Transforming a Leaside Semi-Detached: A Complete Basement Lowering & Underpinning Project in Toronto
When maximizing living space in Toronto’s highly competitive real estate market, converting a shallow, unusable basement into a fully functional living area is one of the smartest investments a property owner can make. Strong Basements Inc. recently partnered with a local realtor and a team of investors to completely transform a property in the Leaside neighbourhood. The goal was to convert a cramped basement into a premium 8-foot-high living space featuring a recreation area, a 3-piece washroom, a laundry room, and a mechanical room. Because the property is a semi-detached home with an older natural stone foundation, this project required highly technical basement underpinning in Toronto and meticulous project management. Here is a behind-the-scenes look at how we executed this complex basement lowering project.Type your paragraph here
The Scope of Work
To deliver the maximum possible square footage and ensure the structural integrity of the home, Strong Basements Inc. provided a comprehensive suite of foundation and waterproofing services:
Sequential Excavation and Underpinning: Digging down and extending the foundation walls to safely lower the basement floor.
Complete Interior Basement Waterproofing: Installing a high-quality dimpled membrane, weeping tile system, and a reliable sump pump.
Underground Drainage System: Roughing in the plumbing for the new 3-piece washroom, laundry drain, and a mechanical room floor drain.
Concrete Floor Construction: Pouring a brand new 4-inch concrete floor over a gravel bed, complete with a 6-mil poly moisture barrier and welded steel wire mesh reinforcement for maximum durability.
Overcoming Unique Leaside Project Challenges
Every older Toronto home has its quirks. Our foundation underpinning contractors navigated several major hurdles on this Leaside property, working closely with the structural engineer to ensure a flawless execution.
1. The Party Wall & Neighbour Relations
In a semi-detached home, your foundation is shared. The elderly neighbours living behind the party wall run a podcast, meaning excessive noise would directly disrupt their daily routine.
The Solution: We handled the legal and administrative heavy lifting, obtaining a separate building permit for the neighbour’s property, securing their letter of consent, and adding them to our underpinning liability insurance as a separate insured party. We also coordinated a strict noise schedule so they could continue streaming their podcasts without interruption. The result? Zero complaints from the neighbours throughout the entire project.
2. Tight Access and Logistics
Like many Toronto properties, the home had extremely limited space on the front driveway for heavy machinery and soil removal.
The Solution: We engineered a custom soil-removal setup, feeding a conveyor belt through a side window. We then utilized smaller, 6-yard soil disposal bins placed carefully in the laneway to keep the site clean and efficient without blocking neighborhood traffic.
3. An Aging Natural Stone Foundation
The original foundation was constructed from natural stone, which can be unpredictable and delicate during excavation.
The Solution: To ensure absolute safety, the structural engineer designed the underpinning in four stages rather than the standard three. While this added one extra week to our timeline for excavation, inspections, concrete pouring, and non-shrink grout application, it guaranteed the structural stability of the century-old stone.
4. Maximizing Space with Flush L-Shape Underpinning
Traditional underpinning often leaves a concrete “bench” around the perimeter, eating into valuable square footage. The investors wanted every possible inch of space.
The Solution: We utilized an L-Shape underpinning method, pouring the new foundation flush with the existing wall. This requires much more complex concrete forms and precision engineering.
5. Custom Liquid Grout for Uneven Stone
Because the bottom of the original stone foundation was incredibly uneven, applying standard non-shrink grout between the new concrete and the old stone would have left dangerous voids.
The Solution: With the engineer’s approval, we sealed the spaces between the new underpinning and the old stone, built custom wells, and poured a high-flowability liquid non-shrink grout. This ensured every single gap and crevice was completely filled and structurally sound.
6. Upgrading a "Time Bomb" Plumbing System
During excavation, we discovered two major plumbing issues. First, the main sanitary line at the exit point was sitting higher than normal, making gravity drainage for the new basement impossible. Second, the home still relied on an outdated clay trap and breather outside.
The Solution: We installed a Liberty Sewaje Ejector System Pro380-Series, widely recognized as the most reliable brand in Ontario, and connected all new basement drainage pipes directly to the ejector pump. We also advised the client to proactively remove the old clay trap. We replaced it with modern, straight PVC piping and back-to-back cleanouts, saving the homeowner from an inevitable future sewage backup.
The Final Result
The project was a resounding success. The structural engineer specifically praised our complex L-shape formwork and our attention to detail with the liquid grout application.
When the client and investors walked the site after our concrete floor construction was complete, they were thrilled with the 8-foot ceiling height, the flawless concrete finish, and the massive increase in usable space. They were so impressed with the performance that Strong Basements Inc. is already slated to handle the underpinning on their next investment property.
We successfully passed the dry, structurally sound, and fully prepped basement over to the finishing renovation team to complete the drywall and fixtures.
Planning a Basement Renovation in Toronto?
If you are looking to increase your basement ceiling height, add a legal basement apartment, or reinforce an aging foundation, you need a contractor who understands the complexities of Toronto’s soil and older homes.Contact Strong Basements Inc. today to discuss your basement lowering and foundation underpinning needs.