4 Methods of Lowering a Basement Floor in Toronto: What Homeowners Need to Know

Lowering a basement floor in Toronto requires careful planning, structural design, and the right method of foundation support. Every property is different, so the approach must match the condition of the foundation, the layout of the house, and the depth required for the new basement height.

At Strong Basements Inc., we use four proven methods for lowering basements in Toronto and the GTA:

• Non-Shrink Underpinning
• Overpour Underpinning
• L-Shape (Flush-With-Wall) Underpinning
• Bench Underpinning

Each method has its purpose, and understanding the differences helps homeowners know what to expect during their basement lowering project.

1. Non-Shrink Underpinning

Non-shrink underpinning is the standard method used in most residential basement lowering projects. The crew excavates a section under the existing footing, pours a new concrete base the full width of the original footing, and leaves a small gap between the two. That gap is later filled with non-shrink grout, which bonds the new footing to the old foundation without settlement.

This method is reliable, widely approved by Toronto engineers, and works well for homes with typical soil conditions and standard foundation walls.

2. Overpour Underpinning

The overpour method is used when the project requires the new footing to overlap the existing wall. After excavation, a portion of the old footing is removed, and the concrete is poured so that it ties directly into the wall above. A concrete vibrator is used to eliminate air pockets and create a solid connection.

This method provides strong load transfer and is often chosen when the house needs extra structural support or when the existing footing is irregular or deteriorated.

3. L-Shape Underpinning (Flush-With-Wall)

The L-shape method is used when the design requires the new footing to be flush with the interior wall. The excavation forms an L-shaped pocket: narrow at the top and wider at the base to match the width of the original footing. The new concrete section is reinforced with rebar and tied into the wall with metal anchors.

This method is ideal where the interior layout needs straight walls without inward concrete projections, such as for finished basements, framing, or interior design requirements.

4. Bench Underpinning

Bench underpinning is used when it is not possible or not permitted to excavate under the existing footing. Instead of digging under the wall, a new raised “bench” of concrete is built inside the basement, supporting the new lowered floor.

Bench systems are commonly used in situations such as:

• The neighbour’s footing is too close to excavate safely
• Semi-detached homes where the neighbour does not allow underpinning of the shared wall
• Foundations that are not structurally suitable for traditional underpinning

While the bench creates a visible ledge along one or more walls, it enables deeper excavation safely when regular underpinning cannot be done.

Choosing the Right Method for Your Toronto Home

Each basement lowering project in Toronto is unique. Soil depth, foundation type, structural loads, and property boundaries all determine which method is appropriate. A structural engineer designs the underpinning plan, and the contractor follows the plan in stages to keep the house stable throughout the work.