Lesezeit: 4 min
You want to build a tree house and are not sure how big and how heavy it can get? Here you will find the most important basics of tree (house) statics.

Structure:

  1. Weight of the tree house – area load per m²
  2. Position of the platform – Load intake surfaces
  3. Loading of the individual fasteners – calculation example
  4. Load capacity of the tree
  5. Summary

A tree house for a tree is like a big backpack for a person – health, stature and environment determine how big and how heavy the backpack may be so that the person can still move freely. If you carry the backpack for a while, your body gets used to its weight and builds up muscles in a targeted manner – the same applies to a tree.

In the following article we show you:

  • A simple method to estimate the weight of your tree house.
  • In order to find out the load of the individual fasteners.

The load of a tree house is composed of:

  • own weight (wood, roofing, windows, furniture, etc.)
  • Traffic load (crowds of people)
  • Natural stresses (snow, rain, storm)

All loads must be total in the beam construction introduced, and transferred to the ground. This is done either directly over the tree and its roots or over an artificial, embedded support. The load should be distributed as evenly as possible between the individual connecting means and girders.

Also the horizontal wind load plays an important role, because the walls of the tree house look like a sail. Near the ground, wind speed and lever arm are smaller; the lower the tree house is fixed in the tree, the larger it can be dimensioned. So that the tree does not experience any rotation, the house should be built as evenly as possible around the trunk .

Special attention should be paid to the snow load in alpine regions, this is sometimes set at over 500 kg/m²! Platform size and roof pitch should be adjusted accordingly.

Orientation values for Eigenlast of three different tree house types can be found in the following table; the values include substructure, platform, railing and house:

Tree house type Facilities Load [kg/m²]
Simple children’s playhouse; < 15 m² incl. terrace non-insulated, very lightweight construction ca. 60 kg/m²
Living tree house; 15 – 25 m² incl. terrace Stable construction, slightly insulated, high-quality roof covering, glass windows approx. 125 kg/m²
Luxury tree house; 15 – 40 m² incl. terrace Massive construction, thick wall construction, excellent insulation, sanitary facilities, triple glazing approx. 155 kg/m²

The following example shows a platform between two trees. If the platform is loaded evenly over its entire surface, a certain “load absorption area” results for each tree (see sketch). This is determined graphically by drawing a vertical straight line in the middle between the two tree axes:

  • The total area of the platform is 2.5 m x 4.0 m = 10 m².
  • The load intake area of the left, large tree is approx. 2.3 m x 2.5 m = 5.75 m².
  • From the right, smaller tree approx. 1,7 m x 2,5 m = 4,25 m²

The platform and the house should be positioned so that the more massive tree carries the greater load.

The load absorption areas [m²] can be used to calculate the expected load for the respective fixing point: Load [kg] = area [m²] x area load [kg/m²] + other loads [kg] ; the area load is the sum of the individual loads (dead load + traffic load + other loads).

As an example we calculate the load of the above platform for the tree house type “Normal” (10 m² + max 6 persons a 70 kg):

Load [kg] = (2,5 m x 4,0 m) x (125 kg/m²) + (6 x 70kg) = 1670 kg

Now we calculate the same house with additional 200 kg/m² snow load (wet snow):

Load [kg] = (2,5 m x 4,0 m) x (125 kg/m² + 200 kg/m²) + (6 x 70kg) = 3670 kg

From this, the load of the individual trees can be calculated with the help of the catchment areas:

Loads on the large tree (5.75 m² / 10 m²) x 3670 kg = 2110 kg

Loads on the small tree (4.25 m² / 10 m²) x 3670 kg = 1560 kg

Now it is to choose the suitable fastening method, you should calculate with safety factor > 2, i.e. Statt 2110 kg, we assume a load of 4220 kg, so our calculations are always on the safe side!

For the big tree I would therefore use 2 x GTS Allstar – More information about the load-bearing capacity and application range of our Tree house screws here

Trees can carry incredible loads!

To get a feeling: Wood has an average compressive strength along the fibre of approx. 2 kN/cm², converted 200 kg/cm². A round, straight growing tree trunk, diameter 40 cm, can theoretically carry a load of 1256 cm² x 200 kg = 251.2 tons.

The possible load of a tree house results from the maximum load-bearing capacity of the individual fasteners, which is 1000 – 5000 kg depending on the fastener (more detailed information on the individual fasteners here).

We always recommend to work with a safety factor > 2; this includes possible defects in the wood as well as exceptional conditions such as gusts of wind, heavy snowfalls or accumulations of people. In other words, even if the screw can theoretically hold 4 tons, it should only be loaded with 2 tons.

Tree house construction is lightweight construction – Avoid heavy materials such as stone slabs, huge windows with triple glazing, hardwoods, steel sculptures, dairy cows, …

Think about exactly where which loads arise and how to distribute them most cleverly on the individual fasteners.

Choose the “rucksack” one size smaller; you can still extend the tree house at a later date if necessary.

The house should be adapted to the tree and merge with it instead of “crushing” it.
The overall picture should always be harmonious!

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