First introduced in the industry guide Best Practices for Window and Door Replacement in Wood-Frame Buildings, these rain exposure nomographs are based on those in CSA A440.4-07, Window, door and skylight installation. Bulletin B13-06 from the BC Building and Safety Standards Branch, dated September, 10, 2013, recognizes the nomograph approach as "an acceptable method to determine whether a door is protected. A door deemed to have a Low exposure at the sill using the CSA nomograph method above may use a door with a Limited Water rating."