Ontario's rainfall patterns are changing. Across the province, short, intense downpours are becoming more frequent, placing stress on building drainage systems that were never designed to handle such volume. For condominium buildings, the result is all too familiar: flooded basements, sump pump failures, backflow into sewer systems, and costly damage to mechanical, electrical and building infrastructure. The need to adapt is no longer a distant concern; it is a pressing reality.

From Climate Data to Design Loads
Designing for the future begins with understanding how the climate is shifting. According to updated climate models and intensity-duration-frequency (IDF) data, Southern Ontario is expected to see a 10% to 20% increase in the intensity of 10-year storms by mid-century. Tools like the IDF_CC allow engineers to project future rainfall patterns and design stormwater systems accordingly. These changes are not minor adjustments; they require fundamental rethinking of how we size, specify and design drainage systems.

Using updated IDF data allows sump pits, roof drains, and storm connections to be designed and built with tomorrow’s storms in mind, not yesterday’s averages.

Drainage Vulnerabilities in Condo Buildings
Most drainage systems in existing condominium buildings were designed using historic rainfall assumptions as per the Ontario Building Code (OBC). In the context of today’s weather, several key vulnerabilities emerge:
•    Sump pits that are too small to accommodate rapid inflows
•    Single sump pumps without redundancy or backup power
•    Improperly installed or inaccessible backwater valves
•    Foundation drains tied into municipal sewers, increasing the risk of surcharge during storm events

During the 2013 Toronto flood, more than 120 mm of rain fell in under two hours. Many buildings experienced widespread flooding not because of catastrophic design flaws, but because systems were simply not built to accommodate and handle that volume in that timeframe.

Sump Pump Systems
An effective sump pump system requires more than just a pump in a pit. Modern design calls for:
•    Dual-pump configurations (duty/standby or duty/assist) to provide redundancy
•    Connection of pumps to building power emergency systems
•    Appropriate sump pit sizing, based on current and future IDF values
•    Check valves and backwater valves to protect against reverse flow. Valves should be installed in a manner that allows testing and future maintenance
•    Water-level sensors and tie-ins to building automation systems for remote alerts

Condominium corporations and property managers should plan on updating outdated stormwater systems as these features reduce the risk of sudden failures and provide building staff with time to act before an event escalates. 

Foundation Drainage & Site-Level Defences
Condominium Corporations can also reduce flood risk by intercepting stormwater before it enters the system. Strategies may include:
•    Redirecting weeping tile systems to dedicated sump pits rather than tying into storm sewers
•    Installing a drainage board and rigid insulation during envelope or waterproofing renewals
•    Improving surface grading and using permeable paving materials to reduce surface runoff
•    Integrating bioswales and rain gardens where site conditions allow

These interventions can often be phased in during other capital projects, reducing incremental costs while improving performance.

Smart Monitoring and Predictive Maintenance
IoT technologies and smart monitoring tools offer new ways to manage drainage infrastructure proactively. High-water alarms, pump cycle analytics, and cloud-based dashboards provide building staff and maintenance teams with real-time data.

Predictive maintenance becomes possible when unusual patterns (such as excessive pump cycles) can be flagged early. This allows staff to investigate minor issues before they become major failures. Maintaining sump pumps and stormwater infrastructure to ensure they are operational during major rainfall events is critical in preventing major flooding. 

Coordination with Municipal Infrastructure
On-site detention systems, including green roofs, cisterns, and controlled-flow roof drains, can reduce the peak discharge into municipal systems. Working with municipalities to understand surcharge zones and infrastructure capacity can help ensure that private upgrades align with broader flood mitigation strategies.

Budgeting & Reserve Fund Planning
Drainage upgrades are a capital investment, but they are also a financial safeguard. By working with engineering consultants to perform lifecycle costing on pumps and drainage equipment, property managers can help strengthen condominium reserve funds to ensure sufficient funds are available for system upgrades. As stormwater infrastructure ages, buildings should plan on upgrading their systems with newer technologies and updated design standards, rather than just replacing existing equipment with similar capacity equipment. 

Conclusion
Climate data makes one thing clear: Ontario’s rainfall patterns are intensifying, and our buildings must adapt. Drainage systems that once met code are now at risk of failure. Proactive engineering, informed by updated data and a whole-system approach, can help property managers and boards safeguard their assets, reduce insurance exposure, and deliver peace of mind to residents.

Resilience does not come from waiting out the storm. It comes from designing for it.

Kaezad Wania is the Vice President of Engineering & Operations at Baypath Inc. With over nine years of experience in building systems engineering, Kaezad has managed and supported numerous condominium corporations through a wide range of projects, including equipment retrofits, building audits, technical investigations, and energy efficiency upgrades.
baypath.ca

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