Bathroom exhaust fan critical to maintaining dry home
QMy daughter and her partner bought a River Heights bungalow last November. It has a bathroom that has a window in the shower wall and no fan in the bathroom. The plan is to eventually use this as a guest bathroom and build a nice new bathroom downstairs. However, until money is saved and that happens, I am wondering if it is a good idea to purchase a dehumidifier and use it in the bathroom after showering to get rid of excess moisture. They don’t have any mould or mildew on the ceiling but I am afraid that eventually there will be some. Also, they have cedar wall panelling in this bathroom and were told not to paint it as it absorbs the moisture. I don’t know if a bathroom fan can be added. It would probably be expensive and would have to go through the attic and there could be asbestos insulation in there. What are your thoughts? Dawn Chappellaz Answer: Bathroom ventilation is critical to maintaining a dry interior home environment and preventing moisture damage and mould growth. While the current older window may be adequate, if used diligently, upgrading to an exhaust fan will absolutely be necessary in the future. As many people know, moisture is the No. 1 enemy of all things home related. In our interior house environment, the largest sources of moisture are normally from the kitchen and bathrooms. Getting that moisture to the exterior of the home, before it can cause serious problems, is critical to maintaining healthy indoor air quality. When your daughter’s home was built, the older window would likely have been adequate for bathroom ventilation, due to a large amount of air leakage common with that age of home. The air leakage through the old windows, doors, attic, and basement would have been enough to naturally allow enough fresh air intrusion to prevent most serious moisture issues. Untreated cedar is a good choice for this age of bathroom, as it is open-poured and does readily absorb and release moisture, but should not be installed inside the shower enclosure. If the bathroom window is opened every time an occupant takes a shower or bath, year-round, that would normally be enough to allow excess water vapour in the air to exit the building without significant condensation on the walls or ceilings in the home. If the kitchen window is also left open on moderate to warm days, or when cooking, little evidence of moisture damage may be present in the home. Even to this day, this may still work relatively well if no major upgrades to air sealing have been done in the home. If the house still has a furnace and water heater which vent through the original chimney, and windows have not been upgraded to well-sealed modern PVC units, there may still be a lot of air leakage through the building envelope. If attic or basement insulation has not been substantially upgraded, that will further allow fresh air from outside to leak into the interior environment. While this significant air intrusion may not be good for the heating bills, it may ensure that the air inside the home during the heating season is sufficiently dry. The problems may begin to occur when your daughter and partner begin to do major upgrades to the older home. Replacement of an older furnace with a new high-efficiency unit is often the first item to cause higher indoor relative humidity (RH). This is caused by sealing the existing chimney. The old chimney may be a major source of exfiltration of moist air from the home, as the exhaust products from the furnace are diluted by house air that goes up the chimney during the heating cycle. Once this is closed off, all of that moist air stays inside the home. This upgrade is often combined with a further tightening up of the building envelope by replacement of older windows and improved basement, wall and attic insulation. All of these improvements will not only be good for the environment and the wallet, but they make the home more comfortable in the frigid winters. The downside is that these modifications will prevent much of the previous air leakage, keeping the moist house air inside much longer. This will undoubtedly raise the RH in the home, providing an ideal environment for mould growth and moisture issues. To counteract the rise in RH inside the home as improvements are made, your daughter and partner will have to make accommodations to get the humid air outside, while bringing in more fresh air for replacement. The simplest way to achieve this goal is by use of mechanical systems to move air through the building envelope. This is where the bathroom exhaust fans comes in. Simply opening the bathroom window may no longer be adequate to ventilate the bathroom, due to the larger amount of dissolved water vapour in the house air. The window may also freeze up quicker in the winter, preventing good operation, for the same reason. That is why installation of bathroom fans are so critical when upgrades are made. The fans will work best in conjunction with some form of fresh air intake, which may be as simple as an insulated duct connected to the return air plenum of the furnace, or as complex as a heat recovery ventilator. The level of upgrades to the building envelope may dictate which method is most practical. Installation of a bathroom exhaust fan will be critical as future energy efficiency improvements are made to the home, but may not be that difficult or costly. Installation in the bathroom ceiling, venting through the attic, may be the most straightforward approach. If there are issues with asbestos containing insulation, or difficult access to the attic, fans which vent though exterior walls or the foundation will be an acceptable alternative. Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out
his website at trainedeye.ca.