Seven stage treehouse design process

There is a lot to learn about treehouses before you start building if you want a safe, long lasting and economical structure. This seven stage workflow will guide you quickly through the basics with links to more detail on this site.

Check the planning/building regulations in your area
Design the treehouse plan before you start cutting any wood
Keep supports separate to the house framework
Allow flexibility in the supports if you use more than one tree
Use single large bolts for attachments to the tree
Avoid restricting tree growth
Build as much as possible on the ground

1. Check the planning/building regulations in your area

In urban areas planning regulations can easily demand that your treehouse is removed on safety, distraction or regulatory infringement grounds.
Every area is different, but some general guidelines apply.
Ask officially before you build.
Speak to your neighbours before you start, because they are most likely to object to a treehouse. Discussing your idea before you start will make it much easier to get their approval.

2. Design the treehouse plan before you start cutting any wood

Involve the client. If the treehouse is for your children, ask them what features they would like and let them help with drawing up the plans. Make sure they feel that it is their own treehouse.
Map the supporting trunks or branches at your proposed floor level. Use string to mark the height on each trunk and draw the layout on squared paper.
Work out the best support method for your particular site. Sometimes designing is easier if you use fewer trees.
Lay out the floor to work out the size limits for the walls and any outside deck.
Draw the house to fit on the floor. The Sketchup web app works well and produces a 3D model that helps to anticipate problems early on.

3. Keep supports separate to the house framework

Aim for a level floor capable of taking the entire weight of the house. The house should be rigid and attached to a solid, flat floor to prevent any twisting of the structure.
Avoid fixing any walls or parts of the roof to branches passing through.
Walls need to be load-bearing and rigid enough to support their own weight plus the roof.

4. Allow flexibility in the supports if you use more than one tree

If more than one tree is used they must be allowed to move in the wind or the treehouse can be easily damaged.
Use either metal brackets or cables to allow flexibility.
Building between two trees is the easiest system for large treehouses. Using more trees means allowing movement in different directions, which is hard to absorb.
A popular flexible design uses a rigid floor unit that can slide over beams below, allowing the beams and the trees to move independently.
To reduce excessive movement, bolt one part of the supports to the largest tree of the set, allowing the other end(s) of the support(s) to move flexibly.

5. Use single large bolts for attachments to the tree

Single puncture wounds at each attachment point cause much less tree damage.
Large bolts are much stronger than screws or nails.
Lag bolts are preferable to through bolts as less damage is caused.
Check fastening ratings and always overbuild each joint to take at least three times the projected weight of materials and occupants.

6. Avoid restricting tree growth

Don't tie straps or ropes around the tree as this will strangle it over time.
Add spacers between beams and the tree to allow room for growth during the lifespan of the treehouse, or use very large bolts which have plenty of the shaft exposed and mount items on the end.
Allow a 2" gap around the tree if it passes through the floor.
Add at least a 3" gap around the tree if it passes through the roof (more if the tree flexes much in the wind).

7. Build as much as possible on the ground

Building on the ground is safer.
Using power tools is easier.
Parts will be prepared faster and more accurately than if constructed in the tree.
Design the treehouse in separately built sections that can easily be joined together—supports, floor, walls and roof. These can then be raised into the tree with a pulley and quickly secured in position.
In remote locations prepare a proper work area before you start. This is a lot safer and prevents small items getting lost.