How does the City of Toronto's mandatory downspout disconnection affect basement waterproofing?

The City of Toronto's mandatory downspout disconnection bylaw, enacted in 2011, requires all residential downspouts to be disconnected from the city's sewer system and redirected to discharge onto your property's surface — and while this reduces strain on the sewer system and lowers the risk of basement sewer backups across the city, it can actually increase the risk of water infiltration into your specific basement if the discharged water is not properly managed. Understanding this tradeoff is essential for any GTA homeowner planning a basement renovation.

Before the bylaw, most Toronto homes had downspouts connected directly to the storm sewer or combined sewer through underground pipes. This meant roof runoff went straight into the sewer, away from your foundation. The problem was systemic — during heavy rainstorms, millions of litres of roof runoff overwhelmed the combined sewers (which carry both stormwater and sanitary waste in older Toronto neighbourhoods), causing sewage to back up into basements across the city. The downspout disconnection bylaw addresses this by keeping roof runoff out of the sewer system entirely.

The consequence for individual homeowners is that all that roof water — thousands of litres per storm for a typical Toronto home — now discharges at ground level around the perimeter of your home, exactly where your foundation meets the soil. If the water is not directed away from the foundation with proper grading, splash pads, or downspout extensions, it soaks into the soil directly adjacent to your foundation walls, increasing hydrostatic pressure and driving water toward any crack, gap, or failing section of your weeping tile system. In the clay-heavy soils found throughout much of Toronto, Scarborough, North York, and Mississauga, this water does not percolate downward quickly — it sits against the foundation, expanding the clay and exerting lateral pressure on the walls.

Proper downspout discharge management is now a critical component of basement waterproofing in the GTA. Every disconnected downspout should discharge onto a splash pad (a concrete or plastic pad that directs water away from the foundation) and the water should flow at least 6 feet away from the foundation wall before reaching permeable ground. Flexible downspout extensions that unroll during rain and retract in dry weather are an inexpensive ($10-$25 each) and effective solution. For properties where space is tight — common in Toronto's older neighbourhoods with narrow side yards — a rain barrel ($40-$80, or often available free or subsidized through the City of Toronto's environmental programs) captures downspout discharge and releases it slowly through a garden hose or drip irrigation, preventing the concentrated surge of water against the foundation.

Grading around your foundation must slope away from the house at a minimum of 2% grade (roughly a 1-inch drop per foot) for at least the first 6 feet. Many older Toronto homes have experienced settlement and landscaping changes over decades that have reversed this grade, creating depressions that funnel water toward the foundation rather than away from it. Before finishing your basement, walk the exterior perimeter during a rainstorm and observe where water flows. Correcting grading issues is relatively inexpensive ($500-$2,000 for regrading around the perimeter) and can be the difference between a dry basement and a flooded one.

If you are planning a basement renovation, address your downspout discharge as part of your waterproofing strategy. The combination of properly disconnected and extended downspouts, correct grading away from the foundation, functioning weeping tile, a sump pump with battery backup, and a backwater valve on the sanitary sewer creates a comprehensive water management system. Neglecting any single element can undermine the others. Toronto Basement Remodeling can help you find a waterproofing professional through the Toronto Construction Network who can assess your specific situation and recommend the right combination of measures for your home.