Wikipedia
Brettstapel is a massive timber construction system, fabricated exclusively from softwood timber posts connected with hardwood timber dowels. It is a relatively simple method of construction that exploits low grade timber, not normally suitable for use in construction, to form load bearing solid timber wall, floor and roof panels.
Brettstapel works by using hardwood dowels with a moisture content lower than that of softwood posts. Over time the dowels expand to achieve moisture equilibrium thus 'locking' the posts together and creating a structural load-bearing system.
It is one of a few construction methods that can be entirely fabricated from timber. Although some variations do still use glue and nails, these are not necessary and avoiding these means a healthier indoor air quality can be achieved. The timber itself locks in vast amounts of carbon dioxide without emitting harmful toxins found in other materials, benefiting both the user and the environment.