CMHC Fact Sheet - Basement Leaks

Renovating a Home > Renovation Fact Sheets > Renovating Your Basement — Moisture Problems The following fact sheet is part of the About Your House — General Series Common Situations Moisture is the most common problem in basements — either entering from outside sources or being produced inside by the occupants’ activities. The soil around the walls can contain a large amount of moisture from surface water that is seeping down or from a high water table. Water can find its way inside by gravity or through a crack or flaw in the water protection layer of the foundation. Water can also be pulled up by a “wicking action” or “pushed up” by hydrostatic pressure from the soil under the walls or floor. In the summer, warm moist air from outside can enter the house and lead to condensation on the cool basement walls or floor. Daily activities also produce moisture that can be trapped inside the home. Basement moisture problems often include: Foundation cracks that leak. Standing water. Efflorescence (white, chalky stains). Wet decaying wood in contact with concrete. Damp or moldy walls or floor. Condensation on windows, pipes and other fixtures. Wet insulation. Moisture damaged finishes. Musty or damp carpets. High humidity. Stuffy, damp smells. House as a System A house is much more than just four walls and a roof—it’s an interactive system made up of many components including the basic structure, heating, ventilation and air conditioning (HVAC) equipment, the external environment and the occupants. Each component influences the performance of the entire system. A renovation provides an opportunity to improve how your house performs. Basement moisture problems can have a huge effect on the durability of the entire house structure and on the indoor air quality (IAQ) throughout the house. Avoid Surprises Moisture problems are caused by a buildup of a variety of water sources. Whether it comes from surface or ground water that leaks in, water that wicks up or water vapour that condenses, it must be controlled. The easiest way to control moisture is to stop it from coming in and to exhaust the water vapour produced in the house to the outside. Here are some of the likely situations that people encounter. However, every situation is unique. You may need to hire a qualified professional to do a thorough investigation, find the moisture problems and suggest the best solutions. Foundations Does water leak in through cracks in the foundation wall or floor? Is there a complete concrete floor? Patch small cracks from inside with cement-based material or use an injection-type foundation repair system. Fill large cracks from inside (and outside if possible) with “hydroscopic material that expands as it dries. Consult a structural engineer or basement specialist concerning multiple, severe or expanding cracks. Install a concrete floor over a sealed polyethylene moisture barrier. Water may penetrate cracks, continue to deteriorate the existing house, affect IAQ and any proposed renovations. Severe or active cracks may be an indication of future structural problems or even present unsafe conditions Without exterior protection and drainage, water will eventually find its way inside. Dirt floors are a huge source of moisture and soil gases. Existing problems
	Are there any white, chalky stains (efflorescence) on the walls or floor? Are there any black, white or green mold stains or fuzzy growth on the walls or floor? Are there any wet or decaying wood windows, sill plates, columns or beam ends in contact with concrete? Are floor tiles lifting? Are carpets damp or musty? Is there any wet insulation, framing or moisture damage on finished walls?
	Provide better drainage and dampproofing to the outside. Efflorescence indicates water evaporation of moisture that has wicked through the foundation wall. Clean up mold according to CMHC guidelines. Remove the sources of moisture. Replace decaying wood. Provide a capillary break between wood and concrete. Seek professional advice as damage may compromise structural strength. Damp concrete causes lifting floor tiles and damp carpets. Improve foundation drainage. Install a polyethylene moisture barrier over the concrete floor as part of a retrofit floor system. Replace carpets with hard surface flooring. Remove wet insulation or finishes. Fix the moisture source before refinishing.
	Continued efflorescence is a sign of ongoing moisture problems. Some molds are toxic. Clean up must be done carefully to avoid health hazards. Wood in contact with concrete will continue to decay and will eventually result in structural problems. Tiles won’t stick to damp floors. Damp carpets will continue to be a haven for dust mites and mold. Materials that are wet from any source (leaks, capillary action or condensation) will get moldy and decay, leading to unsightly finishes, durability problems and hazards to health.