Overpour Underpinning
The Fast & Affordable Way to Lower Basements
Overpour underpinning is one of the fastest and most cost-effective engineered methods for basement lowering, especially in older homes where the foundation needs a wider and stronger base before deeper excavation, waterproofing, drainage upgrades, and installation of a new concrete slab. This method has a quicker construction cycle and is typically the lowest-priced underpinning option, making it a practical choice for many Toronto homeowners.
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What Is Overpour Underpinning?
Overpour underpinning is a foundation construction and reinforcement method where a portion of the existing footing is removed and replaced with new concrete that overlaps the original footing and ties directly into the foundation wall. As part of this process, the interior offset of the old footing is carefully removed, creating a straight and clean surface that allows the new footing to extend outward and form a wider, stronger structural base. This added width increases support for the structure above and prepares the basement for safe lowering.
Overpour foundation underpinning remains one of the most commonly used and dependable methods for basement lowering in Toronto because it adapts well to older homes and delivers predictable, long-term structural stability.
Underpinning Menu
Overpour Underpinning Process
1. Section Layout & Preparation
The foundation wall is divided into engineered underpinning sections. Equipment, lighting, shoring posts (if required), and dust-control barriers are set up to prepare the basement for safe excavation.
2. First Stage Excavation
The first set of underpinning sections is excavated to the engineered depth. Soil is removed under the original footing to create space for new concrete footing.
3. Original Footing Adjustments
In the overpour underpinning process, the interior offset of the existing foundation footing is carefully removed. This creates a straight, clean surface that allows the new concrete footing to overlap the original footing and tie directly into the foundation wall. By eliminating the inward step of the old footing, we can form a wider and stronger structural base, which is essential for safe basement lowering and long-term foundation support.
4. First Stage Building & Structural Inspection
A structural engineer inspects soil conditions, footing preparation, and excavation depth to confirm compliance with the engineering plan and the Ontario Building Code.
5. First Stage Forming & Concrete Pour
Forms are installed and concrete is poured into the first-stage sections. A concrete vibrator is used to ensure proper consolidation and remove trapped air. The concrete foundation cures for 24–48 hours.
6. Second Stage Excavation & Pour
The second set of underpinning sections is excavated and formed. A building inspection is completed and must be passed before concrete placement. Concrete is poured, vibrated, cured.
7. Third Stage Excavation & Full Dig-Out
The final underpinning sections are excavated along with full basement excavation to the new lowered height. A third building inspection is performed at this stage.
8. Third Stage Forming & Concrete Pour
The last underpinning sections are poured, vibrated and cured. Once all stages are complete, the basement is ready for interior waterproofing, drainage work, and installation of the new concrete slab.
Overpour Underpinning Cost
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Overpour Underpinning
$350+Per linear foot of underpinned basement foundation. Includes: Demolition, Excavation, Disposal, Forming, Concrete, Call and Pass Building Inspections.
The cost of overpour underpinning in Toronto starts at $350 per linear foot for excavation depths up to 2 feet. When deeper excavation is required (up to 3 feet), the price increases due to additional labour, concrete volume, and extended forming work. This method is generally more affordable than non-shrink underpinning because it does not require a separate grout application day or the use of premium non-shrink materials. Even with the lower cost, overpour underpinning remains a strong and dependable choice for basement lowering projects, offering solid structural support and efficient installation across Toronto homes.
Other basement Underpinning methods
A full-width concrete footing is poured beneath the existing foundation, then allowed to cure for 24–48 hours. After curing, a 2–3 inch gap is filled with non-shrink grout to create a solid, long-term bond between the new footing and the original wall. This is one of Toronto’s most reliable underpinning methods for basement lowering.
The existing footing is partially or entirely removed. A reinforced L-shaped underpinning section is built flush with the original foundation wall and anchored into the footing, allowing the new support to tie directly into the structure. This method keeps the interior walls straight and maximizes usable basement space, making it ideal for narrow or tight layouts.
Bench underpinning is used when digging under the existing footing is not allowed or not safe, such as along party walls without neighbour consent or where an adjacent foundation is too close. Instead of supporting the structure from underneath, this method builds a reinforced concrete bench beside the original footing.
Underpinning basement with us
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- Management & Construction
- Service & Suppor
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Do I need a Permit for Overpour Underpinning?
Yes, a building permit is required for overpour basement underpinning in Toronto. Underpinning changes the structural support of your home, so the city requires architectural drawings, structural engineering plans, zoning verification, and scheduled inspections throughout the project. The permit ensures that all excavation and foundation work follows the Ontario Building Code and is safe for both your home and neighbouring properties. At Strong Basements Inc., we work with trusted engineers to prepare all documents and handle the permit process from start to finish, so your basement lowering project moves forward smoothly and compliantly.
IN TECH HOUSE DESIGN (ITHD) is our trusted architectural and engineering partner, which provides homeowners with zoning bylaws, surveys, design, architecture, engineering, and building permits.
Overpour Underpinning FAQ
What is overpour underpinning?
Overpour underpinning is a method where part of the existing footing is removed and replaced with a wider concrete footing that overlaps the foundation wall. This creates a stronger base and allows the basement floor to be safely lowered.
Why choose the overpour method for basement lowering?
Homeowners choose overpour underpinning because it is fast, cost-efficient, and structurally reliable. It reinforces the foundation while keeping the project timeline short, making it ideal for older Toronto homes that need a quick and safe lowering process.
How much does overpour underpinning cost?
The price for overpour underpinning starts at $350 per linear foot and increases with deeper excavation or more complex site conditions. It is normally the least expensive of all underpinning methods because it requires fewer labour stages and no non-shrink grout.
Is overpour underpinning safe for older homes?
Yes. When completed with proper engineering drawings, staged excavation, and required city inspections, overpour underpinning provides strong and dependable support for older foundations. It is widely used across Toronto for aging homes with shallow basements.
How long does the overpour underpinning process take?
The timeline depends on basement size and excavation depth, but overpour sections are typically installed faster than non-shrink or L-shape methods. Most basements require three sequential stages, with forming and concrete placement completed shortly after each building inspection.
Does overpour underpinning require a building permit?
Yes. All underpinning in Toronto requires a Building Permit, engineered drawings, and staged inspections by both the City and the structural engineer. Overpour underpinning must follow the Ontario Building Code and the approved construction plan.
Can overpour underpinning be used on party walls?
In most cases, yes — but only with neighbour consent. If the neighbouring owner does not grant permission for work under the shared wall, a bench underpinning solution must be used instead.
How does overpour underpinning compare to non-shrink or L-shape methods?
Overpour is the fastest and most economical option. Non-shrink and L-shape methods take longer and use more materials, but may be chosen when the funding shape, site conditions, or engineering design require a different approach.