basement leak in Etobicoke home

Why Your Basement Leaks When It Rains in Toronto

This one’s pretty simple to answer. If your basement starts leaking after it begins to rain, then rainwater is finding its way down through the ground around your foundation.  Your basement is like a swimming pool, except that the foundation walls are trying to keep water out, not in.  As water surrounds the foundation of your home, water finds the path of least resistance and slowly (or quickly if you have cracks in the foundation) finds a way into your basement.

To understand what occurs next, take a piece of raw concrete – this can be any shape – weigh it, put it in a container and top it up with water. Wait twelve hours before removing it and do the following:

  • Weigh it a second time. It will be slightly heavier because it’s absorbed some of the water in the bucket
  • Break the concrete into several pieces and observe how the water has penetrated right through the material
  • Leave the concrete pieces in the sun to dry out. A few days later they should weigh the same as original piece did

Something similar happens when rainwater filters down into the soil surrounding the outside of your basement walls. It gradually saturates them until it reaches the internal surface and oozes through it. This is why it’s so important to channel water away from the foundation walls of your basement. Of course, if you have cracks and other openings, water will start leaking into your basement a whole lot faster.

The Role of Hydrostatic Pressure

This is a term the basement-waterproofing industry likes to bandy around, so let’s take time to understand it. In layman’s terms, it’s the pressure exerted on water at equilibrium – i.e. not flowing – by the force of gravity. The height of the water column acts as a multiplier because of weight. So now you know why dam walls are thicker at the base.


Do you have a wall of water building up against your basement foundation?  If water isn’t being channeled away from your foundation, then eventually water will make its way into your basement.  Eroded concrete, shifting foundations (leading to cracks) and hydrostatic pressure will all eventually cause water leaks in your basement if you leave a swimming pool sized body of water against the outside of your foundation.


The Only Practical Solutions:

Stop the Problem at the Source – If you can prevent all the rainwater from seeping through the earth around your basement then it can’t enter it. Even if you only reduce this by one-half you achieve more because of the multiplier effect I mentioned above.

  • Slope the garden gently away from your house so there are no places where pools of water can form around your foundation
  • Make sure your gutter system is effective and feeds the roof water through downspouts and away down channels
  • Complete the picture by paving (if possible) the immediate area around your house so the problem is completely excluded or use some sort of natural groundcover that is sloped away from your foundation to help whisk water away instead of letting it seep into the ground next to your foundation.


Re-Waterproof the Basement – If you stopped the water leaks completely, that’s great. I’m glad we were able to help you. If not, then here are a few more tips regarding what to do in accordance with the extent of your leaky basement problems.

  • In the case of minor seepage, strip the walls and floor down to raw concrete in the dry season and allow them to dry out completely. Open up and seal all cracks including openings around pipes etc. with underwater epoxy filler. Seal the walls with the best quality waterproofing medium you can lay your hands on. Wait a season to see  how well this works.  You may want to hire a waterproofing company to do it properly as it’s a lot of work to have to repeat.  Just a note, this method is not considered waterproofing as it does not solve the water issue on the outside, just tries to stop water from penetrating your foundation walls.
  • If water still pools on the floor, you can try the less-than-perfect solution of trapping it in perimeter drains and pumping it away. This system (interior weeping tile system) is hardly a pretty sight, but it works. If it keeps the basement dry for an entire year you can conceal it behind some paneling so it can work behind the scenes without you having to see it.
  • If you still have to put your gumboots on when you go down there in the rainy season, then you have groundwater flowing in from surrounding areas. Your only option is to dig down around the outside walls, install exterior drains and membrane the walls. This can be a messy, time-consuming process and due to its nature, should only be done by waterproofing contractors who know what they’re doing.


If the latter solution is your conclusion, find yourself a reputable water-proofing specialist and seek advice. Waterproof your basement the way it should have been in the first place because it can be a big project and you don’t want to have to do it again due to shoddy workmanship.  And if you plan on finishing your basement one day, as many people are in Toronto due to real estate prices, then you really need to do it right the first time or else you’ll be stripping your basement down to the bare walls one day to do it all over again.  Have questions about your leaky basement problems?  You can

Have questions about your leaky basement problems?  You can contact us here, we’re happy to answer any questions you have.  Nusite Waterpoofing is a basement waterproofing company in Toronto, we have been serving the GTA for over 30 years and have an A+ rating with the BBB and are one of the highest rated waterproofing companies on Homestars.



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Waterproofing & Foundation Specialists at Nusite Contractors Ltd
As a family-owned waterproofing and foundation repair business with over 30 years of experience in Toronto, we are proud of our work and stand by it with a full warranty. We’re a service company, working for you. We make sure our customers understand the entire building and repair process, and ensure that our work is done properly and made to last.