Bathroom Windows 

Question: I am renovating a home with significant damage to the bathroom caused by condensation on the bathroom window. Should I remove the window and refinish it to match the existing walls? 

Older homes – pre-1980s – often had windows installed above the tub for natural lighting and ventilation. The problem with this approach is that in the winter, warm, moist air condenses and then freezes on the window pane and sill. This becomes a problem when the resulting water infiltrates the wall cavities beneath the window or in behind the wall finish. Older windows were often wood, which further promoted mould growth. Vinyl tub surrounds were often chosen as the wall finish because of the lower cost when compared with ceramic tiles, but these are subject to expansion and contraction, allowing moisture to infiltrate at seams and edges.  

Today’s best practice is to install one-piece tubs and showers and bathroom exhaust fans in new-house construction. While it may be a good idea to install a one-piece tub and shower when refurbishing a bathroom, refinishing the exterior to match may be problematic, especially on stucco finishes or discontinued claddings.  

An alternate solution is to install a fixed vinyl window with frosted glazing. Ensure that the sill and jambs are sloped to drain any moisture condensation, and that the edges are sealed with a bath and shower silicone caulking compound. If you are not replacing the window, install a vinyl covering or ceramic tiles to the sill and sides, again sealing the edges to prevent moisture from entering the wall cavities. 

Glass blocks may be another alternative. These are becoming increasingly popular and can often be found at recycling depots at a modest cost. The advantages of glass blocks include increased thermal efficiency ratings and looks. Ensure that the sill is sloped to drain water away from the opening, and use ceramics tiles to finish off the opening.  

Whichever option you choose, ensure that when remodeling a bathroom, you install a bathroom exhaust fan to expel the moisture-laden air to the exterior. Bathroom exhaust fans can be connected to the light switch, in conjunction with a timer or a humidistat, which measures the relative humidity and turns itself on and off according to predetermined levels.  

See the CMHC pamphlet from the About Your House Series entitled “The Importance of Bathroom and Kitchen Fans,” CE 17, and “Before You Start Renovating Your Bathroom,” CE 28e. 


Part of the Eagle's Eye on Housing series - read more