In the current situation a big part of the settlements that exist in Sweden is in need of renovation and energy efficiency in order to survive. Therefore, also many of the older houses with a wooden structure are in a need of energy efficiency, which can be done in a variety of ways, including adding insulation. This project deals with whether the use of a diffusion barrier or a vapor barrier affects a wall structure by adding insulation to an older house with a timber frame. The insulation materials which are concidered in this investigation are mineral wool and wood fiber insulation. Efforts are focused on the effects of moisture on these insulation materials. To demonstrate the differences that arise the moisture measurement program WUFI have been used to simulate a variety of wall designs. These designs are developed in consultation with the construction carers who are active in the industry. Using WUFI graphs illustrating the moisture levels of the wall structures were obtained and from these conclusions vould be drawn. The work demonstrates the differences that arise when using a diffusion barrier or vapor barrier in wall construction. The differences between an external and an internal insulation is also depicted in this work. In addition, mineral wool and wood fiber insulation are compared. Conclusions drawn from the work is that if you have an interior insulation the most advantageous is to use a diffusion barrier in the wall construction. If you have an exterior insulation, however, the most advantageous is to use a vapor barrier with varying water vapor resistance.