1.1 This test method covers a procedure for determining the water permeability of coarse granular materials used in the drainage layers of vegetative (green) roof systems. 1.2 This test method addresses water permeability under the low-head conditions that typify horizontal flow in vegetative (green) roof applications. 1.3 This test method is suitable for coarse-grained materials with 100 % of the material retained on the U.S. #8 [2.25 mm] sieve. It is not suitable for finer-grained materials. 1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and to determine the applicability of regulatory limitations prior to use. 1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.