## 4 Discussion
Furthermore, the drying rates between HI walls showed that the PA-vapor barrier did not enhance the drying rate, which is consistent with an earlier study [27]. This was due to the high drying rate towards outdoor and elevated indoor moisture levels. The highest RH behind the wind barrier coating in wall HI2 was probably caused by the lower Sd-value of the vapor barrier, resulting in a higher moisture diffusion rate from the inside air. The results from the rainwater infiltration test showed that the small leakage moisture inserted into the insulation cavity of a wood frame wall did not have an adverse effect to the hygrothermal behavior of the structures. Relative humidity varied between 55-85% in the outer part of the structures. This indicates that the fault tolerance of vapor open (Sd 0.07-0.17 m) baseline and highly insulated structures against leakage moisture was at a high level. With a larger leakage moisture, an increasing trend in the RH and MC values was evident for most of the measurement points in the walls. Further, the level of the RH and MC changes indicated that most of the leakage moisture still dried out of the test structures. However, the experiment results imply that recurring larger leakage events lead into ascending moisture contents in the structure and eventually into moisture damages. The thermal insulation level of the structures did not significantly affect these tendencies in the behavior of the structures. At the bottom part of the wall, the risk for moisture damages can be slightly higher for baseline walls compared to highly insulated walls. The results imply that PA-vapor barrier and gypsum board behind wb-mineral wool or as the weather barrier layer can, in the short term, equalize relative humidity changes in the insulation cavity, connected to rainwater infiltration. The validation of the simulation model demonstrated that it is possible to evaluate the drying process of a moist wood frame with acceptable accuracy by adoption of correct water vapor diffusion coefficients. The diffusion coefficient of wood must include the strong dependency on the relative humidity. The simulation results indicated that the drying ability of the wood frame wall is not remarkably different between baseline and highly insulated walls. If the drying will take place during summer, a BL wall with 100-175 mm mineral wool insulation can dry slightly faster compared to a HI wall with 300 mm insulation, during the first 1-2 months. If the drying starts in autumn, the drying rates are almost identical between walls with different insulation levels. This behavior can be associated with the low water vapor pressure in the outdoor air. With a high drying potential, the drying rate of the wood frame is determined with the moisture transfer inside the wood frame. The highest drying rates can be obtained with highly insulated structures, using moderate insulation levels (300-350 mm), and by using 50-100 mm mineral wool outside the wood frame. The risk for mould growth during the drying phase was low for all walls. The maximum value of the mould index, approximately 0.6, was found on the rigid boards of walls BL1 and BL4, which is below the limit of 1.0, standing for growth detectable by microscope. The most common highly insulated wall type, HI1, had very low mould index (0.065) and, in this sense, performed better than the BL1 wall. The results implied further, that a plywood weather barrier might cause moisture problems in structures with high built-in moisture levels, regardless of the U-values of the structures. A gypsum board as weather barrier can lead to slight mould growth, especially if the drying phase starts in autumn. If using a thermal insulation as wind barrier, the risk is diminished. The third investigated rigid board, a fiber cement board, did not imply mould risks due to its the resistance against mould growth.