雨掛かりを考慮した外壁通気構法の水分挙動に関する研究（その1）：通気層への雨水浸入および外装材吸水が壁内湿度に及ぼす影響

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  • STUDY ON HYGROTHERMAL BEHAVIOR OF WALL ASSEMBLY WITH VENTED CAVITY IN CONSIDERATION OF DRIVING RAIN (PART1): IMPACT OF RAIN PENETRATION AND WATER ABSORPTION OF EXTERIOR SYSTEM ON HYGROTHERMAL BEHAVIOR WITHIN WALL ASSEMBLY
  • アメ カカリ オ コウリョ シタ ガイヘキ ツウキコウホウ ノ スイブン キョドウ ニ カンスル ケンキュウ(ソノ 1)ツウキソウ エ ノ ウスイ シンニュウ オヨビ ガイソウザイ キュウスイ ガ カベ ナイ シツド ニ オヨボス エイキョウ

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<p> The wall assembly with vented cavity using the siding is installed for durable improvement in many wooden houses. The houses with less projected eaves built on very narrow and small properties are increasing in recent years. According to an investigation of moisture damage by authors, many of houses which internal condensation occurs were built in less than ten years. Deteriorated siding and joints in these houses have potential for water absorption and rain penetration. It is considered that these accumulated moisture have significant impact to cause the internal condensation within stud cavity, when surface temperature on the siding raises by solar radiation. However there are few studies regarding hygrothermal behavior in consideration of these impacts such as water absorption and rain penetration at outside finishings.</p><p> To unravel mechanism of the internal condensation due to moisture cause the rain water, lab-experiments and field measurements were conducted. In the lab-experiments, water penetration rate and water absorption coefficient of sidings were quantitated. In the field measurement, the internal condensation was reproduced by intermittent injection of rain water into the vented cavity. Additionally, the drying performance of different ventilation configurations were compared by humidity and moisture content variations within wall assemblies in field measurements. The findings of the study are as follows;</p><p> (1) Quantity of rain penetration form siding joints : Quantity of rain penetration from siding joints of four installation methods were measured by water spray test. It was confirmed that there were significant differences in the amount of water penetration between the installation methods. In the cases which condensation occurred, the water penetration rate was 5 to 12 % at low wind speed. From the result, it is considered that intermittent rain penetration occurs with high frequency in rainy day.</p><p> (2) Water absorption test from siding surfaces : Quantity of water absorption of siding with chalking and sound one just after the testing are 0.62 kg/m2 and 0.06 kg/m2 respectively. This result is suggested that the quantity of absorption water increased with deterioration of the surface coating due to aging. In addition, since water was absorbed just after water absorption, it is considered that water is absorbed and retained every time it rains.</p><p> (3) Impact of rain penetration and water absorption of exterior system on hygrothermal behavior within wall assembly at the experimental house : For the external finishing of the experimental house, deteriorated sidings were installed to four types of vented cavity. To verify hygrothermal behavior within wall assembly, authors reproduced intermittent long-term rain penetration into the vented cavity, and measured the temperature, humidity and moisture content variations.</p><p> Authors confirmed that moisture accumulation in wall assembly being reproduced on east side of the wall, when the moisture retained in the sidings and vented cavity was released into the wall assembly. This phenomenon was caused when the surface temperature on sidings were raised by solar radiation after rain. Especially in case of the configuration with low ventilation performance, the condensation occurred for 10 to 13 hours in daytime. As for the configuration with secured ventilation performance, the internal condensation did not occur.</p><p> In conclusion, aforementioned results verified that the moisture condensation at the vapor retarder due to rain water was caused by co-occurrence of several factors, i.e. rain penetration, water absorption, insufficient ventilation and solar radiation.</p>

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