Abstract This rapport contains a comparison between in-situ cast joists and prefab joists. We have looked closely at the aspects that should be taken into account when selecting the method and what should be most efficient economically and timely. The work we have done has been with the guidance of Peab Sverige AB in Linköping. It begins with a basic background and theory in the field. Then we conducted interviews with various players that we believe may have an impact in the method to be used, including project managers, site managers, carpenters, concrete workers and installers. In addition, we made visits to workplaces where they use different methods and at Skandinaviska Byggelement in Katrineholm, where prefab slabs is manufactured. We also visited PERI AB's head office in Halmstad. PERI AB is a form provider in Sweden. In our study comparing the same item in different methods such as reinforcement, connections, installations, time to dry out, transport, etc. It is apparent that certain elements are almost identical for the two approaches while the other elements vary considerably. The factors that determine which method should be used are many and differ to some extent also between different regions and enterprises. In Östergötland and Örebro one were more positive about the site cast joists. We believe that there is no reason to depart from a concept that works and giving profits to the company. In southern Sweden, there is another point of view which is almost completely different from the cast on site between the beams and aiming instead for prefab slabs in apartment buildings.