How do I fix a depression after winter on my Ottawa driveway?

Depressions that appear after winter on Ottawa driveways are typically caused by base settlement, frost heaving, or water infiltration that weakened the foundation layers during freeze-thaw cycles. The repair method depends on the size, depth, and underlying cause of the depression.

Small depressions (less than 1 square metre, under 25mm deep) can often be addressed with cold patch asphalt as a temporary fix, followed by hot-mix patching in warmer weather. Clean out any loose material, apply cold patch slightly above the surrounding surface level, and compact with a hand tamper or drive over it repeatedly. However, cold patch rarely lasts more than one Ottawa winter season, so plan for a permanent hot-mix repair when temperatures consistently stay above 10 degrees Celsius.

Larger or deeper depressions indicate base failure — the most common cause in Ottawa due to our extreme freeze-thaw cycles and deep frost penetration. When water infiltrates through cracks or porous asphalt, it reaches the granular base and subgrade. During Ottawa's 50+ annual freeze-thaw cycles, this water expands and contracts, gradually washing out fine base materials and creating voids. The asphalt surface then settles into these voids, creating the depression you see.

For permanent repair of significant depressions, the affected area must be cut out completely, excavated to stable base, and rebuilt from the bottom up. This means removing the failed asphalt, digging out compromised base material (often 300-600mm deep), placing fresh Granular B and Granular A base in compacted lifts, and installing new hot-mix asphalt. Professional repair typically costs $15-25 per square foot depending on depth and access.

Ottawa's clay soils compound the problem — prevalent in Barrhaven, Orleans, Gloucester, and Riverside South. Clay expands when wet and shrinks when dry, creating unstable subgrade conditions. If your depression keeps returning after repairs, the subgrade may need geotextile fabric and additional base depth to prevent clay migration and provide stable support.

Timing matters critically in Ottawa. Hot-mix asphalt repairs should wait until ambient temperatures are consistently above 10 degrees Celsius (typically late May through September). Asphalt placed in cool conditions won't compact properly and will fail again within a season. If the depression is creating a safety hazard or water pooling issue, use cold patch temporarily but plan for proper hot-mix repair during paving season.

Prevention is key — depressions often start as small cracks that allow water infiltration. Regular sealcoating every 2-3 years and immediate crack filling prevent water from reaching the base layers. Once water penetrates to the base in Ottawa's climate, freeze-thaw damage accelerates rapidly.

When to hire a professional: Any depression larger than 2 square metres, deeper than 50mm, or that keeps returning after DIY repairs indicates structural base failure requiring excavation and rebuilding. Professional contractors have the equipment to properly compact base materials and place hot-mix asphalt at correct temperatures.

Need help finding a driveway contractor? Ottawa Driveways can match you with local paving professionals for a free estimate on permanent depression repair.