## 2 Materials and Methods
### Test Set-Up for Built-In and Leakage Moisture in Wall Structures
It was important to achieve an equivalent moisture load in all four test walls to be able to equally evaluate the drying out capability of the structures. Therefore, the water insertion system, shown in Figure 1, was designed in a way which made it possible to add the same amount of water in each test wall during every irrigation event. The water insertion was positioned in each wall structure, correspondingly, to represent rainwater leakage into the thermal insulation layer behind the exterior material layer(s). The pointwise insertion position is depicted in Figure 1, in the side view and in the horizontal cut. The insertion method has the benefit that the added moisture will retain in the structure and not run off, as would occur if the water was added, e.g., in either of the surfaces of the ventilation cavity. The water was injected into the structures with a PVC-hose and hand pump, which were calibrated for the presented accuracy. The air pressure in the hose removed the remaining water droplets from the inner surface of the hose. The insertion method is similar to the one used in [15]. The amount of leakage moisture was evaluated based on the rain statistics in Helsinki during years 2010-2018 [16] and rain measurements in Finland during 2000-2002 [17]. The month with most rainfall in Helsinki (93 mm) is August, whereas the average rainfall per month is 58 mm [16]. The total rainfall per year is, on average, 712 mm [16]. The dimensioning rainfall per month was selected to be  
Figure 1: The test setup in the built-in moisture and leakage moisture tests. 150 mm, which has only been exceeded in two months during the second decade of the 21 st century. During the summer months, the average rain time is 6.17% (44.4 h) [17] and the average long-term rain duration is four hours [16]. The horizontal rainfall is thereby 3.4 mm/m\({}^{2}\)h. The vertical rainfall on the building facade was calculated from the horizontal rainfall with the equation presented by [PERSON] and [PERSON] [18] to be 1.15 mm/h. Here the rain admittance factor (RAF) was set to 0.5, the driving rain factor (DRF) set to 0.225, wind speed set to 3 m/s, and the direction of wind set to 0 deg. These values correspond to average conditions during rain in the middle of the facade. The ratio of water leakage to water spray rate in a previous laboratory experiment was between 0.1 and 6% [15]. The amount of water directly injected into the thermal insulation space was selected to be 1% (0.0115 kg/m\({}^{2}\)h) of the vertical rainfall impinging the building facade. Considering the test wall size of 0.6 m\({}^{2}\), the injected water amount was 0.0069 \(\pm\) 0.0001 kg per wall every 38 h, on average (phase one). The rain leakage test was started with a small amount of water to avoid water outflow from the test structures, which has been the case in a previous study [19]. In the case of water outflow, the drying-out ability of each structure could not be evaluated precisely. This risk of leakage water outflow from the structures was somewhat increased by the relatively small size of the test specimen (wall section, 0.6 \(\times\) 1.0 m\({}^{2}\)). One might argue that, in wood frame structures, the height of the test structure is not imperative to the drying-out ability since most of the water would accumulate in the lower part of the test structure. Thereby, the drying-out ability would be determined by the properties and dimensions in the lower part of the structure. The injected water amount was subsequently triplicated to 0.0207 \(\pm\) 0.0001 kg per wall every 67 h, on average (phase two) based on the measurement results, and this amount was considered significantly larger than in stage one, yet moderate. The total leakage amount was 0.1035 kg in phase one and 0.3135 kg in phase two.