## 4 Discussion  
In this paper, the drying process of a wood frame walls with high insulation levels has been investigated. The main objective was to examine whether the R-value of the wall influences its drying ability. Experimental tests were set up with a high build-in moisture levels, followed by simulation analysis, which was used to evaluate the drying process in the Finnish climate. The wetting behavior of the wood disks in the drying cakes test showed that wood takes moisture rapidly from the surrounding humid air. This must be considered in the construction site. Wood frames and other wood based structural parts should be weather protected. In details where the drying ability is weaker, the level of built-in moisture must be kept low. The drying cakes test indicated that the lower R-value of the baseline walls did not ensure faster drying rates, compared to the highly insulated walls. In fact, the highly insulated walls had faster drying rates throughout the test even though the Sd-value of the outer part of the BL walls was roughly half of the Sd-value of the HI walls. The largest drying rate difference during phase one was probably connected to temperature differences between the HI and BL walls. The thermal resistance of the wind barrier layer in the BL walls was around 1% and 17-22% in the HI walls from the total thermal resistance of the structures. Therefore, the water vapor pressure difference between the outer surface of wood disks and the outdoor air was higher for HI walls. Later, the drying rates became more alike as the drying was more and more influenced by the moisture transfer inside the wood disks. The results indicated that drying ability in in baseline walls with low thermal resistance is slightly increased with larger U-values. It must be considered that the test assembly did not allow lateral moisture transfer Moisture transfer from a moist wood frame wall is presumably at least two-dimensional in nature. Therefore, the drying results apply to a structural detail without lateral moisture transfer. The wetting phase of the wood frames indicated a strong radial difference in the wood moisture levels. The core of the wood stays drier while the outer surface is highly moistened. The first few millimeters from the surface has the highest moisture content, reaching up to 34 wt-%. These wetting properties probably accelerate the drying process of the wood frame wall, due to the shorter distance of the moisture to reach the wood surface. All the walls showed a high drying rate during the built-in moisture test. At the cold side of the frame, the relative humidity declined slower, possibly due to the lower vapor pressure difference to the outdoor air. The higher RH for the BL wall resulted from the low R-value of the gypsum board. Similarly, the lower RH at the warm side of the BL wall compared to the HI walls resulted from the low R-value of the structure inside the wood frame. The results suggest that using gypsum board behind wind barrier mineral wool has a small effect on the drying rates. However, the minor effect does not rise moisture risks in highly insulated wall structures. At the bottom part of the wall, the low drying rate at the cold side of the BL wall was probably caused by the sealing tape used in the test structure and the high initial moisture content in the cold side of the wood frame in the BL wall. The sealing tape was assembled 20-25 mm over the lower edge of the wind barrier gypsum board. In HI walls this taping did not affect the drying since the 50 mm wind barrier insulation board allowed moisture to dry in the vertical direction. At the warm side of the frame this masked edge type of sealing did not affect drying rates, since moisture transfer spread to a larger surface area. The MC results showed high initial moisture content (over 35 wt-%) for the cold side of the bottom part of the BL wall, which indicated that the initial moisture content in the frame was not even. This reduced the drying rate in the BL wall even more.