To meet the increasingly stringent environmental requirements of Finnish industrialized construction, the E2 Ecology & Economy timber development competition aims to find a conceptual design solution for large-scale production of wooden multi-story buildings. A 15.000 m2 prefabricated wooden development in Kouvola, Finland will serve as a showcase for replicable and locally adaptable cost- and energy efficient housing. Wood as construction material brings a double benefit: remarkably reduced emissions in its production and fabrication and improved energy efficiency of the buildings where it is used. Currently, only a fragment of multi-story buildings utilize timber construction in Finland, a country known for its timber production. BIG’s PUU-BO is a comprehensive prefab solution designed to be both extremely flexible and materially efficient. PUU-BO’s conception as a system based on best practices and not predefined standard elements, gives it an embodied intelligence and ensures its viability for the future. The system’s easy adaptability to a variety of building typologies and uses, opens up new possibilities for prefabricated wood systems beyond the residential market - the very same elements in the residential pilot project could be used in an office building or even a wood skyscraper with no loss in material efficiency.