Frequently Asked Questions - (FAQ)

Supports

How much weight will a beam of x" by y" support?

Please consult your building material supplier for timber strengths for particular spans. For beams that will be supporting the treehouse, the depth should be at least 3 times the width. The depth is much more important for strength than the width.

Should I used fixed or floating/flexible supports?

The only situation where fully fixed supports are recommended is for a treehouse supported by a single trunk. Fixed supports could be used when building between thin branches high in a tree, but building this high could be dangerous due to a lack of support. When the wind blows through a tree, all the branches move independently by different amounts depending on their mass, length and position in the tree relative to the incoming wind. As these movements are unpredictable and incredibly powerful, it is recommended that treehouses supported by more than one trunk/branch use a combination of fixed and floating/flexible joints to the tree.

What types of floating supports are there?

See the supports pages for details of the options.

How will my supports be affected by tree growth over time?

As the supporting bolts are fixed to the heartwood of the tree, and the tree expands by adding layers of growth each year, the bolts will gradually be absorbed into the growing surface of the tree. This effect looks like the bolt is being gradually pulled into the tree, but its position does not actually change. When a beam is bolted directly against a tree, the beam prevents growth where it touches the bark. The bark will appear to bulge around the beam to compensate. This is generally harmless, but will leave a very obvious scar if the treehouse is removed. The swelling can be prevented for a few years by adding a collar between the beam and tree surface made from a piece of metal pipe. The tree will grow around the collar and will not reach the beam for some time, depending on the growth rate of the tree.

When should I consider using ground support?

Ground supports may be used when a certain span between two trunks is too great to be supported by the trees, or where a knee brace extends further than usual from the tree. Before considering using ground supports, consider your reasons for doing so - if the treehouse is so large that the tree can't support it by itself, what measures will you take to ensure the structure is still built in visual proportion to its surroundings?

How should I fix posts in the ground?

Posts should be mounted on a metal bracket fixed into a concrete foundation. The concrete should ideally be positioned below the frost line to avoid cracking in winter. The frost line can be between two and three feet down, so the hole for the post should be narrow and deep. Compress some sharp stones into the bottom of the hole by compacting them with the post, then position the metal bracket and fill in with concrete. Concrete mixes for post fixing are readily available. The remaining space between the top of the concrete and ground level should be filled in with earth so that the ground does not look disturbed. The bracket should be designed to keep the post above ground level. Although it is possible to fix the post directly in concrete, using a bracket removes a lot of contact with moisture and will extend the life of the post considerably.

How do I allow for tree movement with a ground support?

The bracket fixed in concrete could be designed to give some flexibility, either by using a ball joint arrangement or a simple hinged portion to allow movement in one direction. This would absorb side to side motion relative to the ground of the support beam. Ideally, posts should be kept nearer to the fixed joints so that less movement is experienced. If movement at the top of the support is small (1-2") you could get away with having no flexibility at the concrete bracket, because the post itself will allow a small amount of flexibility. This keeps the design simple.