As motor skills sharpen, children become fascinated with climbing trees. Trees with low-hanging branches are ideal for tree houses, offering children a safe way to play in the trees. Building a tree house encourages children to prolong the time they spend outdoors and be creative by providing them with a private play space. Unfortunately, trees can be damaged and sustain long-term injuries if you use nails or screws to attach a tree house to a tree. A few options are available which allow you to fasten a tree house to a tree without causing any damage with nails.
Start with the base using tongue-and-groove floorboards or exterior plywood. Build it to sit on the main branches, centered around the trunk. Distribute weight evenly across all the branches it is resting on. Anywhere the tree will come through the base, leave space for trunk growth. Do not use the trunk to attach the tree house, as the main stem is not disposable like branches and damage to it must be minimal. Leave the area in the floor or walls where the trunk comes through alone.
Rather than wedging planks between branches, attach eye-bolts on the outside of the floor near any limbs. Wrap rope around the branches at least four times and then through the eye-bolts, knotting securely. Use a minimum of two eye-bolts under the floor to keep the base of the tree house firmly attached.
Use wood that is at least 1/2 inch thick for the walls and roof. Keep windows small and use flexible materials for rather than glass. Place the door where it is not blocked by branches and can be accessed by a ladder. Fit it snugly into its frame and make sure it closes securely so that it does not open if leaned on.
Attach eye-bolts to the wood of the walls near any branches. Use one eye bolt for each branch and at least one for each wall. Wrap rope around the branch four times and then through the eye-bolts, knotting tightly. Tie up the rope's loose ends or melt them into knots. Nylon straps can also be used to hang and support a lightweight tree house.
Another option is a method Tadashi Kawamata used for securing a tree house without nails on tree huts built in Madison Square Park in New York City. This system consisted of wrapping rubber sheath around branches and using ratcheting straps to fasten the branches to the lumber. The technique protects the bark and keeps it from being scraped or worn.