How deep should the base be for an interlock driveway in Ontario?

Driveways commonly use about 8 to 12 inches of compacted granular base, while walkways and patios typically use 4 to 6 inches. Weak or wet clay soils may need more. A quote with only 4 inches of base under a driveway is a red flag.

What gravel is used under interlocking pavers in Ontario?

Granular A, a crushed limestone base, is the standard base material under interlock in Ontario. Ontario's provincial specification OPSS 355 calls for Granular A base and Granular B subbase, both compacted.

Why do interlock driveways sink or heave?

Sinking and heaving usually come from too little base, base that wasn't compacted in thin layers, poor drainage, or missing edge restraints. Freeze-thaw cycles exploit every weak spot.

Is interlock better than concrete in Ontario winters?

Interlock flexes with ground movement and individual pavers can be lifted and reset, so it tends to handle freeze-thaw better than a single concrete slab that can crack. Both need a solid, well-drained base.

When is the best time to install interlock in London, Ontario?

Interlock can be installed whenever the ground isn't frozen or saturated, typically spring through late fall in Southwestern Ontario.

Interlock Driveways and Patios in London, Ontario: Base Prep That Survives Freeze-Thaw

Kayden Stone

Oct 4

4 min read

A beautiful interlock driveway or patio can last decades in Southwestern Ontario, or start sinking, shifting and growing weeds after a couple of winters. The difference almost never comes down to the pavers. It comes down to what's underneath them. This guide explains how interlock should be built to survive London, Ontario freeze-thaw cycles, and what to ask before you sign a quote.

Why base prep matters so much in London, Ontario

Our winters freeze and thaw the ground over and over. Water trapped in fine, clay-rich soil expands when it freezes and lifts whatever is on top. A deep, well-compacted, free-draining base gives that water somewhere to go and spreads loads so the surface stays flat.

The goal of the base isn't to dig below the frost line. Interlock is a flexible pavement: the joints let pavers move slightly and settle back without cracking. The base just has to be thick enough, compacted enough and drained well enough that movement stays small and even.

The anatomy of a proper interlock installation

Excavation to the right depth, with the subgrade shaped to slope away from buildings.
Subgrade compaction and, on soft clay, a geotextile fabric to keep soil from mixing into the base.
Granular base placed and compacted in thin lifts.
Bedding sand, about 1 inch, screeded smooth.
Pavers laid in the chosen pattern.
Edge restraint to lock the perimeter.
Joint sand, often polymeric, swept in and compacted.

How deep should the base be?

Walkways and patios: typically 4 to 6 inches of compacted base, according to a widely used paver installation guide.
Driveways: typically 8 to 12 inches of compacted base, with more on weak or wet soils.
Total excavation depth adds the paver thickness and bedding sand on top of that.

One frost-region paver supplier puts it bluntly: if one contractor proposes a 4-inch base under a driveway while others are at 8 to 10 inches, that's a red flag.

What material goes underneath: Granular A

In Ontario, Granular A crushed limestone is the standard base under interlock. The province's own specification for installing interlocking concrete pavers, OPSS 355, calls for Granular A base over Granular B subbase, both compacted. Industry guidance recommends placing base in compacted layers of roughly 2 to 3 inches, not dumping it all in at once.

Broken and shifted paving stones caused by poor base preparation and frost heave

Drainage: the silent killer of interlock

Slope the surface away from the house. Patios and driveways should shed water toward lawn, swales or drains, not your foundation.
Don't trap water. On clay, a patio built in a low spot becomes a bathtub. Sometimes a French drain or catch basin needs to go in first.
Mind your downspouts. Don't let roof water dump onto pavers and undermine edges. London's Drainage By-law WM-4 requires downspouts to discharge at least 0.7 m from the building.

Edge restraints and joint sand

Without a solid edge, pavers slowly creep outward and joints open up, letting sand wash out and weeds move in. A proper edge restraint is non-negotiable on driveways. Polymeric joint sand hardens after watering to help resist washout, ants and weeds.

Warning signs your interlock was built wrong

Ruts in the driveway where tires run
Pavers rocking or sitting at different heights
Edges spreading into the lawn
Puddles that sit on the surface after rain
Sand washing out of joints every spring

In many cases we can lift the pavers, rebuild the base and relay the same stones, which saves money over buying new material.

Planning your project

Locates first. Free utility locates through Ontario One Call are required before digging.
City property. Work that affects the City boulevard or a curb cut may need approval through the City of London's Work Approval Permits process.
Think about grading as a whole. A new patio changes how water moves. Our guide to lot grading in London explains how to keep water flowing the right way.
After a pool removal? If you want a patio where the pool used to be, tell us before backfill so we can place and compact the right material. See pool removal costs.

Questions to ask any interlock contractor

How deep will the compacted base be, and what material?
How thick are your compaction lifts?
Will you use geotextile on our clay subgrade?
What edge restraint will you use?
How will the surface drain?
Do you carry WSIB coverage and liability insurance?

Frequently asked questions

How long does an interlock driveway last?

With a proper base and drainage, decades. Individual pavers can be replaced if damaged.

Can interlock be installed over an old asphalt driveway?

Not usually. The old surface and base are typically removed so a proper granular base can be built.

Will weeds grow between pavers?

Some may, but polymeric sand and a dense pattern reduce them a lot.

Does SPM install interlock?

Yes. We handle excavation, base, pavers and finishing grading and sod around the new hardscape.

Get a free interlock quote

SPM Landscape & Excavation is WSIB covered with $1M liability insurance and has served London and Southwestern Ontario since 2006. Call or text (519) 474-0008 or browse our services.

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