Large Detached Deep Lowering Project in Erin Mills, Mississauga
Deep lowering for a legal duplex conversion required the maximum allowable depth under local soil-bearing capacity and continuous engineering oversight. Completed by Toronto Basement Underpinning in August 2024. Fixed-price contract, engineered drawings and Peel Region permit coordination included.
- Delivered on time and within budget
- 9.9/10
- Total project cost
- $75,000
- Local labor
- 80%
- Local supplier spend
- 100%
- Basement size
- 1,420 sqft
- New area gained
- 1,180 sqft
- Linear footage underpinned
- 180 lin ft
- Pins poured
- 32
- Depth gain
- 2'10"
- Original ceiling
- 5'2"
- Finished ceiling
- 8'0"
- Client
- Homeowner in Mississauga
- Completion
- August 2024
- Location
- Erin Mills, Mississauga, ON
- Sector
- Residential
- Permit turnaround
- 10 weeks
- Warranty
- 10 years
Introduction
Deep lowering for a legal duplex conversion required the maximum allowable depth under local soil-bearing capacity and continuous engineering oversight. The property is a residential detached in Erin Mills, Mississauga, with an original 5'2" basement ceiling across a 1,420 sqft footprint. Our crews delivered a full perimeter deep lowering for legal duplex project under a fixed-price contract that bundled engineered drawings, Peel Region permit coordination, excavation, pin-by-pin underpinning, interior waterproofing, and new slab pour.
The scope lowered the basement by 2'10" to deliver a 8'0" finished ceiling across 1,180 sqft of newly usable standing-height basement area, directly enabling the homeowner's plan for a legal secondary use of the lower level.
The Underpinning Process
A controlled sequence of engineered steps delivered the Erin Mills project on time and within budget. Each phase passed Peel Region inspection before the next began.
1. Deep Assessment and Full Engineering
Deep-lowering projects require geotechnical confirmation of soil-bearing capacity to the target footing depth, written structural engineering sign-off, and settlement monitoring plan filed with the municipality before mobilisation.
2. Excavation
Pin-by-pin excavation along 180 linear feet of perimeter to 2.83 feet below the original slab. Strict alternating segment sequence to maintain continuous support.
3. Underpinning Pits
Mass-poured concrete footings at the maximum depth allowed by the soil assessment, each pit confirmed by the structural engineer before pour.
4. Steel Reinforcement
Heavy 15M rebar cages with additional lateral ties for deep-column load transfer. Vertical dowels tied into the retained upper footing.
5. Structural Supports and Settlement Monitoring
Full-structure monitoring instrumentation installed and read daily. Settlement maintained within engineered tolerances throughout the six-week on-site phase.
6. Waterproofing and Drainage
Full perimeter interior Delta-MS, perforated weeping tile, dual sump pits with battery backup, and backwater valve installation on the main sewer connection.
7. Insulation and Finishing
New engineered slab poured over vapor barrier. Basement now has an 8-foot standing ceiling across the full 1,180 sqft of new living area, ready for legal duplex finishing trades.
Our Approach
Delivered on time and within budget. The Erin Mills project ran through several site challenges: lakeside port credit and cooksville sit on heavy lake iroquois clay that drives foundation settlement, while erin mills subdivisions built in the 1980s used engineered fill with more predictable underpinning conditions. We addressed each early by sourcing locally where material shortages hit, scheduling around weather windows, and running hydraulic jacks plus specialised concrete mixes during the deepest excavation phase. Modern waterproofing membranes replaced the aging drainage components, and the result is a basement that is both structurally sound and dry.
What's Included in This Project Scope
The fixed-price contract covered every item below. No line-item surprises, no change orders unless the homeowner added scope. One contract, one warranty, one crew.
- Deep-lowering geotechnical soil-bearing capacity assessment
- Full engineering package with settlement monitoring plan
- City permit application and inspection coordination
- Pin-by-pin excavation to maximum engineered depth
- Mass-poured concrete footings with engineer sign-off per pit
- Heavy 15M rebar cages with additional lateral ties
- Full-structure monitoring instrumentation with daily reads
- Full interior perimeter Delta-MS and perforated weeping tile
- Dual sump pits with battery backup and backwater valve
- Engineered reinforced slab pour over vapor barrier
- Workmanship warranty on all structural work
Social Impact
Local engineer, local structural monitoring, local waste-haul trades, and 100% of structural materials sourced from Ontario suppliers. Reduced project transport footprint by an estimated 400 vehicle miles compared to an out-of-city crew.
Client Testimonials
Rated 4.9 stars across projects documented on the site.
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Thinking About Underpinning in Mississauga?
Every project on this site is delivered on a fixed-price contract with engineered drawings, Peel Region permits, and a workmanship warranty included. The scope of your project may differ from this one - we size the quote to your actual building, soil, and depth-gain goal. Book a free site assessment and we respond within two business hours.