4 ways to find and prevent leaks in a finished basement

By Jon Labelle

With a growing number of Toronto area homeowners making better use of their basements than storing boxes, it's likely you've also finished the area to extend your living space. Before closing things in, you probably took the time to do proper basement waterproofing of the concrete walls and used only below-grade products to reduce excess moisture and mold.

But what if the basement was finished before you moved in? What if, even after you did everything possible to protect the space against flooding, you still have water in your basement? You may have noticed a trickle of water along the kitchen cabinets, a wet area in the carpeting, noticeable water stain on the drywall or a lingering odor every time you enter the room.

There's no need to panic. Just because you have some water in your basement, doesn't mean the room has to be disassembled to find the leak. There are a number of places you can look for problems well before any dismantling is required:

1) Take a walk outside

Instead of tearing down wallboard or paneling inside your basement, take a look outside. You'll want to find the top of your foundation wall. It should be exposed a few inches above the grading. If not, pull back the soil with a shovel to uncover the wall. Now, take a wire brush to clean off the wall surface and slowly examine the wall for hairline cracks. A flashlight might be helpful in locating smaller cracks (some may only be 1/16" wide).

Pay close attention to those areas that correspond to the interior seepage. Identify the general area where you found water inside, measure the distance from a window or corner, and find the same spot on the exterior wall. In some cases, there will be a crack in that general area.

While it is common to have between two and eight cracks in your foundation, many of them will be shallow and won't leak. Generally, the cracks that extend all the way through the wall are the type that will allow water infiltration. Be sure you've actually found cracks and not form lines made when the wood forms were removed after pouring. These are purely superficial and won't cause any seepage issues.

If you find a crack, it's time to do a little more research. Although you may be anxious about your finding, reading articles like, "Foundation cracks and when to start worrying" should give you better insight as to your next course of action - repair with sodium bentonite clay, add a waterproofing membrane, install or repair exterior drain tile or look for another cause. All these repairs can be completed from the outside without disturbing your finished space.

2) Check the windows

Leaky windows may seem to be a minor problem, but an ongoing issue can lead to mold growth and water damage to your finished basement. Many older homes in Toronto and the GTA area weren't designed to provide living space in the lower level. It's possible your finished room was created through a basement underpinning project where the floor was lowered and windows were added.

Water leaks through basement windows can be corrected with caulking. You can apply the caulk to the exterior, but be sure the frame isn't rotted. If so, you'll need to repair or replace the window to correct the problem.

If your windows are below grade level, you should consider installing window wells. This curved steel insert is installed outside the window with a drain and gravel to safely redirect rainwater and snowmelt away from the foundation. Plastic covers can reduce the amount of water and debris that enters the well for additional waterproofing protection.

Make sure the grade around your window is sloped away from the house, gutters are free from debris and downspouts are extending a safe distance from the foundation. Pooling water against your window from any of these sources can contribute to leaking and interior damage.

3) Play detective inside

Old sump pump

If you've taken precautions outside and you're still experiencing seepage in your finished area, you'll need to start hunting inside for the source. The sump pump and water heater are likely hidden in a utility room away from your living space. Your water heater may have sprung a leak or the sump pump may not be operating properly.

Other classic problem areas can be traced back to plumbing leaks on the first floor. Check under sinks for leaking pipes. Dishwasher hoses can become worn or loose and leak down through the floor or behind walls. Slow leaking toilets can go unnoticed for an extended period of time, so make sure they're in complete working order.

4) Stay proactive

It's common for basements to experience dampness regardless of whether the space has been finished or not. Running a dehumidifier during summer or high-humidity months will keep condensation levels down.

While it may be easy to ignore moisture issues in your finished basement, taking a proactive approach to waterproofing will protect your investment and keep the room looking new. You can handle the majority of these remediation projects with a few tools and little construction experience. More complex repairs can always be safely handled by local waterproofing professionals. By staying ahead of leaks, you'll be able to enjoy your lower-level living space for years to come.

Jon Labelle is an expert in the field of home improvement and remodeling with extensive knowledge and years of experience. Every homeowner’s best friend!