The industrialized timber housing process is capable nowadays to build multi-storeyhouses since fairly new changes in the Swedish regulations where made after theadmission of the European Union in 1994.The industrialized process moves parts of the construction process into a highlyeffective factory where 3D-volumes of the building are prefabricated beforetransportation to the building site for assemble.The assembly process is relatively effective compared to the completion of thebuilding service system and this is therefore the main focus in this thesis. This thesisattends problems with completion of the building service system, and thereforedemarcates from other aspects, such as technical and economic aspects, of thebuilding service system.The degree of completion of the flats differs from completion of the connectivepassages, for example hallways, in a way that suggests a need for further investigation.This thesis includes analysis of the possibilities to increase the prefabricatedconnective passages, to the extent of containing building service systems.An increase of the prefabrication of the building service system has a greatdevelopment potential, even though some restraining factors need to be solvedbefore implementation.This thesis was made in collaboration with two of Sweden’s leading companies on themarket of multi-storey industrialized timber housing, Moelven ByggModul AB andLindbäcks Bygg AB.