Staining and/or moisture dripping through or around the bathroom fan is a common issue during the winter. The best thing that you can do is run the fan consistently (for at least 20-30 minutes during really cold days), and make sure that your bathroom is cleared of humidity before you turn off the fan.
It is also good to double check your current humidity levels in the house, as humidity levels can also affect this.
Here is a rule of thumb for humidity levels:
* 40% humidity when temperature is above 0º Celsius
* 35% humidity when temperature is above -5º Celsius
* 30% humidity when temperature is above -10º Celsius
* 25% humidity when temperature is above -20º Celsius
* 20% humidity when temperature is above -25º Celsius
* 15% humidity when temperature is above -30º Celsius
You also want to ensure that your thermostat isn’t set above 22º Celsius. If you still notice moisture or frost building up around windows, then your humidity level likely still needs to be adjusted lower (or it could be a sign that there are potential issues with the seal around the windows).
Following these initial guidelines – the next thing we would look at is the ducting, as well as the fan unit. When inspecting, we look at the ducting to make sure it is insulated, making sure it has a “catch” at the base of the duct. This is where the ducting runs horizontally along the attic floor before running up to the roofline for approximately 3ft.
This “catch” at the base of the duct works to catch moisture that drips down the duct before it has a chance to drip back down through the fan. We ensure that the catch doesn’t have a negative slope (as that can cause the duct to fill up with moisture and cause further issues), but can handle small amounts of water. As long as the fan is run regularly, then the moisture should evaporate out of this catch before it has a chance to build up to the point of dripping back down through the fan. We then ensure that the ducting is properly sealed to the existing fan, as well as to the gooseneck on the roof. This ensures that your fan isn’t dispelling moisture into the attic space through gaps or seams at the ends of the ducting.
If all of the above look good and you are still having issues, then sometimes the issue is simply the fan isn’t strong enough to push the moisture through the duct to the outside, or the damper on the fan is potentially stuck open. In which case, we typically look at replacing the fan with a stronger one (higher CFM rating).
If your leak is coming from some other “random” patch(es) on the ceiling, or on the ceiling along the outside of the house, then the issue could be attic rain or ice damming. Attic rain happens when there is heat loss from the living space that moves into the cold attic, which causes the air to condense and create frost. When the weather warms up, or the sun hits the roof in those areas, the frost can melt and create attic rain.
ATTIC RAIN can be mitigated by having proper insulation levels, ensuring that the vapour barrier in the attic is properly sealed, and that there is proper intake and exhaust venting in the attic space to help circulate the air.
ICE DAMMING can also be a result of heat loss from the living space and improper ventilation. If the attic space is too warm, then it warms up the underside of the roof deck and can start to melt the snow on the roof prematurely.
The snow then melts and drains to the eave, where, once it hits the cold metal will start to freeze. This can cause a build up and allow water to dam up behind the ice, which can then back up through the shingles and cause a leak. This staining is typically noticed on the ceiling along outside walls.