In Belgium, the concrete industry is very powerful, with the consequence that 95% of the buildings are built with concrete. We are convinced that, in a changing world where CO2 is a planetary issue, human kind has to build its cities with a maximum of timber. We have to use timber. We have to plant trees. We have to renew our past forests. However, timber is not competitive : a precast prestressed slab (called”hourdis” in Belgium) can reach spans of about 14 meters with a thickness of 45 cm and a price of a tens of euros per square meter. At the same time, timber has already a cost of around 100 euros per cubic meter even before any transformation (cutting, gluing, etc). The only solution to make timber competitive is thus to use it as raw as possible, but also to assemble and prepare it with robotic arms. In collaboration with Belgian companies Imax-pro and Mobic, we have ongoing researches related to two fields : on the one hand, slabs composed of half raw truncs covered by concrete, and, on the other hand, reciprocal structures also composed of raw truncs.