We are renovating a second floor bath in a circa 1976 dutch colonial with 15:12 roof from the eaves up, breaking to a 3:12 pitch to the peak. The front facing dormer where the bath resides is under a 2 1/2:12 pitch shed roof starting at the main ridge to the dormer eaves. If you’re still following all this, here’s the problem.
I need to install an exhaust fan and duct it out of the bath. Straight up will send it through the 2 1/2:12 pitch roof – not good for sealing the boot. I’d rather not send it out to soffit and have an ugly hood thing on the front of the house. Routing ductwork to the main attic and then to a gable vent would be very difficult due to lack of access. Question: does exhaust ductwork have to have a continuous upward pitch like a plumbing vent? Could I send it down about 6′ on an inside wall, elbow out to the crawl space under the 15:12 pitch and then out through that roof? Anyone else had to get creative with exhaust duct routing?
Replies
yes you can. It's done all the time around here. Many times we run them down into the unfinished basement area and then outside.
I wouldn't change direction more than once though, and I wouldn't go down and then up. You don't want a place for moisture to collect, which is the issue with bathroom exhaust fans, unlike plumbing stacks that need to vent gases.
Good point about down and up, best route would be just down and out, if it's possible. Also, use PVC instead of metal ducting, (providing it meets code in your area) PVC will be much less apt to promote condensation than metal.