Bathroom exhaust vented to soffit?
We live in North-central Alberta where it can be very dry but has been humid this year. Winter temps can reach -40 C. We will be replacing our 3-pc bathroom exhaust fan (and ducting) with something more powerful and Energy Star rated. Currently it is vented through the soffit which I’ve been told is allowed here. But my insulation contractor wants to vent it to the roof since I am replacing everything. I am a little worried about leaks and condensation and snow in winter if I do that but also about the moist air re-entering the attic through the vented soffit if I leave it. A gable end vent would be a long run and go through either stucco or aluminum siding. Am I okay to vent to the soffit? Do I have any other alternatives? Will insulation keep it from condensing if I go through the roof?
We have been opening the bathroom window lately (aluminum slider) instead since it’s summer but it is directly below the vented soffit where the exhaust vent is – is that better? Worse?
Also – are there any IC rated heat lamps? Or a way to seal it properly? We’d like replace or remove the current one since it can’t be insulated over.
Thanks
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
I share your concerns as my bathroom exhaust fan does this too, and I had always considered that I would go through the roof when I remedied the issue...until I read Martin's response to the question "What's the best way to vent a bathroom fan", found here.
https://www.greenbuildingadvisor.com/community/forum/general-questions/25233/whats-best-way-vent-bathroom-fan
I am in CZ 7 (Very Cold, Moist) FWIW.
Thanks Pete. I wonder if another solution could be to have a non vented piece of aluminum soffit put where the vent discharges?
I found an old Alberta Energy $avers "Ventilating Your Home" pamphlet from the 90s at the Hardware store - shows exhaust fans on interior walls running down and under the floor before exiting the house. Can't see that being feasible for a retrofit!
Kim,
My own preference is for gable venting. If there is no gable, you go through the roof. Soffit venting is not recommended -- it should only be used if all other alternatives are impossible.
What if the gable end has vented soffit on the eaves? My roof is not a steep slope so the gable ends aren't very large. They also have ugly triangular aluminum gable vents at the peak. Would the roof be preferable then since the air would have 2 routes to go back to the attic?
Kim,
It's your choice -- you are the one who is on site who can assess the advantages and disadvantages of each location.
Thanks Martin. I guess I will just have to pick one and hope nothing bad happens.
I have a related question, not sure if I should be starting a new post.
Anyhow, I noticed in the exterior of the second floor of my grandma's house (a Vancouver special built in 1986 in BC) that there is no visible exhaust vents for two bathrooms either through the roof, the side of the house or in the soffit. The bathroom on the main floor I can visibly see and feel the bath exhaust on the side of the house The second floor baths both have ceiling mounted bath fans, are above small windows and are about 1 foot away from the exterior wall. Removing the fans I see there are ducts, but cannot see where the duct leads to. I've been in the attic and cannot see the bath fans as the roof slopes downwards and the area where the fans are mounted cannot be accessed from up top. I have not gotten a chance to bring a tall ladder to look under the soffit yet but I suspect that the fans are vented to the soffit area but unfortunately they have no specific outlets.
My question is, if I see that the bathroom is vented to the soffit, is a possible solution to just install a soffit vent? Ideally I would run a new vent going out the roof, but this is not possible because her roof is made with clay tiles. A big concern with just venting to the soffit is that the warm, moist air will get drawn into the attic leading to a mold problem as the existing soffit is vented aluminum. In this situation is it best to close off the vented soffit to prevent the air from re-entering the house? If so, how many feet to either side?
Any suggestion is greatly appreciated.