How do I repair a sunken section in my Ottawa asphalt driveway?

A sunken section in your asphalt driveway indicates base failure beneath the surface, and proper repair requires excavating the affected area, rebuilding the base, and repaving — this is not a surface-level fix that sealcoating or patching can address.

The sunken area developed because the granular base beneath your asphalt has either washed out, settled due to poor compaction, or been compromised by water infiltration. In Ottawa's freeze-thaw climate, water penetrates through cracks in the asphalt surface, saturates the base material, and creates voids when it freezes and expands. Over repeated freeze-thaw cycles, the base loses its structural integrity and can no longer support the asphalt surface above, causing the visible depression.

Proper repair involves complete reconstruction of the affected area. The sunken asphalt must be cut out with a concrete saw in clean, straight lines extending at least 300mm beyond the visible damage. The failed base material is excavated to stable subgrade — often 450mm to 600mm deep in Ottawa due to our 1.2 to 1.5-metre frost line. Fresh Granular B sub-base is placed and compacted in 150mm lifts, followed by Granular A base, also compacted properly. Finally, new hot-mix asphalt is placed to match the existing surface thickness, typically 75mm to 100mm total in two lifts.

Why surface fixes fail in Ottawa: Simply filling the depression with cold patch or adding a thin overlay of hot-mix asphalt over the sunken area will fail within one winter. The underlying base instability remains, and Ottawa's extreme freeze-thaw cycling will quickly break through any surface repair. Cold patch is particularly unsuitable — it's designed for temporary repairs and loosens completely after 10 to 20 freeze-thaw cycles.

Cost expectations for proper repair: Reconstructing a sunken section typically costs $15 to $25 per square foot, depending on the depth of excavation required and access for equipment. A typical car-sized sunken area (3m x 3m) runs $1,350 to $2,250 for complete reconstruction. This seems expensive compared to a $50 bag of cold patch, but proper repair lasts 20+ years while surface patches fail every winter.

When to tackle the entire driveway: If your driveway has multiple sunken areas, extensive cracking, or is over 15 years old, full replacement often makes more economic sense than piecemeal repairs. Ottawa's climate is particularly hard on driveways with compromised drainage or inadequate original base preparation.

This is definitely professional work. Base reconstruction requires excavation equipment, proper granular materials, compaction equipment, and hot-mix asphalt placement with a paver and roller. The repair must tie into the existing driveway seamlessly and maintain proper drainage slopes.

Need help finding a driveway contractor? Ottawa Driveways can match you with local paving professionals who understand Ottawa's soil conditions and climate requirements for lasting repairs.