What's the base depth for an Ottawa interlock driveway?

Interlock driveways in Ottawa require a minimum total base depth of 450mm (18 inches) due to our extreme frost conditions — significantly deeper than southern Ontario requirements.

The proper base structure for an Ottawa interlock driveway consists of three critical layers. First, you need 300mm (12 inches) of compacted Granular B sub-base, which is coarse crushed stone ranging from 100mm down to dust. This layer must extend below Ottawa's frost line of 1.2 to 1.5 metres in critical areas and provides the primary structural foundation. Above that, you need 150mm (6 inches) of compacted Granular A base, which is finer crushed stone (25mm to dust) that creates a stable, level platform. Finally, there's 25-50mm of bedding sand where the pavers are actually set.

Ottawa's brutal freeze-thaw conditions make adequate base depth non-negotiable. Our region experiences over 50 freeze-thaw cycles per winter, and temperatures swing from -30°C to +35°C throughout the year. This massive temperature differential causes the ground to heave and settle repeatedly. An interlock driveway with insufficient base depth — say, only 300mm total — will show settling, shifting, and individual paver displacement within the first winter. The pavers themselves aren't the problem; it's the inadequate foundation beneath them.

On Ottawa's prevalent clay soils (common in Barrhaven, Orleans, Gloucester, and Riverside South), you'll often need geotextile fabric between the excavated subgrade and the Granular B layer. Clay expands when wet and shrinks when dry, creating unstable conditions that can migrate into your granular base and compromise the entire structure. Sandy soils in areas like west Kanata and Stittsville drain better but may still require fabric to prevent base migration.

Each base layer must be compacted in lifts using a plate compactor or vibratory roller. You cannot simply dump 450mm of material and compact it all at once — the bottom layers won't achieve proper density. Granular B should be placed and compacted in 150mm lifts, followed by the Granular A in a single 150mm lift. Proper compaction is what prevents settling and maintains the precise levels needed for good drainage.

Budget contractors sometimes try to cut base depth to save money, but this is catastrophic in Ottawa's climate. The few hundred dollars saved on granular material leads to thousands in repair costs when the driveway fails within 2-3 years. Quality interlock installation with proper base depth costs $12-22 per square foot in Ottawa, but it lasts 25-30+ years with basic maintenance.

When to hire a professional: Interlock base preparation requires precise excavation, proper slope grading for drainage, and specialized compaction equipment. This isn't a DIY project — improper base work destroys the entire driveway investment.

Need help finding a qualified interlock contractor? Ottawa Driveways can match you with experienced local professionals who understand Ottawa's specific base requirements.