The CEN/TC250 initiative to form WG2 “Assessment and retrofitting of the existing structures” and after that the Horizontal group under the same title, was motivated by the visible growth and extensive construction activities regarding the assessment and retrofitting of existing buildings and also by engineering works that are aligned with the new agendas for decarbonisation and generally for a sustainable construction sector. The agenda promotes the importance of extending the service life of existing assets, thereby achieving economic, environmental, and socio-political benefits. The scope of the CEN TC 250 SC5/WG12 is to provide general requirements and procedures for the assessment and retrofitting of timber existing structures (buildings, bridges, industrial structures, etc.). The complexity of the current environmental and climate situation reflects on the design practice today demanding an integrated and coordinated planning process. Consideration of all the factors of sustainability leads to complex, integrated design procedures for structures that do not have to satisfy only mechanical properties like before. Therefore the Construction Products Regulation identifies in its Annex I the following basic requirements for the construction: 1. mechanical resistance and stability; 2. safety in case of fire; 3. hygiene, health and environment; 4. safety and accessibility in use; 5. noise protection; 6. energy efficiency and heat retention; 7. sustainable use of natural resources.