Article summary
TLDR: Interior and exterior waterproofing systems work identically—both use Delta MS membrane, weeping tile, and sump pumps. The key difference: exterior protects the foundation wall itself (costing $10,000-$30,000+), while interior manages water after it passes through ($4,500-$13,000). For Toronto renovations and home additions, interior waterproofing typically provides sufficient protection at lower cost, especially when property access is limited by garages, utilities, or tight side yards. Before either system, fixing grading and downspout drainage solves 90% of water issues. Choose waterproofing when making substantial basement investments to protect against future damage.
Are you trying to decide between interior or exterior Waterproofing? Look no further.
When planning a home addition or basement renovation, you'll face a waterproofing decision that could swing your budget by $17,000 or more.
We see this play out constantly. A homeowner gets told exterior waterproofing is superior. And it is, technically. But superior doesn't always mean necessary.
We're currently planning a home addition in Rosedale where the client was quoted just under $30,000 for exterior waterproofing. The interior option? $13,000.
Why the Massive Cost Difference
Access drives everything.
That Rosedale project had a natural gas line, an attached garage, and limited side yard access. Exterior waterproofing would require hand digging around obstacles, rerouting utilities, and potentially damaging existing structures.
Most Toronto homes have similar constraints. Air conditioners sit against foundation walls. Porches extend over footings. Driveways run tight to the house.
Each obstacle adds cost. Interior waterproofing typically runs $4,500 to $10,000, while exterior systems cost $10,000 to $15,000 or more when access gets complicated.
The System Misconception
Here's what most homeowners don't realize: interior and exterior waterproofing operate identically.
Both systems use Delta MS membrane against the foundation wall, connecting to weeping tile that captures water. That weeping tile feeds into a sump pump basin, which discharges water away from your home.
The only difference? Exterior waterproofing protects the foundation wall itself from water exposure. Interior waterproofing manages the water after it passes through.
For renovation projects, that distinction matters less than you'd think.
When Interior Makes Sense
We evaluate three factors: access, foundation condition, and project scope.
For that Rosedale project, we worked with our engineer to inspect the foundation walls from inside. The 80-year-old foundation was in excellent shape. No major cracks, joints between the CMU blocks were intact, no visible water damage.
That's the assessment that matters. We look for cracks, water stains, or deteriorating mortar joints between foundation blocks. Most older Toronto homes have CMU or brick foundations, so joint integrity tells us everything.
If we find significant damage, we present both options with real numbers. Sometimes the cost difference narrows, and exterior becomes worth it. But often, interior waterproofing provides sufficient protection at a fraction of the cost.
The 90% Solution Nobody Mentions
Before discussing either waterproofing system, we check something simpler: drainage.
Proper grading away from your foundation, with downspouts terminating at least 10 feet from the house, solves almost 90% of water issues.
That's not an exaggeration. Most basement moisture problems stem from surface water pooling against foundations.
Fix the grading, extend the downspouts, and you've eliminated the need for a $13,000 to $30,000 waterproofing system in most cases.
When You Actually Need Waterproofing
The trigger point is simple: substantial basement investment.
If you're building a legal basement apartment, finishing a recreation space, or adding living area through an addition, waterproofing becomes your failsafe system.
You're not just protecting against current water issues. You're insuring against having to rip everything apart later. Given that 60% of homes experience basement moisture at some point, that insurance makes sense when you're investing significantly in below-grade space.
The Decision Framework
We present both options with transparent costs. The client makes the final decision with complete information.
That Rosedale homeowner redirected their $17,000 savings into other project areas. They got sufficient waterproofing protection without the excavation complexity.
For renovation projects, interior waterproofing usually provides the best value per dollar. It's not inferior. It's appropriate.
The key is understanding what you're actually protecting, what your foundation condition allows, and what your property access realistically permits.
About BVM COntracting
BVM Contracting is a full-service General Contractor or Home Builder located in Toronto. We provide home renovation and building services for major home renovations and custom home builds (full interior renovations, home additions, lot severances, new home construction, garden suites, and laneway suites). Our goal is to help guide our clients through the process of building their home, from concept to completion.
Further than providing General Contracting and Project Management for major home renovations, we also offer value-added services such as renovation financing, renovation rebate consultations and services, building permit and design services, smart home installation services, and real estate investor services.
To learn more about our offering by visiting our services page. Learn more about our vision, mission, and values here.