I have a challenge on my second floor where a curved steel roof insulated with spray foam makes the best option for a half (toilet/sink) bathroom fan's vent to route down and laterally out the side of the home. I know appliance vent pipes need to keep a slope up and out. But a "fart fan" - is there any code prohibiting the vent duct to go down and over?


I don't think there is any restriction against an exhaust going downward.

A slightly downward direction is standard in some installations, like when a soffit exhaust vent (common in extremely cold and snowy environments) is used with a fan box which sits above the ceiling joists.

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    I spoke with inspector - For a forced air (fan) exhaust it is ok to go down and across. Outlet can be on side of house if more than 10' from window or any air intake and not in a walkway. – phoenixAZ Jan 9 '15 at 17:28

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