**How big and heavy can my treehouse be?**

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

In the following article, we will dive a deeper into the topic of **supporting structure and statics**. This is important if you plan a **public project** or if your treehouse is going to be **very large compared to the tree**.

In order for this article to help you, **you should already have a rough idea of:**

- The tree you want to build your treehouse in
- Overall size and orientation of your platform
- The total size of your treehouse (m²)
- The different mounting options

Our goal here:

We want to know how much load is on our individual treehouse anchors so we can size them correctly.

**Learn from the Treehouse Professional:**

**Rule of thumb for calculating the total weight of treehouse****Important basic rules for load distribution****Load distribution – find the perfect position of platform and house****Loading of the individual fasteners****Load capacity of the tree – will my tree hold?****Summary**

### Introduction – How a tree deals with a house:

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: it will feel the treehouse and form extra strong wood in the important places.

Properly dimensioned,** the tree and your treehouse will form a lifelong symbiosis!**

**1. Rule of thumb for calculating the total weight of a treehouse**

**The load / weight of your tree house is made up of:**

### Dead load

The **sum of all fixed, static parts** of your house: *wooden beams, boards, roofing, windows, furniture, screws, … *

### Live load

The **sum of all moving parts**: People & animals. **Consider the following scenario**: at a party, all your friends go up to the tree house and all pose on one side for a photo…. “and on the count of 3, please all jump!” **That’s live load – that’s what your tree house has to withstand 😉**

### Wind load

The walls of your tree house act **like a sail**. The higher your house is in the tree, the stronger the wind load becomes, and at the same time the larger the lever arm becomes – **so the higher your house is in the tree, the smaller it should be!**

The tree and the fasteners do not like torsion: To avoid twisting movements, build your tree house **as evenly as possible** on the trunk.

### Snow load

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

**All these loads** must be absorbed by your **platform construction** and transferred into the ground. This is done either directly via the tree and its roots, or via an artificial support set in concrete.

The load should be **distributed as evenly as possible** over the **individual fasteners.**

**Here you will find orientation values for the dead load of three different treehouse types**

#### (the values include the substructure, platform, railing and house):

##### Simple children's playhouse

(< 15 m² incl. terrace)

##### Type of construction

- Very lightweight construction

##### Surface load

[kg / m²]

##### Habitable treehouse

(10 - 25 m² incl. terrace)

##### Type of construction

- Lightly insulated

- Valuable roofing

- Glass windows.

##### Surface load

[kg / m²]

##### Luxury treehouse

(15 - 40 m² incl. terrace)

##### Type of construction

- Thick wall construction

- Excellent insulation

- Plumbing

- Heavy windows.

##### Surface load

[kg / m²]

**The dead load** of an “inhabitable tree house” with 10 m² therefore is approximately:

10 m² x 125 kg/m² = 1250 kg

**2. Important basic rules for load distribution**

**Important basic rules for a project in several trees:**

- The
**most massive, thickest tree is the fixed point**(e.g. with “Static Support”), as this moves the least. - In general, the
**larger trees should carry more load**– larger trees sway less and can take more fixings (e.g. multiple bolts).

**Exception rule – ****hardwood vs softwood:**

Note that it is not primarily the trunk diameter that is decisive when taking up loads, **but the load capacity of the individual fasteners! This is approx. twice as high for tree screws in hardwood as in softwood!**

Here is an example to explain:We build a treehouse between two trees:

- Beech: diameter ø 50 cm
- Spruce: diameter ø 70 cm
We use 2 x of our Tree Screw

GTS Allstarfor fastening; this bears approx. 4 tons in beech wood, only 2 tons in spruce wood.

Consequently, the “smaller” beech can carry 8 tons of load, the “larger” spruce should carry a maximum of 4 tons.

**3. Load distribution – find the perfect position of platform and house**

Using a classic **2-tree treehouse** as an example, we show you **how to calculate your loads step by step** and then choose the **perfect fixing method.**

**Step 1: The setting**

We assume that you have already thought about your tree house, that you have **mapped your trees**, and already have a **rough idea of the orientation of your platform.**

**In our example it looks like this:**

Two spruce **trees ø 40 and ø 60 cm**; and a **square platform of 4 x 4 m** which slightly **overhangs** to the right.

We now want to check **how much weight is acting on the individual trees.**

**Step 2: Find the centre line**

The centre line is the dividing line of the load bearing surfaces. It shows us what proportion of the area of the platform acts on which tree; this **is determined graphically:**

- connect the tree trunks with a straight line
- draw the centre line of this line (
**yellow line**: at the centre a perpendicular dividing line) - what you see now are the areas that the respective tree has to bear…

**Step 3: Load bearing areas in m²**

- The total area of the platform is 4 m x 4 m =
**16 m².** - The load bearing area of the
**small tree on the left is approx. 6 m².** - The load bearing area of the
**large tree on the right is approx. 10 m².**

**Step 4: Place the tree house on the platform**

Now we position our house on the platform – in this example, for simplicity’s sake, centrally.

**Here it becomes obvious:**

- if the house would be in the
**green zone**, the “small tree” would have to take the load; - if the house were in the
**orange zone**, the “big tree” would bear its load.

**Step 5: Calculate the maximum total load**

Now we calculate the expected maximum load of our treehouse with the help of **our rules of thumb.**

This extreme peak load probably only occurs every few years – but then the tree house construction must withstand!!!

**Details:**

**Total area = 16 m²**- The tree house stands in the middle of the platform (type “habitable tree house”; 10 m²) = dead load
- There are 6 funny adults inside, all drinking a litre of beer (70 kg + 1 kg) = live load
- It is winter and there is a lot of snow (100 kg/m²) = snow load

**Calculation:**

**This 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 + live load + other loads).

**Dead load tree house [kg]**= 10 m² x 125 kg/m² =**1250 kg****Dead load remaining platform area [kg]**= 6 m² x 30 kg/m² =**180 kg****Live load “Funny People” [kg]**= 6 x 71 kg =**426 kg****Snow [kg]**= 16m² x 100 kg/m² =**1600 kg**

Total load [kg] = 1250 kg + 180 kg + 426 kg + 1600 kg = 3456 kg

**Step 6: Load distribution on the trees**

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

The load on the large tree is: (10m² / 16 m²) x 3456 kg = 2160 kg

The load on the small tree is (6 m² / 16 m²) x 3456 kg = 1296 kg

**The SAFETY FACTOR (SF >2)!!!**

Now it is necessary to choose the** appropriate fastening method.**

It is essential to calculate with the **safety factor > 2**, i.e.:

Instead of 2160 kg, we assume e.g. 4320 kg load, thus our calculations are always on the safe side. Then even hurricanes, earthquakes and tsunamis will not harm your treehouse!

**4. Loading and choice of suitable tree attachments**

**Now it is a matter of choosing from the various fastening methods the one that supports your platform most securely. Often there are several good solutions and combinations.**

**The “GTS Allstar” is perfectly suited for our example project, the maximum load for one bolt is:**

1080 kg x SF2 = max. 2160 kg / screw

In spruce (softwood) the screw carries about 2 tons, **in combination the screws stiffen**, so with two screws you should be able to safely carry 5 tons load per tree.

**Now we will show you two variants for anchoring the supporting structure with our GTS Allstar:**

**Variant 1: Parallel support beams**

**Analysis:** This construction is a real classic! However, the whole thing **would be a bit wobbly** here, as:

- the platform protrudes far to the side
- the house is relatively large and protrudes sideways

If, for example, all 6 beer friends were to pose for a photo in the bottom right corner, the** platform would start to wobble.** The construction would certainly hold, but** too much wobbling gives an uneasy feeling and in the long run strains the fasteners!**

#### Another disadvantage:

With a **diameter ø 40 cm** (small tree), **two opposing GTS Allstars are very tight.**

If the diameter is somewhat smaller at this point, e.g. because the trunk is oval instead of round, the tubes could touch each other in the middle – that would be a big bummer!

**Variant 2: Triangle construction with V-bracket**

**Analysis:** A **triangular construction** is the perfect solution here!

The bolts lie neatly under each other, which means that even a smaller trunk diameter does not matter.

Thanks to the **V-bracket**, the triangles can open up to the projecting platform side. **This guarantees that nothing will wobble and the loads are transferred perfectly into the tree.**

**5. Resilience of the tree – will my tree hold?**

Trees can carry incredible loads!

Wood has an **average compressive strength of approx. 2 kN/cm²** along the fibre, which is the equivalent of **200 kg/cm²**. A round, straight tree trunk, **diameter ø 40 cm**, can therefore theoretically take a load of 1256 cm² x 200 kg = **251.2 tonnes.**

As mentioned above, the tree will most likely not be decisive – **it is the individual fasteners that set the limits – this is 500 – 6000 kg** depending on the fastener and type of wood (more details on the individual fastener types **here**).

**6. Summary – What we have learned**

**Treehouse construction is lightweight construction**– avoid heavy materials such as stone slabs, huge window areas with triple glazing, hardwoods, steel sculptures, dairy cows, …**Never push the load limits of your fixings completely – always work with a safety factor > 2!**This includes**possible defects in the wood and exceptional loads such as violent storms or too many fat party guests.**

Even if the screw can theoretically take 4 tons, it should only be loaded with 2 tons.

- It is better to choose a smaller “backpack”; you can always add on and extend the tree house at a later date if necessary,
**when the tree has become accustomed to the new load!**

If you are unsure about the topics of statics, loads and construction or are planning a public project, then definitely get help from an engineer or carpenter.