Renovation & Design

Proper ventilation required to keep attic high and dry

Questions: We moved into a bungalow with a low-sloping roof four years ago. Last winter, and this winter, we started having problems with the amount of snow on our two bathroom rooftop vents, and one oven rooftop vent. Last year, the snow was so high above the gooseneck style vents that water entered the attic from the oven vent and water came back down through the fan in the bathroom. There was a lot of ice buildup from the hot humid air escaping through the vents. I went on the roof and removed the snow and that fixed the problem for the moment. However, going on the roof after each snowstorm is not safe or sustainable. Each vent is also in an area where there is a lot of snow buildup.

As I see it, my options are to stop using the fans in winter, which is not a great thing, but better than having water in the attic. Shovel the snow off the vents several times a year, which is not safe. Or, redirect the vents from the roof to the side and then either remove the roof vents and cap the holes in the roof, or leave the vents to act as simple attic vents.

Option three is possibly the best long-term solution, but also the most complicated and expensive. Since our roof is so low sloping, there is no room to run an exhaust pipe from the bathroom vents to the side of the house, as both bathroom vents are near the center of the roof. There is not enough space in the attic to vent new air ducts. The exhaust vent for the oven is easier to fix since our oven is against the exterior wall and we could make a hole in the side wall there to have a side vent. However, this causes another issue, can the hot exhaust run back into the soffit and the attic. Also, could cold air and outdoor noise be a factor with having an exterior vent so close to the oven?

One contractor suggested running exhaust pipes from the bathrooms down to the basement and out the side. However, how efficient would this be trying to push hot humid air down to the basement and out? Could the two bathroom exhaust pipes be redirected into our current HRV unit? The advantage is that we would not have to make another hole in the side of the house for exhaust and use less piping to get it outside. We currently have one basement bathroom vent that runs to the HRV unit. However, using the HRV certainly does not have the same suction power as a dedicated exhaust pipe for a bathroom fan only. Which option do you suggest?

Thank you for any suggestions you may have, Paul Doyle.

I do not use my bathroom fan in the winter, so I blocked off the openings thinking it would prevent warm air from getting into the attic. I once had an insulation contractor come in and they said too much condensation is entering the attic, hence the occasional leaking in my living room. Is this a good thing for me to do?

Thanking you in advance, Lynda.


Ensuring good ventilation from bathrooms and kitchens is essential to preventing condensation and moisture issues from occurring in attics. Rerouting problematic roof vents and ducts may be the only way to prevent periodic leakage, unless you are very diligent about regular inspection and snow removal.

I am answering both of your similar questions, which came in response to my last column about snow-covered plumbing stacks. While the second respondent has taken the unusual step of not using and covering their bathroom exhaust fan, the first home’s moisture issue may be easier, but more costly, to address.

In response to Lynda’s direct question, the direct answer is a certain no! It is a very bad idea to stop using the bathroom exhaust fan in the heating season and blocking it will do nothing to help the situation. Both of those actions will only help drive more humid air into the attic. Firstly, the humid air from showering and bathing must be exhausted out of the bathroom as quickly and efficiently at possible to prevent mould growth in the bathroom. Secondly, covering the fan and discontinued use will only help drive more moisture into the attic due to the stack effect, which has been discussed numerous times in this column. So, a better solution would be to insulate and air seal the bathroom fan duct and housing in the attic, or replace the entire system if it is not properly functioning, but never discontinue its use.

As for the first home in question, having a low-slope roof can make entering and alterations within the attic very difficult. As discussed above, your first option of discontinued use is a no-no. Relocating the vent hoods to the gable ends, with improved insulated ducts above the ceiling, is a viable option but will depend on how accessible the attic is. The third option is certainly the best option, depending on the configuration of your HRV. It will likely require opening up some walls to run ducting directly to the basement unit, but will allow complete removal of the ceiling fans, ducts, and roof vent hoods, which will certainly stop the leakage. Having the HRV cross-connected to the furnace blower should allow it to move the air through the home properly, as long as it is properly installed and set-up.

Removing rooftop snow that is covering your exhaust fan vent hoods may be the simplest solution to periodic leakage, but certainly not the safest or easiest method. Relocating the vent hoods and ducts, or installing new ducting connected to a good HRV, may be better choices but will add significant expenses to the fix.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and a Registered Home Inspector (RHI)( Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at


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