The challenges for soffit installations can be met by using a vent that bends out from the building, forcing the exhaust away. They can also incorporate grilles to block entrance to critters and dampers to prevent the return of cold outside air.
Bath vent fan duct routed down through a cathedral ceiling to the outdoors: This article illustrates installing a bathroom exhaust fan in a cathedral ceiling over a steamy shower. The exhaust ducting is sloped downwards and terminates in a soffit.
But while you can't have two fans with one vent, you can make one fan and one vent serve two bathrooms. This setup requires an in-line centrifugal fan mounted in the attic drawing air simultaneously from both bathrooms (see photo). A grille in each bathroom attaches to ducts, which then fasten to a "Y" connector at the fan.
In the past I was a big fan of soffit vents. I figured if you used quality vents with a good back-draft damper, and sealed and insulated the duct well, it was a great way to vent bathrooms. There are several key benefits: First and foremost, it av
2009 IRC, new construction, single-family. Contractor wants to run the exhaust from bath fans through the soffit to the outside. Is a bath fan an appliance; and if so, can he use Sec. 1804.2.6?If he puts a solid soffit at least 4' in either direction from the center of the exh. outlet (screened louver, etc.), would this then be a compliant install?
Other venting options includes running the duct up through the roof or down through the soffit. Note that the bathroom vent fan must always exhaust to the outdoors; never allow the duct to simply blow into an attic, crawlspace or other enclosed area.