slip exposed, and those rules change.

Well designed and built treehouses take this into consideration. Builders, engineers and arborists work together to make sure the foundation and the tree can handle any brief shifts that can come when the wind pushes things around. Although it was typically skipped when the modern treehouse construction movement began in the 1990s, most professional builders now incorporate a plywood sub-layer beneath whatever exterior surface the treehouse will have. Plywood adds a little weight, but it brings with it a wonderful multi-directional strength that reinforces walls and helps them handle even severe shear. Builder and engineer also work to make top rails, blocking, corner posts, and special strapping combine so all those shear and uplift forces are collected neatly and sent back down to that carefully constructed foundation. Good design even takes the roofline into consideration, offering a low edge and gentle rise to the side that sees the biggest blasts of weather. Like the tree itself, treehouses are designed to be light enough to shed stress, but strong enough to resist any force that wants to toss it out of the way

Few things tickle the heart of a builder more than the sight and scent of newly delivered materials. Here, southern yellow pine trim and beveled siding, as well as Douglas fir studs, stand ready to become part of the walls and part of the dream.

Standard 2×4 studs are used in most treehouse walls – bigger than the 2×2s or 2×3s you’ll see in most treehouses built a decade ago – but special attention is paid to the corners and how blocking helps tie them together to work as a unit. In most places, heavy screws are used to attach members rather than standard nails, and those joints are often reinforced with special connecters designed for hurricane and earthquake zones. It’s a little more expensive, but it helps make sure no connections come undone after years of gently rocking in the treetops. That plywood skin will lock it all together, and help the walls remain stiff even though treehouses typically have more windows per foot than most ground houses; after all, you didn’t build in a tree just to be shut out from the view.

All of that trade experience is reflected in the walls. It’s a set of details few would notice, and no one will see once treehouse is finished, but everyone will appreciate for years to come.
And it’s all coming together now in Ithaca.
Once the walls are assembled, and as much siding and trim as possible is attached, the pieces will be raised to the platform and tied together. To most observers, it will look like we built a treehouse in a day. But you and I know, there’s a lot of thought and hard work that go into making things look this easy.