Non-Shrink Underpinning
Professional Foundation Support for Basement Lowering
Non-shrink underpinning is one of the safest engineered methods, especially for older homes where the existing foundation needs a stronger footing before deeper excavation, waterproofing, drainage upgrades, and installation of a new concrete slab.
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What Is Non-Shrink Underpinning?
Non-shrink underpinning is a foundation-reinforcement method where a new full-width concrete footing is poured directly beneath the existing foundation wall. After the concrete cures, a 2–3 inch gap between the new footing and the old foundation is filled with non-shrink grout, creating a solid structural bond.
This technique is widely used in Toronto because it provides stable support, predictable performance, and reliable long-term results for basement lowering projects.
Non-Shrink Underpinning Process
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.
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.
A structural engineer inspects soil conditions, footing preparation, and excavation depth to confirm compliance with the engineering plan and the Ontario Building Code.
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.
Once the concrete has cured, the 2–3 inch gap between the new footing and the original foundation wall is filled using non-shrink grout.
The grout is prepared by adding a small amount of water, enough to make the mix moist and firm, similar to packed sand on a beach.
The grout is packed into the gap and compacted by hand, using a hammer and a 2×4 wood board.This method forces the material into every space and makes the grout dense, tight, and almost rock-solid once cured.
This creates a strong connection between the old foundation and the new concrete footing.
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, and then followed by the same non-shrink grout installation process.
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.
The last underpinning sections are poured, vibrated, cured, and finished with non-shrink grout. Once all stages are complete, the basement is ready for interior waterproofing, drainage work, and installation of the new concrete slab.
Non-Shrink Underpinning Cost
The cost of non-shrink underpinning in Toronto starts at $380 per linear foot for excavation depths up to 2 feet. When deeper excavation is required — up to 3 feet — the price increases to $420+ per linear foot due to additional labour and materials. This method is typically more expensive than the overpour approach because each stage requires an extra day of work to install and compact the non-shrink grout, and the grout itself is a premium material. Despite the higher cost, non-shrink underpinning provides one of the strongest and most reliable structural connections for basement lowering projects.
Other basement Underpinning methods
Part of the original footing is removed, and new concrete is poured to overlap the foundation wall, creating a wider and stronger structural base. The concrete is placed using a concrete vibrator to ensure full settlement and to eliminate air bubbles, improving strength and long-term performance. This is the fastest and most efficient underpinning method for older Toronto homes.
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.
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Do I need a Permit for Non-Shrink Underpinning?
Yes, a building permit is required for 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.
Non-Shrink Underpinning FAQ
Non-shrink underpinning is a method where a new full-width concrete footing is poured under the existing foundation, leaving a 2–3 inch gap that is later filled with non-shrink grout. This creates a solid, long-term bond between the old foundation and the new footing, making it one of the safest options for basement lowering in Toronto.
Homeowners choose non-shrink underpinning because it offers a stronger and more stable foundation connection than standard concrete alone. The grout used in this method does not shrink as it cures, which helps prevent settlement and improves long-term structural performance. It is especially recommended for older Toronto homes that require added support before lowering the basement floor.
Non-shrink underpinning typically starts at $380 per linear foot, with deeper excavation up to three feet costing $420+ per linear foot. This method is slightly more expensive than overpour underpinning because it requires an extra day of labour per stage and uses a special grout mix that is more costly than standard materials.
The timeline depends on basement size and the number of underpinning sections, but non-shrink underpinning generally takes 2–4 weeks. Each stage requires 24–48 hours of concrete curing, followed by the application and compaction of non-shrink grout. This additional step adds time but provides a much stronger structural connection.
Yes. Non-shrink underpinning is considered one of the safest engineered underpinning methods because the grout creates a tight and stable bond between the new footing and the existing foundation wall. When built with engineered drawings, proper inspections, and qualified contractors, it provides excellent support for basement lowering, waterproofing upgrades, and new concrete slab installation.