Skanska Sweden has produced low energy housing since 2009 using prefabricated concrete sandwich elements, as a cost-effective way to reach high quality and excellent energy performance. Some of these projects have faced problems related to water infiltration due to rainfall during construction, resulting in extra resources for drying the structure, time delays and complicated leakage investigations. If moisture levels remain high when the construction phase is completed, there is risk of moisture damage or inconvenience for the users. Initial interviews and observations at construction- and manufacturing sites reveal some details with large potential for improvement; vertical sandwich element joints, connections between external walls and slabs, external walls and foundation and between balcony door and balcony slab. To improve these details, existing connections and joints were assessed using a list of functional requirements according to Swedish national building regulations that each connection need to fulfil to ensure proper functioning of the building. Suggestions for improvement were gathered and new ideas generated. These propositions were tested by interviewing experts in material purchasing, construction techniques and structural engineering. The study shows that there are many possible ways to improve connection details to avoid water infiltration without increasing energy losses or air leakage.- Vertical joints can be protected from rain using a P-shaped rubber profile or by changing the geometry of the external facade panel. - Leakage from massive concrete slabs into sandwich walls can be prevented by an vertically extended part of the inner concrete panel or a draining channel for installations. - Self-adhesive sealing strips covering the top of the sandwich elements can prevent moistening of the building materials during transport and construction.- Inserting a rubber or bitumen membrane to the inner concrete panel during casting can ensure drainage and prevent leakage to lower structures such as cellars, terraces or parking garages.- Channels in the balcony slab can ensure drainage without reducing accessibility for disabled persons. However, many of the suggested details increase cost and complicate the assembly of the building. Further studies are required to identify the probability and the consequences of water infiltration to assess the accepted cost of preventing actions. Practical experiments are also needed to establish the performance of each new detail. Details should be better presented on drawings to avoid misunderstandings and it is highly necessary that the designer always consider the constructability of a detail. This master thesis does not include finished solutions, but a theoretical evaluation of alternatives of which some have potential to enter Skanska’s system for standardized components after further evaluation.