This specification covers asphalt-saturated organic felt for use as an underlayment in steep slope roofing. The objective of this specification is to provide a finished product that will lie flat and resist wrinkling, puckering, and shrinking when left exposed to the sun, rain, frost, or dew for a period of two weeks after application. In the process of manufacture, a single thickness of organic dry felt shall be uniformly saturated with an asphaltic saturant and the felt shall be produced principally from organic fibers. The surface of the felt shall be uniform and relatively smooth and upon splitting or tearing on the bias, the felt shall appear free of lumps or particles of foreign substances. The material shall conform to the prescribed physical requirements such as tear strength, pliability, loss on heating, liquid water transmission, breaking strength, and dimensional stability, and to the specified dimension and mass requirements such as roll width, roll area, net mass of saturated felt, net mass of desaturated felt, saturation, moisture, and saturating efficiency. The finished product shall not crack nor be so sticky as to cause tearing or other damage upon being unrolled. The following tests shall be taken: (1) determination of saturation percent of felt, (2) determination of resistance to liquid water transmission using water shower exposure test, and (3) test for dimensional stability to low and high humidity. The water shower exposure test for underlayment is illustrated.