According to the Canada Mortgage and Housing Corporation, more than half of Canadian homes have wet basements to some degree. Condensation or leaks in the walls or floor must be corrected, because a damp or wet basement isn’t suitable living space. Moisture problems can ruin even the most expensive renovations and make your basement unlivable. Damp walls and floors result from holes or cracks in the foundation, insufficient dampproofing on the exterior face of wall, poor drainage at walls and footings and site grading that slopes towards the foundation. Wetness may also be caused by a high water table, which exerts hydrostatic pressure on the walls and floor. The following are common sources of moisture that can be the cause of your problem.

High Water Table

The water table varies in depth from area to area and even from season to season. Nothing can be done to minimize water table level, however foundation drains and sump pumps can help redirect water before it becomes a problem.

Eavestroughs and Downspouts

Eavestroughs collect water from the roof and rainwater leaders, or downspouts, and carry it to the ground. When the downspout fails to direct the water away from the foundation, or the grade doesn’t slope away from the walls, this water may leak into your basement. A simple solution is to extend the bottom section of the downspout at least 4-feet away from the foundation, and to adjust the grade around the foundation so that it slopes away from the house.

Cracked Foundation Walls

Although small cracks may be patched on the inside, large cracks and other causes of dampness are best repaired from the outside. This often means excavating around the foundation walls down to the footings. Once the walls and the top of the footings are exposed, it is possible to patch small holes or cracks with hydraulic cement

Window wells

Window wells can collect snow and water, and often contribute to dampness in basements. The base of a window well should consist of 6–8 inches of free-draining material, such as crushed stone, and must be at least 6 inches below the bottom of the window. Installing a length a drainage tile filled with crushed stone from the bottom of the well to the foundation drain, would ensure rapid removal of standing water from the well.

Drainage

Water can seep up through the basement floor, appear at cracks and holes and accumulate at the perimeter where the floor meets the walls. If this occurs frequently or seasonally, it may be the result of an improperly functioning foundation drain. The drainage tile or pipe around the footing may be crushed, plugged or missing, and should be repaired or replaced. The drainage tile should be perforated with holes to collect groundwater, and positioned so that its bottom is below the basement floor. It should also be wrapped in geotextile “filter” to keep fine soil material from clogging the tile. The tile and filter should be covered with at least 4 inches of clear, crushed stone extending to a free-draining zone over the face of the foundation. A length of unobstructed pipe should slope downwards from the foundation drain to the storm sewer to carry away any water that collects around the footings.

Floor drains and sump pumps

If you intend to live in your basement, ensure there is a proper drain with a trap situated at the low point of the floor. The trap should be kept full of water to function properly and should be topped up periodically.

Sump pumps also channel water away from the house. When groundwater fills the tank to a certain level, this activates the pump and typically drains the water into a sewer. While a sump pump can effectively move water from your home, if you have a “high water table”, a perimeter drain system (exterior waterproofing) may also be needed to relieve the hydrostatic pressure.

Backwater valves

A backwater valve is a mechanism that automatically closes to prevent sewage in an overloaded sewer line from backing up into your basement. A properly installed backwater valve should be located to prevent sewage from coming through any fixtures in your basement, such as sinks, toilets, showers and laundry tubs. Installing a backwater valve can protect your basement renovation from serious damage, such as that which often occurs during periods of heavy rain.

Floors

Dampness and cold can also enter a basement floor from the ground beneath it. Building codes require an occupied basement in a new house to have a moisture barrier, such as polyethylene, beneath the slab.

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