Although by definition, a treehouse is a structure built in trees, it is quite possible to build one without the benefit of strategically placed trees. Aboriginal people from many parts of the world took up residence in trees to escape predators, defend themselves against other human enemies, and to avoid wet or damp conditions on the ground, especially in the tropics.
For some of these people, the natural next progression was to build elevated houses or platforms on poles they implanted into the ground themselves, and with this method, anyone can build a treehouse, even on a treeless prairie or a featureless suburban backyard.
The first step is to determine the size and number of the poles you need to support the treehouse. This is dependant upon the intended use of the structure. Many small treehouses are simply used for a child’s playhouse or fort and can be built with minimum materials and lightweight support poles. Larger treehouses might be used for such things as a writer’s retreat, weekend camp house, or even a permanent residence.
Support poles should be of pressure-treated lumber for long-lasting durability. The smallest ones available are 4×4 inches square and these are perfectly adequate for small playhouses less than 10 feet off the ground. Larger sizes can be used to support heavier structures. They are available in 6×6, 8×8, and even 12×12 inches square. Round poles like those used by utility companies are also available and can be used to build entire houses high off the ground. For our purposes here, we will focus on the 4×4 size post and the construction of a small child’s treehouse.
Pole or post-supported treehouses can be just as sturdy as those built-in live trees and might last even longer, as live trees often die when nails or other fasteners are driven into them. The key to strength is to set the poles in the ground at an adequate depth so that they become immovable. For this step, you will need a manual posthole digger, or you can rent a power auger from a tool rental company.
Post holes should be dug to a minimum of 2 feet and even deeper in northern climates where the frost penetrates deep into the ground. Many people have the mistaken notion that posts or poles should be set in the post holes using the concrete mix to fill the holes up to the surface level. This is a bad idea because rainwater collects on top of the concrete and causes premature rotting of the post, which can cause it to eventually break off right at the surface level. For adequate drainage, it is much better to fill the hole with the earth removed while digging it, or with pea gravel.
This can be tamped firmly with the end of a shovel as it is filled in; resulting in a rock-solid post, assuming the hole was deep enough in the first place. If you are worried about the posts settling deeper after the weight of the treehouse is added, it is better to place solid concrete blocks at the bottom of the holes for the posts to rest on than to fill the holes with mixed concrete. These footer blocks are usually not necessary, however, unless you are building on particularly soft or unstable land.
The 4×4 posts should be placed so that they are no farther than about six feet apart. This way the span of the structural beams supporting your treehouse platform will not be under excessive strain, and a larger number of poles will provide a better anchor to the earth in the event of high winds that could threaten to topple the entire structure.
Once the posts are set, join them with connecting beams of at least 2×6 inches for the lightest structures or 2×8 to 2×10 for larger treehouses. These beams form the perimeter of the platform, and between the beams, you will need to install floor joists on 2-foot centers to serve as framing for the floor platform.
Construction of such an elevated platform is exactly like building a deck on the ground. Once the platform is framed and the floor planking installed, you may then build walls and a roof if desired, or a simple safety railing if the treehouse will be just an open platform. Access to the platform can be gained by building an elaborate staircase, a straight wooden ladder, or for even more fun, a rope ladder.
Building a treehouse without trees is a fun and relatively easy project, so if you want a treehouse for those times you need to get away from the ground, don’t let the absence of a grand old oak tree in the backyard deter you.Building a treehouse