Interior waterproofing installs a drainage channel and sump pump inside the basement to collect water after it gets in. Exterior waterproofing digs down to the footing, seals the wall from outside, and stops water before it reaches the concrete. Interior work costs less and finishes faster. Exterior work addresses the source but needs excavation space that many older Toronto lots do not have.
What each method actually stops
Interior and exterior systems solve different problems, and mixing them up leads to paying for the wrong fix.
Interior waterproofing cuts a channel along the inside edge of the basement floor, lays drainage pipe next to the footing, and connects it to a sump pump that ejects water outside. It manages water that has already crossed the foundation wall. It does not stop damp walls, efflorescence, or slow seepage through porous concrete, because the wall itself is never sealed.
Exterior waterproofing excavates along the outside of the foundation down to the footing, applies a waterproof membrane or coating to the wall, and often adds or repairs a footing drain (weeping tile) that carries groundwater away from the house. It stops water at the source and relieves hydrostatic pressure against the wall, which is the pressure that causes cracks over time.
Crack injection (epoxy or polyurethane) seals a single active crack from either side and is a narrower repair, not a whole-wall system. Some of the foundation repair companies in Toronto in our data offer this alongside full waterproofing.
Cost comparison
Figures below are typical ranges reported by Ontario contractors and price guides in 2026. They are not quotes. Get at least two written estimates for your specific wall length and access conditions before you decide.
| Factor | Interior waterproofing | Exterior waterproofing |
|---|---|---|
| Typical cost per linear foot | $70 to $150 | $150 to $350 |
| Typical whole-basement cost | $3,000 to $15,000 | $10,000 to $35,000 |
| Excavation required | No | Yes, full depth to footing |
| Landscaping and driveway disruption | Minimal | Significant, often multi-day restoration |
| Stops water at the wall | No | Yes |
| Works on a shared property line wall | Usually yes | Often not possible |
| Typical timeline | 2 to 4 days | 5 to 10 days, longer with limited access |
Source: DryShield Cost Calculator, Southern Ontario.
Lot access in older Toronto, North York and Scarborough houses
Exterior waterproofing needs equipment access along the wall being excavated, usually a mini excavator or, where space is too tight, a hand-dig crew. This is where many older neighbourhoods run into limits:
- Shared driveways. Semi-detached and rowhouses common in older parts of Toronto and Scarborough often share a driveway with the neighbouring property. Excavating the wall on that side needs the neighbour’s cooperation, and some driveways are too narrow for an excavator at all, which pushes the job to hand digging and adds cost and time.
- Side-yard setbacks. Houses built close to the property line, common in North York’s older postwar streets, may only have two or three feet of side yard. A contractor needs to confirm that is enough room to dig a safe trench without undermining the neighbour’s foundation.
- Mature trees and retaining walls. Roots and hardscaping near the foundation can turn a straightforward exterior job into a more careful, slower one, or rule it out on that wall.
- Party walls. A wall shared directly with an attached neighbour cannot be excavated from outside at all. Interior waterproofing, or crack injection from inside, is the only option on that wall.
Before you assume exterior waterproofing is possible, walk the perimeter with a contractor and confirm equipment access on every wall you want treated. A quote that skips this step is incomplete.
What our board data shows for these three towns
Our directories rank companies by Google rating and review count, not by us testing their work. The counts below are from the basement waterproofing companies in Toronto, basement waterproofing companies in North York and the related trade boards in the same three towns, current as of September 2026.
- Toronto basement waterproofing: 20 companies ranked, median rating 5.0, median review count 100. Every company on the board has 20 or more reviews.
- Toronto foundation repair: 20 companies ranked, median rating 5.0, median review count 76. Three companies on this board have fewer than 20 reviews, so check individual review counts before assuming depth of track record.
- North York foundation repair: 20 companies ranked, median rating 4.95, median review count 53.5. Four companies have fewer than 20 reviews.
- Scarborough foundation repair: 19 companies ranked, median rating 5.0, median review count 26. Five companies have fewer than 20 reviews, the widest spread of the three towns for this trade.
A high review count is not a guarantee of fit for your job. It tells you how many customers left feedback, not whether that company handles shared-driveway excavation or party-wall interior work. Use the review count and rating as a starting filter, then ask each contractor directly about access on your specific lot. You can browse full rankings, including company profile pages, on the waterproofing contractors board for Toronto and the mold removal companies board for North York, relevant if long-standing dampness has already caused mold.
City of Toronto subsidy: what it covers and what it does not
The City of Toronto runs a Basement Flooding Protection Subsidy Program for homeowners. As read on the city’s own page today, for work completed on or after November 12, 2025, the subsidy covers:
- Up to $1,600 per backwater valve, to a maximum of two devices, at 80% of invoiced cost.
- Up to $2,250 for a sump pump, plus up to $300 for a battery backup, at 80% of invoiced cost.
This subsidy applies to plumbing devices, not to waterproofing membranes, drainage tile, or crack injection. If your basement problem is groundwater against the foundation wall rather than sewer backup, this subsidy will not offset the waterproofing cost itself, though a sump pump is often installed as part of an interior waterproofing system and may qualify on its own. Confirm current eligibility and amounts on the city’s page before you budget, since these figures can change.
North York and Scarborough properties fall under the same City of Toronto program, since both are part of the City of Toronto for municipal services.
How to decide
Start with what the water is actually doing, not with a method you have already heard of.
- If water enters through the floor-wall joint or a floor drain during heavy rain, an interior system with a sump pump is often the more direct fix, and it avoids excavation limits entirely.
- If the wall itself is damp, cracking, or bowing, that points to hydrostatic pressure from outside, which only exterior waterproofing relieves. Pair this with a foundation repair quote if you see horizontal cracks or wall movement.
- If one or more walls cannot be excavated (party wall, narrow shared driveway, no side-yard access), plan for interior treatment on those walls regardless of what you choose for the rest of the house.
- If mold or a musty smell has already developed, get a moisture source diagnosis before paying for remediation. Waterproofing without fixing the entry point means the mold returns. See the mold removal companies in Toronto board if this applies to you.
- Get quotes for both methods where your lot allows it. A contractor who can access your exterior walls should be able to quote interior and exterior scopes side by side so you can compare against your actual wall length and access conditions, not the general ranges above.
Frequently asked questions
Is interior or exterior waterproofing better for an old Toronto semi?
Interior systems usually fit better on old semis and rowhouses because they do not need wide side-yard access. Exterior work needs room for an excavator or hand digging along the full wall, which many shared driveways in Toronto, North York and Scarborough cannot provide.
Does interior waterproofing stop water from entering the foundation wall?
No. Interior waterproofing collects water after it has already passed through the wall or floor joint and routes it to a sump pump. The wall itself stays wet. Exterior waterproofing seals and drains water before it reaches the wall.
Can I combine interior and exterior waterproofing?
Yes. Some homes get an exterior membrane and footing drain on the accessible walls, then an interior system on the walls that cannot be excavated, such as a party wall shared with a neighbour. Ask a contractor to quote both scopes separately so you can see what each side covers.
Does the City of Toronto subsidy cover waterproofing membranes?
No. The City of Toronto Basement Flooding Protection Subsidy Program covers backwater valves, sump pumps and a home plumbing assessment, not membranes, drainage tile or crack injection. Check the current amounts on the city’s own program page before you budget.
How long does each method take?
Interior systems typically finish in two to four days because the crew works inside on the slab. Exterior excavation on one wall commonly takes five to ten days including backfill, landscaping repair and driveway or walkway restoration, longer if a shared driveway limits equipment access.