Strengthening Century Homes: A Guide to Foundation Work in Old Toronto Properties

In this article

There’s a persistent belief among Toronto homeowners that century homes are “too fragile” for foundation strengthening work. The reasoning goes that a house built in 1910 on a rubble stone foundation can’t be touched without risk of destabilizing the whole structure. That belief has delayed necessary work on thousands of GTA homes, sometimes for years, while cracks widened and moisture crept in. It’s not accurate.

Century homes are not more fragile than modern builds. They are different. The foundation materials are different, the construction methods are different, and the soil conditions around them are different. What changes for old Toronto properties is not whether foundation work is possible, but how it has to be planned and executed. This guide covers what that difference looks like in practice.

The myth that slows Toronto homeowners down

The “too fragile to touch” idea comes from a real concern, but applies to a specific subset of cases that contractors sometimes overgeneralize. Rubble stone foundations, which were common in Toronto homes built before 1920, do require a different approach than poured concrete. The stones are not bonded together with modern structural mortar. They’re held by gravity, mass, and the soil pressure against them. Excavating too quickly, removing too much support at once, or failing to account for soil arching can destabilize a rubble wall.

But that describes the risk of bad technique, not the risk inherent in the house. A properly sequenced mass concrete underpinning project on a rubble stone foundation in Riverdale or Cabbagetown is routine work for an experienced contractor. The requirement is that the engineer and contractor understand the specific material, design accordingly, and execute in controlled stages. None of that is impossible. It just can’t be the same sequence as work on a poured concrete foundation in a 1980s North York home.

What makes century home foundations different

Before any foundation work can be planned, the structural engineer and contractor need a clear picture of what they’re working with. Three things differ most significantly from modern foundations.

Foundation material

Pre-1920 Toronto homes typically have rubble stone or early brick foundations. Homes from 1920 to 1950 often have hollow tile, unreinforced concrete block, or early poured concrete of variable quality. Homes from 1950 to 1970 may have reinforced poured concrete, though the reinforcement standards were lower than today. Each of these materials has different load distribution characteristics, different behaviour under stress, and different compatibility with the new concrete that an underpinning contractor will pour.

Foundation depth

Century homes were often built with shallow foundations, sometimes as little as 3 to 4 feet deep, compared to the 7 to 8 foot depth standard today. That shallow depth is precisely why so many Toronto homeowners want to underpin: to gain usable basement height. But it also means the original foundation has been carrying the load of the house at a depth with less soil bearing capacity than modern standards would require. A structural engineer needs to confirm that the underpinning plan will transfer load to competent soil, not just to the same stratum the original foundation was resting on.

Adjacent properties

Toronto’s older residential neighbourhoods are characterized by houses with very little separation. Semi-detached houses share a foundation wall. Detached houses may have 3 to 6 feet between them. When you excavate alongside a shallow foundation to underpin it, the adjacent property’s foundation is exposed to the same soil movement risks. A party wall agreement, the structural engineer’s design for shoring, and proper sequencing to maintain soil support are non-negotiable in these conditions. The City of Toronto’s Building Division has specific requirements for this documentation.

Step 1: Structural assessment and soil report

No responsible contractor will give you a meaningful quote for old house foundation work without a structural assessment first. Any contractor who quotes based on a walk-through of the basement without an engineer’s report is either underquoting and will revise significantly once they start, or is underqualified for the work.

What the assessment should include:

• Foundation type and condition – the engineer documents the material, visible defects, any evidence of prior movement, moisture damage, and the estimated remaining structural life
• Soil bearing capacity – for homes in clay-heavy areas of the GTA, the bearing capacity of the soil at the proposed new footing depth is critical. Clay can compress, especially if it’s been previously disturbed
• Adjacent structure conditions – if shared walls or tight adjacency is involved, the engineer documents the neighbouring foundation condition as part of the design for shoring
• Proposed new depth – confirms the depth needed to reach bearing soil and the headroom that will result after the work is complete

Structural engineering fees for a Toronto residential foundation assessment range from $1,500 to $4,000 depending on scope and complexity. That cost is essential, not optional, and usually saves more than it costs by identifying conditions that would have caused surprises mid-project.

Step 2: Permit and party wall agreement

Foundation work in Toronto requires a building permit from the City of Toronto’s Building Division. The permit process for a century home typically requires stamped structural drawings from a Professional Engineer registered in Ontario. For work adjacent to a shared wall, a party wall agreement with the neighbouring property owner must be executed before work starts.

The permit process takes 4 to 12 weeks for residential foundation work depending on the volume of applications and the completeness of the submission. Planning this lead time into your project schedule is not optional. Starting work without a permit creates liability under the Ontario Building Code and can result in a stop-work order that leaves your foundation mid-excavation.

Step 3: Choosing the right underpinning method

There are several foundation underpinning methods used in Toronto, and the right one depends on the foundation type and the soil conditions identified in step 1.

Mass concrete underpinning (pit method)

The most common method for residential Toronto projects. The excavation is done in alternating sections (pins), never the full length at once, to maintain soil support under the existing foundation at all times. Each section is dug, formed, inspected, and poured before the adjacent section is opened. This is the right method for most century homes because it works with gravity and soil arching rather than against them. It’s labour intensive and the most time-consuming option, but it’s also the most predictable for variable foundation conditions.

Screw pile supplementation

Screw piles are helical steel piles drilled to bearing depth and then connected to a new grade beam that supports the existing foundation. This is used when soil conditions are too unpredictable for mass concrete, when vibration from conventional excavation is a concern for adjacent structures, or when the project scope requires maximum headroom gain without the time cost of pin underpinning. Equipment access is a limiting factor in tight urban lots.

Benching (bench footing)

Rather than excavating directly under the existing footing, a benching system creates a stepped footing structure that widens out from the existing foundation base. This is generally less expensive than full underpinning but does not provide as much headroom gain and is not suitable for foundations with poor structural condition. It’s sometimes appropriate for century homes when the goal is waterproofing and modest headroom improvement rather than maximum depth increase.

Step 4: Waterproofing during the dig

Any foundation project that exposes the exterior of the foundation wall is an opportunity to apply exterior waterproofing. This is one of the strongest arguments for doing exterior waterproofing at the same time as foundation depth work: the excavation cost is already there. Adding waterproofing membrane application, new drainage board, and fresh weeping tile at footing level during an underpinning project adds modest cost to a job where the major cost driver (excavation and shoring) is already paid for.

For century homes with rubble stone or early brick foundations, exterior waterproofing applied during the underpinning dig often solves decades of basement moisture problems in one project. The combination is increasingly the norm among Toronto homeowners who understand the sequencing benefit.

Step 5: Finishing the new foundation

Once the underpinning concrete has cured to the specified strength (typically 28 days for full cure, though work can often proceed after 7 days), the new basement floor can be poured at the new elevation. This is also when interior drainage systems, if included, are installed before the floor is poured. The floor and wall systems are tied together, inspections are completed, and the project moves to framing if a full basement conversion is planned.

Finishing a century home basement after foundation work requires attention to the older building envelope above. Wall insulation, vapour barrier placement, and window well drainage all need to be coordinated with the new basement conditions. A basement that previously had minimal moisture issues can develop new ones if the new floor is poured without considering where condensation will form against the old above-grade walls.

What it costs in Toronto

Foundation work on a century home in Toronto varies significantly with scope, but these are the reference ranges contractors work within for 2026.

These numbers assume reasonable site access and straightforward soil conditions. Rocky ground, very tight adjacency to a neighbouring foundation, or unexpected utility conflicts can increase costs significantly. The structural assessment in step 1 is designed to surface these variables before the contractor is committed to a fixed price.

For a project-specific estimate for your Toronto century home, contact Icy Reno Waterproofing. They operate throughout the GTA including older residential areas in Toronto’s east and west ends, North York, and Etobicoke.

Frequently asked questions

All costs listed are general estimates intended for informational purposes and are subject to change based on market conditions. Actual pricing will vary significantly depending on your home’s unique infrastructure, chosen equipment, and current local labor rates. We recommend obtaining a detailed quote from a licensed professional for an accurate assessment of your specific project.