Why Lot Grading Matters: Preventing Flooding in Calgary Homes

After the devastation of the 2013 flood, Calgary homeowners are no strangers to high waters, but the summer of 2025 has brought the issue into sharp focus once again. With more than 200 millimetres of rain falling across June and July, the city has been saturated, and thousands of residents are facing flooding in Calgary basements. Alberta companies that specialize in foundation repair, waterproofing, and basement drainage have been overwhelmed, with some reporting call volumes more than 300 percent higher than average, surpassing demand from the devastating 2013 floods.

For many homeowners, the immediate concern is mopping up the damage: shop vacuums, towels, and dehumidifiers are flying off store shelves as people scramble to keep mould at bay. But while these emergency fixes are important, the bigger lesson is clear: flood prevention starts outside the home with proper lot grading.

The Link Between Lot Grading and Flooding

Lot grading refers to how the land around your home is shaped and sloped to direct surface water away from your foundation. A properly graded lot prevents water from pooling near the house and reduces the risk of seepage into basements. Without positive lot drainage, heavy rainfall can easily overwhelm foundations, seep through walls, or bubble up through basement slabs, causing costly damage and long-term issues such as mould growth.

The City of Calgary’s Lot Grading Bylaw was designed to ensure that every new residential or commercial property has appropriate surface drainage. The goal is simple but critical: make sure water flows away from buildings and into the city’s drainage system without damaging neighbouring properties or public infrastructure.

When grading is done correctly, water naturally moves toward the street, lane, or swale, protecting both private homes and the broader stormwater system. When it’s done incorrectly — or neglected altogether — the consequences can be severe: basement flooding, property damage, disputes between neighbours, and even stress on Calgary’s public parks, pathways, and underground utilities.

Builder and Homeowner Responsibilities

During the construction of a new home, builders are responsible for establishing lot grades that comply with the bylaw. They must submit an As Constructed Grade Certificate, signed by a professional land surveyor, engineer, or architect, within 12 months of occupancy. This certificate confirms that the lot has been graded to city standards.

However, once construction is complete and the initial grading is approved, responsibility shifts to the property owner. Homeowners are expected to maintain positive lot drainage over the life of their property, which means ensuring that landscaping, patios, decks, or renovations do not disrupt the intended slope of the land.

This is where many Calgarians are caught off guard. Landscaping projects often inadvertently create low spots where water can pool. Over time, soil can settle, altering the original grade. Even small changes can redirect water toward the foundation — and during years like this one, with record-breaking rainfalls, those changes can lead to major flooding problems.

A Critical Update: Limited Monitoring by the City

One of the most important updates in Calgary’s lot grading process is that the City does not actively monitor As Constructed Grade Certificate applications. While the bylaw requires builders to file these certificates, ongoing monitoring and enforcement are limited once construction is finished.

In practice, this means that homeowners cannot assume the City is keeping tabs on the grading of their lot or ensuring ongoing compliance. After the development process wraps up, the City’s role is largely limited to addressing specific bylaw infractions. It does not mediate disputes between neighbours, and it does not monitor changes made to lot grading through landscaping or renovations.

This makes homeowner awareness and vigilance absolutely essential. Flooding prevention isn’t just a matter of municipal oversight — it’s a daily responsibility of property ownership.

The Hidden Costs of Improper Drainage

The rise in flooding-related service calls this summer is a stark reminder of the costs of poor drainage. Water entering through foundation walls, basement slabs, or floor joints doesn’t just damage possessions. It creates conditions for mould growth, which can spread quickly, harm indoor air quality, and pose significant health risks.

Foundation repair and waterproofing services can cost thousands of dollars — and during times of peak demand, even getting a contractor to your home can mean weeks of waiting. By contrast, maintaining positive lot drainage is a relatively low-cost, preventive measure that can save homeowners from major headaches down the road.

Steps for Homeowners to Protect Their Property

So, what can Calgary homeowners do to reduce their flood risk?

• Inspect your grading regularly. Walk around your home after a heavy rain and look for areas where water pools near the foundation.

• Maintain slope away from the house. The land should fall away from the foundation at a minimum slope of 10–15 cm over the first two metres.

• Be careful with landscaping. Adding new patios, walkways, or gardens can change the grade. Always ensure surface water will continue to flow away from your house.

• Ensure concrete swales are unobstructed. Maintain the right-of-way required by concrete swales for proper rainwater drainage.

• Consult professionals when needed. For major grading adjustments or certificate requirements, work with qualified Alberta land surveyors, engineers, or landscapers familiar with Calgary’s bylaws.

The City’s Guide to Lot Drainage is also available to help homeowners, builders, and contractors understand their responsibilities and best practices.

Why Lot Grading Matters More Than Ever

Calgary’s changing climate means heavier rainfalls and wetter summers may become more common. When combined with rapid urban growth, this creates additional strain on the city’s stormwater systems and increases the likelihood of flooding in vulnerable areas.

Lot grading may not seem like a glamorous part of homeownership, but it is one of the most important. Proper grading not only protects individual properties from flooding — it also safeguards neighbourhood infrastructure, reduces disputes between neighbours, and helps ensure that Calgary’s stormwater system can function effectively during extreme weather.

As the events of this summer show, prevention is always better than cure. While the City plays a role in setting bylaws and approving construction, the long-term responsibility falls to homeowners. Staying proactive about lot grading can mean the difference between a dry basement and thousands of dollars in water damage repairs.