Trees

Basic Information

In order to build a treehouse you have to be able to judge the trees. There are several factors that influence whether a tree is suitable for building. These factors are the same for both trees and conifers.

A healthy, intact tree is able to absorb the forces that are caused through building a treehouse. Healthy trees are in balance. If an injury or imbalance occurs somewhere, the tree immediately tries to compensate for the mechanical or physiological damage by targeted growth. With such a scar, the structural integrity is compromised; the degree to which the tree is compromised is difficult to judge, making this tree unsuitable to build upon.

Further Information

The Tree Body Check: How to Select Trees

We can only build tree houses on healthy trees. Therefore it is important to assess the health of every single tree by means of a small body check. Check the tree from head to toe ...to root:

What does the tree crown look like? Does the tree have healthy, dense foliage?
Are there large dead branches? Be careful, these can fall down!
What is the relationship between tree height and trunk thickness?
Is the trunk straight? How are the tree forks?
Does the trunk have fungal infestation? Are there large areas of dead bark? Other visible injuries?
How is the trunk rooted?

The method described here to estimate a tree is very rudimentary. For a more in-depth assessment, which goes beyond our treehouse building method, trained arborists are needed.

Further Criteria for Checking Trees

h/d Value

The stability of a tree can be estimated by the ratio of tree height (h) to trunk diameter (d), the so-called h/d-value. The trunk diameter is estimated at about chest height. The lower the value, the higher the safety reserves. If the h/d value is greater than 50, the trunk may fail (e.g. buckling). To be on the safe side, we recommend the following values:

maximum fixed point height with - radial force application	maximum fixed point height with - axial/ diagonal force application
h/d = maximal 20 - 25	h/d = maximal 25 -30

These values are only valid if the diameter of the trunk at breast height is at least 20 cm.
The limits apply only to trees that are judged to be otherwise sufficient in their overall appearance

Leaves

All tree species have two important functions: photosynthesis (i.e. the exchange of oxygen and Co2) and the release of moisture into the air. It is important to note that even a beautiful green tree can be dangerous! Just looking at the leaves to see if a tree is suitable for a tree house is not enough. However, a significantly reduced foliage with many dead leaves in summer is almost always an indication that a tree is not healthy. To be clear, coniferous trees also called considered to have leaves (needles).

Roots

The tree roots take in food and water and transport them up to its uppermost leaves. The roots are the foundation of the tree - therefore they are crucial for its stability. Damaged roots, roots raised from the ground, or changes in soil level (e.g. at an edge) are indications that a tree may be insufficiently rooted. Roots are thickest where the load is greatest. On the windward side, trees often have their thickest and longest roots.

Are there concentric and gaping cracks in the bark near the stem? The wind has probably pulled the tree quite hard and the anchoring in the ground is no longer the best then. Be careful with trees that stand directly on riverbanks. The root system has often been washed out and has therefore lost stability.

Growth and Form

Crooked Trees

Crooked trees and branches without top shoot straighten up.

Crooked trunk and crown: tree stands crooked.	Crooked stem but straight crown: tree once stood crooked.
Danger of falling! Absolute exclusion from use.	It has stabilized itself. The further down the kink is, the longer ago it happened.

Trees in wind-exposed areas straighten themselves.

Tree Forks

The thick branch brings a heavy weight load into the trunk, which is therefore thicker underneath than above the branch. The tension is evenly distributed on the surface of the tree.

U-Fork: stable form which can be loaded in all directions - even above.
V- Fork: susceptible pressure spike. Can tear further. Often seen in beech trees. Fixed points above are problematic.

Injuries and Defects

Cavities/ Rotten Spots

If a tree has large cavities or decaying places, this means that its carrying capacity is limited and the tree is not suitable to be used in a treehouse. Wood infested by insects and fungi quickly loses its load-bearing capacity.

Animal Housings

Signs of dwellings of larger animals (e.g. birds etc.) are indications that the trunk has major internal damage.

Condition of the Bark

Larger injuries in the bark, cracks and bulges are signs that the tree was injured in that area - similar to scars on human skin. Large dead parts of the bark are an indication that the tree is in a poor health condition.