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Steve Payne   

Should a bathroom fan in Ontario be vented through the roof or through the fascia?

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Carmen asked us the building codes in Ontario generally say about the proper location on a house (the roof or fascia/soffits) for venting bathroom fan air to the outside. Bathroom fan expert Glenn Curtis, Soler Palau Canada, has the answer.

Question from a reader, Carmen, about bathroom exhaust fan venting:

“I would like to know, when venting a bathroom exhaust fan should it be vented up through the roof? Getting different opinions. Some say yes, some say it should be vented through the fascia. I live in Ontario, so does snow on roof change things?”

Response from a bathroom fan expert, Glenn Curtis of Soler Palau Canada, a manufacturer of bathroom fans – among other products.

It is really a matter of choice as to where the bathroom fan is vented to the outside, as long as it exhausts directly outside. The good majority of bathroom fans are vented through the roof, while some people are choosing to soffit vent them as an alternate. There is no definitive answer in the codes that pertain to where the air must vent out of the house. One thing to keep in mind, though, if choosing to soffit vent the fans, especially in Ontario, is that you are exhausting warm, moist air from the bathroom. In the middle of winter, this can create a situation where the exhaust point may become frozen and create a blockage.”



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24 Comments » for Should a bathroom fan in Ontario be vented through the roof or through the fascia?
  1. Carmen, Not a lot of houses are or were built with raised heals on the trusses or stick framed that way so when venting through the soffit you end squishing a 3-4″ pipe with an insulation blanket on it through a very small slot between the plywood and the top plate of the wall. This is a restriction already but more importantly the loss of insulation at that same point on the wall. Unless you have 16″ raised heals on the trusses where the insulation is maintained at the now R50 and then go over that and into the soffit area I would not do it. The other matter is let the heat rise instead of forcing it down.

  2. Steve Mills says:

    Due to convection, air is drawn into the vented soffits and expelled through roof vents. Do you want warm, moist air that accumulates around the soffit vent to be drawn into the attic? Didn’t think so.

  3. Stan says:

    if the vent does ice up, at least sunshine will thaws and clear the roof vent. Vented heat and freeze/thaw from a soffit vent can also contribute to roof ice dams at the eaves.

  4. Mike C&E Contracting says:

    I was told a long time ago, that the soffit is what catches all of the breeze/ wind from the outside to get flow through the attic.This air would then vent out through the roof vents (this is how we get attic ventilation).
    That being the case; that means; you have warm/ moist air trying to vent out as outside air/ wind is blowing in. This would cause a condensation issue inside the pipe. It could also cause that moisture to travel back into the fan housing. If you were to vent through the soffit, use a fixed open vent (usually used for HRV), with the open venting facing the house.

  5. cornwall renovation says:

    The bathroom exhaust should NEVER be vented anywhere near, nor through the soffit area. Cooler air which is found under your roof overhang (soffit) is drawn up through the perforations of the soffit and exhausted through your roof venting system. By exhausting warm moist air in that area you will most certainly cause a mold problem in your attic (usually very evident on the underside of the roof sheathing close to the area where where the exhaust outlet is found,) Play it safe and vent through the roof.

  6. Michael Glovre says:

    I don’t think it should be fitted in the soffit area because that would be the worst thing to do unless you want hot air running through your heads in the bathroom, especially in a house like mine with two elders. I have got people from Toronto( ) come and fix the bath safety products. They examined the ceiling and pointed this mistake.

  7. Ron says:

    Here in the North, we vent the bathroom exhaust through a bulkhead to the exterior wall, the exhaust ducting is insulated and has a slight slope to the exterior wall to allow any condensation to escape, we also install a 5′-6′ length of plywood at the eaves so the exhaust can’t get into the attic space.

  8. Sandra says:

    the I have had frost on the inside roofing above the bathroom. I believe it is in line with the bath tub. I’ve had two thoughts. I hope that there is insulation between the tub and outside wall. The other is that there could and may still be a problem with how the exhaust fan was connected. A friend said that the corrugated tubing that was used was not attached correctly and they attached with some screws but I wonder if that would be sealed enough. Do you know if there would be an easy way for me to check if there is proper insulation behind the tub. The tub is a full tub and shower fiberglass unit. I thank you for any feedback.

  9. Len Peeters says:

    Most of the issues I’ve had with condensation damage have been with bathroom exhaust pipes in the attic. Also roofs tend to leak where things go through them so the more holes you cut the more risk you take. That being said the soffit option with vented soffit allows heat and moisture to flow into the attic in an unnatural fashion which could lead to roof rot if the attic venting is insufficient.

  10. Jason says:

    Make sure your pipe is insulated from the warm fan into your cold attic. Condensation can run back into the fan.

  11. Diana Murphy says:

    Is it against code for a bathroom fan to be vented to another room instead of outside?

    currently experiencing this on a rental – fan is in a public washroom and the bathroom smells get fanned into the public reception area.

  12. Questo says:

    In my opinion all Ontario homes bathrooms exhausting fans should be connected into a main pipe an end that at queens park, with a high speed blower, may be the only way the Liberal squanders be force out.
    Hey Ontarians we are in big economic trouble, taxed up to our necks.

    This new cap and trade bs is no ganna last longer, its a fraud like many others to grab money from all of us. In Australia the government had to abolish this bs cap and trade, before total economic collapse.
    Some of our politicians are really stupid, to the point of inanity.

    Happy new enslavement year, welcome to the mob rule. More debt, more lies, more bla bla bla + hst+cap/trade+all others trades fees+ more insanity …… Are you happy GTA for voting in this insane squanders?

  13. Robert says:

    My bathroom fan discharges directly into the attic for 27 yrs and there is
    no sign of mold or rot so I installed the new one the same way; I have a 5ft peace of dryer hose with a hump in it so as not to let cold air flow back into the bathroom and insulation on top of it and I’m in northern Ontario
    I don’t know what all these EXPERTS are talking about

    • Tom Holden says:

      My bathroom and range hood both have exhausted into the attic for several years. I’ve checked periodically and see no problems. Recently, I connected them to gable vents and am now plagued with slaps from the exhaust flaps caused by gusts and wind noises such as low moans.

  14. Mike McNeil says:

    we are having problems with moisture from a bathroom vent out the side of the house near our back door. the door freezes up in the winter. what would you suggest we do to relocate the vent?

  15. Mike McNeil says:

    the vent now is not direct. would a roof vent not cause freezing problems as in soffit, or blockage.

  16. Doug says:

    Hey Steve,
    When venting a bathroom fan through the roof, is there any building code regarding the size of the vent pipe(3″ 4″)? Or the type of pipe to be used (ABS)? Or the height the pipe must extend from the roof? Does the code specify top hat on pipe vs candy cane shaped to prevent rain accumulation?

  17. Dennis White says:

    Basement in a town Row row house ( i only have 2 outside walls. I have been told I cannot vent thru the attic : to far of a run for a bathroom exhaust fan .
    I have a basement hydro dryer venting out the lower front wall of my unit : my bathroom is just steps away . Since both exhausts will be carrying warm moist air ….to the outside , Why can i not use the (offset Y ) in new exhaust to the dryer vent that is already thru the wall . There has been No moisture build up from the dryer ( Ice in the winter ) and My understanding when the bathroom fan is not in use the damper is closed ?
    I am not venting toxic fumes and the toilet is in a water closet ( so not even odors) …Just venting the occasional shower steam ( Moisture)

  18. Paul says:

    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 dor over 10 years and seen hundreds of cases of both types of venting, and can tell you there are far more problems with roof venting. Many contractors just dont’ get to see the real failure rates of various systems. From being buried under snow to condensation travelling down the pipe and into rhe fan housing(that R4 insulation sleeve is doing nothing at 30 below) to ice working its way under the shingles its a terrible way to vent in a cold climate. Only option is to put a condensation trap in the pipe and that’s certainly not ideal either

    When venting out the soffits or better yet a gable, the pipe can be fully buried in r40- r 60 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 shouldnt be an issue.

    Gable or wall venting is the best, as it keeps the moist air away from the soffit vents all together, however with hip roofs being the standard nowadays, its rarely an option.

  19. Stephane Boisjoli says:

    I disagree with this opinion. A roof vented fan takes it’s toll on the shingles. If you vent it through the roof, get the vent that blows away from the shingles as much as possible.
    I can see an upside down V shaped line from the roof vent on the shingles, those shingles are more worn.

  20. Hari says:

    Hi Steve,

    I had a two-bathroom renovation about one year ago. Recently I started having water drippage through the bathroom fan. When I investigated it, I discovered that the bathroom one fan duct was just left hanging in the attic without connecting it to vent and the second bathroom fan did not even have a duct — there was just direct venting in the attic. When I contacted the owner of the Reno company he said “there is no need to connect the duct to vent in the roof.” Is that true? I am very concerned about mold and mildew. He does not seem to want to address it.

  21. Noel Murphy says:

    I disagree with venting moist bathroom air into the soffit, I have seen the results, when the damp air is up-drafted into the attic. I have been a renovating contractor for 27 years, specializing in upscale bathrooms, (design & build). I have been a CPI (Certified Property Inspector) for 22 years, now retired. Ventilation is critical in every building, especially in residential dwellings, where the health and well being of the residents should be of primary concern, Noel Murphy, (CPI Retired).

  22. Hithere12 says:

    1/ Exhaust to the roof. A contractor needs to install a PVC ( not alluminum) gooseneck on the roof to cover rain and snow. It must have a bird prevention net, no flapper (backdraft damper on the gooseneck or you get frozen ice and it shuts in the Winter. Your fan already has a backdraft damper installed.
    2/ Vent it to the side of the house is the best method like the dryer vent.
    3/ Don’t let any cowboy vents bathroom air to the soffit. Air just takes all that moisture up to the attic and you get mold in there.
    Hire a HVAC contractor from Home depot or a from reputable company. Stay away from Jack of all trades from craigslist.

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