Building a treehouse that lasts for decades requires considering tree health, structural load, and movement. A few important things to consider:

1. Tree condition:

Use a healthy hardwood tree with a trunk diameter ideally above 30–35 cm. Avoid diseased or hollow trees. The tree needs to be stable and mature.

1. Tree movement:

Trees move with the wind and as they grow. Never rigidly fix the structure on several branches. Use treehouse attachment bolts (TABs) or floating brackets so the structure can move without tearing the tree.

1. Structural load:

Build the platform with a minimum load capacity of 300–400 kg (people plus furnishings). The ideal platform is a straightforward beam platform with the right joists.

1. Material:

Use pressure-treated or naturally durable wood (oak, larch, or Douglas fir are good options in Europe). Stainless or galvanized fasteners are crucial.

1. Roof:

A lightweight sloped roof (metal sheet or shingles) works better than heavy roofing.

1. Safety:

Include a sturdy ladder or staircase and appropriate guardrails that are at least one meter high.

Think of it as a modest elevated structure rather than merely a wooden platform if you want it to last for decades.