The Most Common Type of Basement Leak

leaking basement Toronto where basement floor meets wall
Water leaking through top of foundation wall

As a waterproofing contractor here in Toronto, I’m often asked what is the most common cause of a leaking basement. But first, I want you to conduct a small experiment for me.

Take a used tin can (baked beans, peas, whatever) and remove the bottom end. Then, place the open-ended can in a cooking pot that’s a little taller than it. Hold it down as you slowly fill the pot with water to just below the top end of the can. While you watch:

  • Water seeps into the can past the bottom end
  • The rate increases as the outside water-level rises
  • Finally, the water levels are the same on the inside and the outside

Two things are relevant here. First, there was no seal between the bottom of the tin can and the cooking pot. Secondly, the water found a way inside the can because of what’s called hydrostatic pressure.

Basement Basics

A basement is comprised of two separate structures which are by definition underground. These are:

  • A concrete floor set in an excavated space (the “cooking pot”)
  • A rectangle of four walls standing on it  (the “tin can”)

If you were to fill the excavated space with water, this would place hydrostatic pressure on the structure. In turn, this would seek relief by entering the basement through the concrete floor and walls. These may be well waterproofed; however, as the structure settles, the joint between them weakens and gives way to water pressure.

And that, my friend, is the most common cause of leaking basements. In fact, it’s almost built into the basic design. Just like your camping tent in a storm, the leak is usually at the seam.


Interior weeping tile system image
Interior Weeping Tile System

How to Avoid the Problem

Do you remember how the flow of water into the tin can increase as the water level rose? The same is equally true of a leaky basement. The correct solution is installing an outside drain at floor level. This leads the underground water away as it arrives, so it never builds up enough pressure to become a problem.

In the basement water-proofing industry we call this a weeping tile or french drain system. They’re simple to install during initial construction, but a messy job to repair and install after construction. Getting a certified and insured waterproofing contractor is important if you think you may need this type of work.

Basement First-Aid

In my decades in the basement repair business, I’ve come across countless botched repair jobs involving water-proofing interior basement walls. While waterproofing your foundation can be effective if done properly, if there is an outside water source placing constant pressure on your foundation, it probably won’t last. The hydrostatic pressure invariably dislodges the material, especially since the area was inevitably damp when the seal was applied.

The only solution that’s effective is an interior water-catchment system that feeds a sump pump to an outside drainage point. It’s expensive though. However, it’s also better than abandoning a working basement, which could otherwise add good value to your home.

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NuSite Group is a Toronto based basement waterproofing and foundation repair company that specializes in Basement Waterproofing, Basement Lowering, and Foundation Repairs. Call us today at 416-622-7000 or 905-731-1228 for a free in-home estimate and inspection.

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Customer Testimonials

Interested in working with us? Check out some of our customer testimonials below and find more on Homestars. We are one of the highest rated basement waterproofing companies in Toronto

Mark Lipton - Homestars Review

Basement Waterproofing

Our basement leaked! Of course . . . we bought a 100 year old house! But my office needed to be in the basement permanently. I interviewed 10 different companies until we decided on the Steinbergs and their crew at Nu-Site! They are professional, reliable, courteous, honest, and they really make an effort to communicate with the client about every step of the process.

Sara Jack - Homestars Review

Foundation and Waterproofing Repairs

After several years of chronic leaks, we decided to have our basement waterproofed once and for all. The team over at Nusite was professional, answered my questions during the project and stayed within their quoted price....which is always a concern for me when working with contractors. Great job overall

Joshua Persaud - Yellowpages Review

Basement Waterproofing

Had several cracks in my basement wall and they would leak whenever we had a heavy rain. It started about a year and a half ago and seems to have gotten worse over the past 6 months. I tried having my neighbor seal it, but it started leaking again within a few weeks. Called several waterproofing companies and got several quotes. Finally went with Nusite contractors for the job. They gave a reasonable quote and I liked the guy that came by for the estimate. They stayed within budget and cleaned up before they left. It's been almost 3 months now and it seems to be working great.