| 摘要 |
PROBLEM TO BE SOLVED: To prevent the leakage of rain water entered from gaps between roofing materials having air permeability and moisture permeability by using fabrics or nonwoven fabrics made of water swelling fibers. SOLUTION: A roof underlayment is desired to have a water absorption magnification A, an amount of water absorption B and a bulk density C which are in the following ranges: A>=30 (times), B>=3000 (g/m2), 0.30 (g/cm3) >=C>=0.025 (g/cm3). If the bulk density of water swelling fibers is small, permeation occurs in a short duration before swelling occurs even when a gap between fibers is large and water absorption magnification and amount of water absorption are sufficient. On the contrary, when the density is increased with a fixed weight mass, the thickness of nonwoven fabrics decreases accordingly, and water passes through and permeation occurs within a time when fibers contact water and swell. Even when a weight mass is large or density is too small, time is long and water leaks through this duration. Thus, rain water entered during typhoon or the like is absorbed and water leakage is prevented and also moisture generated indoors can be easily absorbed and dew condensation indoors can be prevented.
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