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You want to build a tree house and are not sure how big and how heavy it can get? We will show you the basics of tree(house) statics.

Have you already informed yourself about the building permit and know if your trees are suitable? Good, then let’s see how big your tree house can get:

1. Overall weight of the treehouse
2. Position of the platform – well balanced
3. Loading of the individual fasteners – calculation example
4. Load capacity of the tree
5. Summary

A treehouse 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.

1. The total weight of a treehouse

The load of a treehouse is composed of:

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

The loads must be introduced into the platform construction, and transferred to the ground. This is done either directly over the tree and its roots or over an artificial, embedded stilt. The load should be distributed as evenly as possible between the individual attachments.

Also the horizontal wind load plays an important role, because the walls of the treehouse are like a sail. Near the ground, wind speed and lever arm are smaller; the lower the treehouse 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 the load of three different treehouse 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

2. Position of the platform – well balanced

The following example shows a square platform between two trees:

We assume that the platform (without tree house) is loaded evenly & flat. The trees are not in the middle but slightly offset. This results in a certain “load area” (green and grey) for each tree. This is determined graphically: you connect the logs with a straight line (pink line) – then you draw a vertical dividing line at the center – what you see now are the areas that the respective tree has to carry:

  • The total area of the platform is 4 m x 4 m = 16 m²
  • The load area of the left, large tree is approx. 10 m²
  • The from the right, smaller tree approx. 6 m²

This load must now be taken up by a connecting means (e.g. tree bolt) and transferred safely into the tree.

The platform and house should always be positioned so that the more massive tree carries the greater load. The fixed anchor point is set here.

3. Loading of the fasteners – calculation example

With the help of the load areas [m²], the expected load for the respective fasteners can be calculated:

If the area load of the platform alone is e.g. 50 kg/m², the platform alone bears:

the large tree: 10 m² x 50 kg/m² = 500 kg
the smaller: 6 m² x 50 kg/m² = 300 kg

 

Now we calculate the same with a treehouse:

Specifications:
– The tree house stands in the middle of the platform (Type “Habitable treehouse”; 10 m²)

– In it there are 6 funny adults who all drink one liter of beer (70 kg + 1 kg)

– It is winter and a lot of snow falls (100 kg / m²)

 

Here is the formula: 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).

 

Calculation:

– Load tree house [kg] = 10 m² x 125 kg/m² = 1250 kg

– Load remaining platform area [kg] = 6 m² x 50 kg / m² = 300 kg

– Load “funny people” [kg] = 6 x 71 kg = 426 kg

– Snow [kg] = 16m² x 100 kg / m² = 1600 kg

 

Total load [kg] = 1250 kg + 300 kg + 426 kg + 1600 kg = 3576 kg

 

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

Loading on the big tree: (10m² / 16 m²) x 3576 kg = 2235 kg

Resting on the little tree: (6 m² / 16 m²) x 3576 kg = 1341 kg

Now it is important to choose the appropriate fixing method, it is essential to calculate with a safety factor > 2, i.e. instead of 2235 kg, we assume a load of 4470 kg, so our calculations are always on the safe side!

For the big tree I would therefore use 2 x GTS Allstar – more about the load capacity and application range of our treehouse bolts here…

4. Load capacity of the tree

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.

5. Summary

Treehouse 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 “backpack” 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!

Ready for the next steps… read on

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