The aim of the study is to increase the understanding and knowledge of the climateimpact of a timber construction built as a vertical extension of an existing building compared with corresponding timber building built on the ground. The purpose is to make a life cycle analyse of the construction phase and to investigate possibilities to improve the climate impact of future vertical extensions with interventions in the planning phase when decisions on material selection and constructive design are usually taken. 

The system boundaries have been the same when comparing the vertical extension withthe building on the ground, as a prerequisite for a robust comparison.

The results of the environmental calculation for the timber vertical extension show that what mainly contributed to the climate impact in the studied case was the steelreinforcement that distributes the load on the existing building. 

The results of the environmental calculation of the building on the ground show that the basic structure, ie an insulated slab on ground with stiffening under dividing walls in this case entails most of the total climate impact during the construction phase. 

An important conclusion of the study is that the choice of reinforcement measure is of great importance in an extension. Careful review of the existing building's condition and load-bearing capacity is required. Material, material quantity and structural design need to be evaluated so that the climate impact can be minimized while maintaining function.