It is difficult to find someone who has never dreamed of building or having a tree house to call their own. The idea of a refuge, a space fully integrated with nature and with a privileged view, pleases almost all ages. There are examples of tree houses of all scales and complexities, from small elevated platforms to highly complex structures, including electrical and hydraulic installations. Some sites specializing in the topic (yes, that exists!), offer valuable tips for building these dreams. In general, they subscribe to the motto: "Choose your tree, make your project, but be ready to adapt it!"
This approach is essential because - unlike what we have seen in the industrialization of civil construction and in the evolution of BuildTech technology in architecture, where all stages and processes are predictable and controlled - when working with a living being, which moves, grows, and adapts, many certainties cease to be certain. Although there are no strict laws or rules for this, when building a safe and resistant tree house, some important considerations must thus be taken into account.
The tree to be used should be considered carefully. First of all, you should check that it is healthy, has no apparent illness, is well rooted, and, preferably, that it has already reached its peak growth. These checks are vital, as this tree will be the foundation and the backbone of your home. There are several variables and possibilities to take into account. You can use a single thick trunk, several branches of the same tree, or even trunks of nearby trees. This choice will influence the possibilities for dimensions of the structure, as well as considerations of spans and balances, which can lighten or increase the load placed on the trees. For example, when fixing the structure to two different trees, it should be considered that each tree may have different wood densities and react differently to the wind.
Every time we move, we drill, or we strip the trees, these actions are an aggression and a source of stress. Therefore, one should try to keep this to a minimum. Drilling fewer, thicker holes is less harmful than drilling several smaller holes. Always avoiding drilling holes at a distance of less than 30 centimeters from each other. To fasten to the tree, use screws, never nails, and ensure that they are at least 20 cm long to allow a lot of adhesion. Retention screws (which do not go through the entire tree) are best to prevent damage to the opposite side of the trunk.
It is important to point out that trees have a particular healing process, for which the technical term is compartmentalization of decay. Trees are not able to replace or heal, but instead, they try to "seal" damaged tissue outside healthy tissue. When injured, the thick-walled cells of the wood are isolated from the adjacent cells by chemical substances resistant to rot, such as phenols and turpentine. These same substances are extracted and used as raw materials for products for the protection and finishing of wooden parts.
But to return to the tree houses, possibly the most critical issue when building them is structuring the floor slab, which is what facilitates the development of the rest of the building. For this step there are several possibilities, with different variables leading to diversified solutions. Perhaps the best source for venturing into building tree houses is The TreeHouse Guide, which encompasses most of the possibilities and potential problems to be encountered in a construction like this.
If you only have one trunk at your disposal, your focus will obviously have to be on it. But it is vital that the beams have some type of reinforcement, such as diagonal brackets or even auxiliary pillars to the ground, so as not to overload the connections.
If there are multiple branches or trunks that are not sufficiently thick, one possible solution is to create a fixed frame between them. This method is the simplest way to build, and does not require great structural or carpentry knowledge. Best practice is to be careful and attentive in the construction, using large gauge pieces with special care for the joints between them. As our main source explains, if the branches are not very large or heavy, the small tensions produced by wind can be resolved by these supports. The complete floor structure will need to be rigidly attached with strong fixings (nails or large screws) so that the stresses do not break the joints. This method is not suitable for large spans or for use between thick logs.
When the design calls for a structure with larger spans, across multiple larger trees, flexible structures must be considered. This flexibility is necessary because, considering that the structure will be attached to different tree types, the supporting trees will each behave differently in, for example, a windstorm, which can twist the structure of the house in such a way as to break its connections, causing the structure to collapse. This flexibility allows for the use of thinner and cheaper parts, but also makes the structure more complicated to build. One end of a beam must be attached to the strongest trunk and the other end, supported by a sliding joint. This is the moment that we architects must remember those dreaded classes in structures involving first-order bonds (as in this case) and second-order sockets and bonds. The structure is only supported and secured at one end, whereas the beam is free to slide when the tree moves with the wind.
Another method, a little more complex, is to take advantage of traction, using steel cables. A steel cable is attached at one end to the support and to a higher branch at the other end. This method is cheap and effective, but you need to be very careful that the tree does not come into contact with the mobile cable. Steel cables have enormous tensile strength and can give the impression that your home is floating in the trees. This link provides more information with which it is possible to better understand this system.
After the platform is built, the walls and roofs can be constructed. Preferably, architects should avoid materials that are too heavy, since most of the load will continue to be absorbed by the respective trees. Over time, once built, observing whether the connections remain firm and whether the structure remains level is essential to prevent the house from breaking and hurting someone. Of course, a tree house is not the safest place to be in the event of a strong wind and it is definitely not a good place to be in a lightning storm. It is also important to point out that there are some areas that require authorization from government bodies to build a structure like this, even on your own land.
These tips are not meant to discourage you from building your dream tree house. As the ARUP engineer points out in this video published a few years ago, perhaps the most important tip is to follow your own intuition and to observe the capabilities of the tree on which you build. Experimentation and observation are very important factors when designing and building structures of this type. And, of course, perhaps the most important thing is to have fun in the process!