Ran across an unusual situation I thought I would kick around here.
Second floor closes washer which has a trapped primary drain to the DWV system with an air gap (okay so far), and a secondary overflow pan below the washer with a trapped pipe to the exterior just above a gutter … hmmmm.
It just rubs me the wrong way … I guess it could be a potential freezing problem, and there would be discharge of waste wash water into a rain drainage system … even though it’s only a secondary drain. Seems like it should have the secondary drain to the DWV also, or at least a float switch in the pan to lock out power to the washer if there is an overflow (instead of the drain to daylight). But I don’t see this situation addressed in any references, model codes (e.g. IRC), or local codes.