Spring Brought you a Leak in the Basement?

Smell something mouldy, mildew-y or sour coming from your basement or crawl space? Make no mistake: you’ve likely sprung a leak in the basement.

Spring is a likely time of year for moisture problems to arise, and a good time to pay attention to how your basement is weathering the thaw.

As snow melts, air temperatures change, ground and surface water collection increases, and so does the likelihood that moisture could be gathering, causing a leak in the basement. This can lead to a bad smell, and in very little time, turn to mold.

Common wisdom dictates that opening up some windows and drying it out naturally will solve the problem, but in most cases, the opposite is true. While it is counter-intuitive, humidity in the air, particularly in Montreal, can have the adverse effect of further humidifying the basement. A dehumidifier might help a little, but to get to the root of the problem, put on some gumboots and grab a ladder and a spade: it’s time to go digging and fix the grade…


About 90% of damp leaky basement problems are caused by surface water collecting around the building. Only about 10% of problems are due to underground streams and high water tables. Thus, when you call in the professionals and are advised to immediately install French Drains, water barriers, or other expensive solutions, be skeptical: it makes more sense to be systematic about finding the problem. Before you do anything else, do a walking tour around the exterior of your home and check where water could be potentially seeping inwards.

Key things to look at are:

  • Grading
    Check to make sure driveways, patios, sidewalks and the ground slope away from the house. A rate of once inch per foot for the first six feet is recommended, except in the case of asphalt, which only needs to slope slightly to do the job (since it doesn’t absorb water). In the case of lawn and garden areas, adding a little topsoil close to the home will improve the grade; but make sure to compact it well. Gravel is not recommended, since water flows right through it.
  • Above-grade downspouts
    Check your gutters and downspouts to make sure they are not overflowing. If your downspouts drain above grade, make sure the connections are leak-free and continuous. They should discharge into a plumbing system at least six feet away from the building, depending on the slope and porosity of the land.
  • Underground downspouts
    If your downspouts empty into a below-ground plumbing system, check if there’s a concentration of water around the foundation where the downspout enters the ground – this could mean there’s an obstruction or leak in the pipe below ground level. Repairing this means excavation, and could be expensive. While it’s a necessary repair, it’s worthwhile to see if you can switch the downspout to above-grade, which is equally effective.
  • Gutters, Drains, Window Wells, and Cracks
    Clean out your gutters if you didn’t already do it in the fall. (Autumn is the best time to do this.) Make sure basement stairwells, window wells, and other drains are clear of rubbish, leaves and other debris. Make sure window wells are cleaned out. Caulking cracks can effectively block seepage.
  • Check your sump pump: You can test it by lifting the flotation trigger to ensure it does its job. (See the Mose Report post 5-Minute Sump Pump Test)
  • Poke around a little: While a little bit of calcium deposit on concrete walls might not indicate a serious problem, there are other indications that you might need to further insulate your basement from groundwater. Take a screwdriver and poke your posts and joists: if it penetrates, they’re rotting. You need to replace them and you might require the installation of a French drain. In the case of crawl spaces, a heavy-duty liner (similar to a pool liner made of a blend of high-density and low-density polyethylene) might need to be installed.

It’s important to check for moisture frequently. 98% of all basements leak at one time or another, with spring being the most obvious time for problems. But with a little prevention, a little common sense, and a lot of love for your home, your basement could remain free of moisture and all the problems and smells that go along with it.