Ask any constructional worker and there is a high probability that this person knows a colleague with pain or other disorders caused by working with power tools. According to the Swedish Work Environment Authority 71 percent of the Swedish constructional workers is exposed to vibrations at least 25 percent of the working hours. Despite this, the number of reported occupational sicknesses caused by vibrations is as low as 1, 4 percent. JM Ltd. is one of the largest constructional companies in Sweden. Their main business is new housing and development of residential areas. God quality and low impact on the environment is a part of great importance in the company’s long-term goals. To achieve this, and to ensure an effective production, the activities have gradually been organized according to Lean production. In the year of 2010 the producing part of the company began to use methods originating from Lean such as process orientation and standardization of work procedures. JM calls this Structured production. The purpose of this thesis is to investigate how working according to Lean when producing apartment buildings interacts with a safe working environment. The goal is to investigate and identify problematic operations during the assembly of semi-prefabricated, non-bearing walls so-called perimeter walls. The method used is a time study conducted in spring of 2014 on construction sites in Stockholm. The exposure to vibrations from power tools on construction workers, when working according to the installation instructions applicable at JM’s building projects was examined. The study revealed that the action value determined by the Swedish Work Environment Authority was exceeded when installing perimeter walls according to the installation instructions. The conclusion is to extend measurements and medical surveillance of exposed operations and personnel. A package of equipment and materials to be used when installing perimeter walls is presented along with possible methodological improvements of the installation instructions.