Frequently Asked Questions (FAQ)

Trees

What is a good tree to build in?

Almost any mature, healthy deciduous or coniferous tree can be used to support a treehouse. Examples of particularly good species include; oak, beech, maple, ash, cedar, hemlock and Douglas-fir. If building in a very windy site, see the question below about strong winds.

How big does the tree have to be?

This depends on the size of the treehouse and its position in the tree. For an average sized treehouse of 8'x8' a trunk diameter of 12" or more is recommended if using a single tree. If supported over two or more trees, smaller minimum diameters will be suitable. The design of the treehouse may make it heavier than usual, in which case a larger diameter will be required, or a tougher species. Deciduous trees tend to have denser wood which can support greater loads.

How can I measure the diameter of the tree?

Work out a circumference by wrapping a string around the tree where you intend to build the supports and measure the length with a tape measure. Assuming the trunk is roughly circular, divide this measurement by pi (3.142) to find the diameter.

How can I tell how old my tree is?

The easiest way to measure tree age is to cut it down and count the number of rings, but of course this is not practical for the treehouse builder. A core can be taken by an aborist or tree surgeon in order to count the rings without killing the tree, although they can usually give you a rough idea from the size and appearance of the tree. For the purposes of treehouse building it is not important to know the age of the tree - the physical size is much more useful in determining strength.

How can I tell if my tree is healthy?

Basic signs that might indicate ill health include several dead branches near to each other, patchy leaves on branch extremities, leaf discolouration, and liquid oozing from the bark. You should consult an arborist/tree surgeon to check your treehouse is healthy if you are in any doubt. Building work near a tree can damage the root structure by breaking/damaging parts of the root network, and compacting the earth (which reduces drainage and air permeability). Regrading of the land around a tree can be particularly damaging as the roots that were previously near the surface are starved of oxygen and the soil may be compacted, reducing drainage. Symptoms of damage caused to the roots may take several years to become visible.

Do nails, screws, bolts, ropes or cables damage the tree?

The use of nails, screws or bolts can cause health problems for a tree if not fitted correctly. Cables and ropes slung over branches are very damaging, as they cut through the bark as the structure moves. Any damage to the bark of the tree, whether by nail, screw or bolt, is a potential entry point for infections and bacteria, so it makes sense to keep the overall number to a minimum. Multiple punctures can cause dangerous compartmentalisation.

The general recommendation for fixing supports is to use a single, large bolt fitted into a cleanly drilled pilot hole. Nails and screws are not strong enough for major supports without causing tree damage. For more detailed information on how trees can be damaged by treehouses and how to reduce the problems, see the tree damage page.

Can I bolt all the way through the tree?

Yes, but this is not necessary. Large lag bolts are widely available which are suitable for supporting treehouse beams with only one puncture point in the tree. Drilling through the trunk also requires very long drill bits.

Will the treehouse get higher over time as the tree grows?

No. Trees grow larger by expanding their diameter and growing new branch tips, not by stretching the entire tree. New layers of wood are added during the spring and summer which increase the diameter of trunks and branches. The only part of the tree to get any higher are new shoots, which extend from the ends of branches. Once one season has passed, these shoots will not grow further, but will expand as branches and the trunk do. The following season new shoots will extend from the end of the previous season's growth. As a tree matures, most species lose their lower branches as they become shaded by the foliage above, leaving a bare trunk. This can give the impression the branches have been lifted higher, when the higher branches are in fact new. As a treehouse is fixed to the heartwood of the tree it will remain at a fixed height from the ground over time.

How will the treehouse affect the tree in strong winds?

A treehouse will act as a sail in strong winds, which can add a large load to the tree's roots. Trees normally withstand excessive wind speeds by shedding parts of their structure, first leaves, then small branches, then large branches. This means that the area that catches the wind and could potentially push the tree over is limited to the large branches and trunk, as smaller parts will be blown off before wind speeds are high enough to push the tree over. A treehouse can therefore present a considerable extra wind catchment area. A tree in a forest will experience much lower wind speeds than one in the open. A treehouse low in the tree will experience lower wind speeds and will produce lower forces on the roots because the leverage effect of the trunk will be less. A treehouse with open walls that allow air through will cause much lower sail effects. A tree will react to the presence of a treehouse within a few years by adding extra thickness to supporting roots. This means the tree is most vulnerable during large storms in the first few years after a treehouse is built, but will subsequently be more able to cope.