What is the Difference between Exterior and Interior Foundation Waterproofing?

Exterior waterproofing Toronto

Exterior or Interior waterproofing for your basement.  Which one do you choose?

There are two schools of thought about keeping water out of a basement. One viewpoint believes in stopping it at source. The other lets in it and manages it away. To me it’s a simple matter.  Your first choice is to always fix it from the exterior.  If that’s not possible due various reasons (other homes will be affected, inaccessible area, etc), then an interior waterproofing solution will need to be implemented.

Waterproofing Defined

The dictionary states that “waterproofing” is the act of making something impervious to water. Backpackers waterproof their packs and tents so water can’t get through them. Admitting water into basements and managing it away is the opposite of waterproofing. It’s more of basement water management.

Waterproofing Basements

Waterproofing basements is about denying water access. Anything less is called something else. The process involves:

1  Putting catchment drains on the exterior of the basement at floor level to lead water filtering down away.


2  Treating the outside of the walls with a waterproofing compound or membrane


3  Backfilling the space outside the basement with quality soil, not builder’s rubble


4  Hard-surfacing the result and making sure water can’t pool on it.

This approach applies probability theory to the waterproofing paradigm. For example let’s say the likelihood of water pooling is 5% and that of the waterproofing 1%. The probability of both happening is .05% which is marginal.This belts and braces approach is used all the time.

What Doesn’t Work

The process I just described is specialized. It comes at a cost because digging out and fixing leaking basements properly does take time and is definitely an investment. Some folks prefer to try to skirt the issue by getting an interior waterproofer.  Some companies that claim that all of your basement water problems can be solved from the interior is just flat out wrong.  Applying some sealant on your basement wall won’t do much when water (under pressure) is pushing through cracks and seals in your wall.  You may be able to manage the flow of water once it’s inside the basement, but that’s not waterproofing, it’s water management.  It’s hard to have a dry, finished basement when you have a stream running inside it.

For Small Leaks 

For very minor leaks and cracks, sometimes an interior solution will work, especially if the exterior fix is not an option.  Sometimes they work and sometimes they don’t.  The important thing to know is that the water trying to make it’s way into your basement is under hydrostatic pressure, and is constantly trying to push it’s way through any crack or pore it can get into.

Another Option

If you’ve been through all that and don’t have enough money left over to waterproof your basement properly, then you could try installing weeping tiles and a sump with a pump. In simple terms this involves chopping out a perimeter drain in the basement floor, and using this to lead the water to a deeper point called a sump.

After that you install a submersible pump to remove the water to someplace outside. This is fine if you use your basement as an unfinished space you don’t plan on using for living purposes. But do you really want this in your living space as you’re missing out on a big part of your home that could be a great source of family fun.

Have questions about water problems in your basement?  Contact us here, we’re happy to answer any questions you may have!



The following two tabs change content below.
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.

Leave a reply

Why choose nusite for your next waterproofing project




Customer Testimonials

Interested in working with us? Check out some of our customer testimonials below!

joshua Persaud - yellowpages review

Foundation Repairs

Fixed cracks in my basement wall 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. See More...

Julie Morgan - homestars review

Foundation and Waterproofing Repairs

Fixed several cracks in foundation last spring, had a new central air system installed. the spot where they drilled through the foundation to run the houses to the back of our house started to crack. See More...

DB Markham - Homestars Review


Had Nu-Site in last spring for some warranty work and I'm happy to report they were able to make the repairs to my satisfaction. I especially want to thank the crew that made the repair as they were incredibly efficient! I would use this company again. See More...