Bathroom ventilation: Through the roof or through the soffit?

Editor’s Note: It’s that time of the year again. As the calendar year winds down, we at Canadian Contractor start looking at our “most viewed” stories. Each year for the past SIX, “bathroom ventilation” has made our Top 20 topics! We have no clue why…

Here is a recent post, answering the popular question, “Is it better to vent a bathroom fan through a roof, roof or through a soffit?”

Venting through the roof is often marketed as a better solution, especially by renovators, but in colder areas that receive more snow, soffit is a much better option.

I’ve been in new home building and service for over 10 years and I have seen hundreds of cases of both types of venting. I can tell you that there are far more problems with roof venting. Many contractors just don’t get to see the real failure rates of various systems. From being buried under snow to condensation travelling down the pipe and into the fan housing (that R4 insulation sleeve is doing nothing at 30 below) to ice working its way under the shingles a roof is a terrible place to vent a bathroom in a cold climate. The only option if you insist on roof venting is to put a condensation trap in the pipe and that’s certainly not ideal, either.

When venting out of the soffits – or better yet a gable – the pipe can be fully buried in R40 or R60 insulation, greatly reducing condensation in the pipe. The surrounding soffits are blocked 2 feet on each side. Modern attics are so well vented, anything drafting back up shouldn’t be an issue.

Gable or wall venting is the best, as it keeps the moist air away from the soffit vents altogether. However, with hip roofs being the standard nowadays, it’s rarely an option.

Paul