Most residential interlocking in the GTA needs 8 to 10 inches of compacted granular base, and heavy clay properties across Mississauga, Brampton, and parts of Markham often need 10 to 12 inches plus geotextile fabric. That's the direct answer. The longer answer is why: base work typically eats up roughly a quarter to a third of what you pay for an interlocking project, it's completely invisible once the pavers go down, and it's the single variable that decides whether your driveway lasts 7 years or 35. This guide walks through exactly what's under a properly built interlocking surface, how deep it actually needs to be for your soil and application, and the materials and compaction standards that separate a base that lasts decades from one that quietly fails.
Quick answer — what's under a properly built interlocking surface
A correctly built interlocking base, from the native soil up, looks like this: the native subgrade, geotextile fabric on clay soils, 8 to 12+ inches of compacted granular base material laid and compacted in lifts, a roughly 1-inch bedding sand setting layer, the pavers themselves, and polymeric sand swept into the joints. Every layer has a specific job. Skip or thin out any one of them and the surface above it, no matter how good the pavers are, is working on borrowed time.
This is also why two interlocking quotes that look similar on paper can age completely differently. The paver itself usually accounts for only 18 to 28% of the installed cost, which means the gap between a $14,000 quote and a $25,000 quote for the same standard two-car driveway almost always lives in what's happening below grade, not in the stone on top.
The full base assembly, layer by layer
Every properly built interlocking surface, driveway or patio, is a stack of distinct layers, each doing a job the others can't.
1. Native subgrade
The soil that was there before the project started, excavated to the correct depth and, critically, with all organic material (topsoil, roots, old sod) removed. Organic material decomposes over time and creates voids, which is a guaranteed future low spot no matter what goes on top of it.
2. Geotextile fabric (on clay soils)
A permeable fabric membrane laid directly over the native subgrade before any base material goes in. Its job is to stop the granular base above and the clay subgrade below from mixing. Without it, fine clay particles migrate upward into the base over repeated freeze-thaw cycles and vehicle load, clogging the base's ability to drain and accelerating settlement from underneath. Across the heavy clay soil common through much of Mississauga, Brampton, and parts of Markham, this is a standard layer, not an upsell.
3. Compacted granular base
The structural layer that does the real work: 8 to 12+ inches (see the depth breakdown below) of crushed stone, compacted in layers rather than dumped and compacted all at once. This is what actually bears the load, resists frost movement, and keeps the surface flat for decades. It's also where the bulk of a properly quoted project's hidden cost lives.
4. Bedding sand
A thin, roughly 1-inch setting bed of coarse, washed bedding sand laid and screeded flat on top of the compacted granular base. This is a specific material, not generic sand, and its only job is to give each paver a stable, even, consistent surface to sit on. It is not the same material as the base underneath it or the polymeric sand that goes into the joints afterward.
5. The pavers
Set into the bedding sand in the chosen pattern, then vibration-compacted into the sand bed. This is the layer everyone sees, and it's also the layer that gets blamed for problems that almost always start three steps lower, in the granular base.
6. Polymeric jointing sand
Swept into the joints between pavers and activated with water, locking the surface together and preventing lateral shifting. It washes out gradually over years, especially where rock salt is used, which is why re-sanding on a regular cycle is part of ongoing maintenance, not a one-time step.
7. Edge restraint
Mechanically anchored restraint running the full perimeter of the installation, holding the field of pavers in place so it can't spread outward under load. An edge that corrodes or was never properly fastened lets the whole field loosen over time, which is one of the four classic ways interlocking driveways sink.
The honest summary: of those seven layers, only the pavers and the surface finish of the joint sand are visible once the project is done. Everything that actually determines whether the installation lasts 10 years or 40 is buried before the first paver ever goes down.
How deep should the base be in the GTA?
Base depth isn't a single number, it depends on the soil, the application, and the load the surface needs to carry. Here's how it actually breaks down across GTA conditions.
| Situation | Typical compacted base depth | Why |
|---|---|---|
| Standard driveway, well-draining soil | 8–10 inches | Baseline depth to carry vehicle load through GTA freeze-thaw cycling |
| Driveway on heavy clay soil | 10–12 inches | Clay holds water and moves seasonally; extra depth plus geotextile fabric compensates |
| Heavier loads, poor drainage, or large-format pavers | Up to 14 inches | Large-format pavers have less joint flexibility per square foot and are more sensitive to any settlement underneath |
| Walkways and patios (foot traffic only) | Shallower than a driveway | No vehicle load to support; still excavated, compacted in lifts, and graded correctly |
If a quote specifies a base depth below these ranges for a driveway application, ask why directly. There are occasionally legitimate site-specific reasons, but far more often, a shallow base is how a contractor gets a number low enough to win the job on price. Cut-rate quotes routinely spec 4 to 6 inches where 8 to 10 is the standard, and the difference doesn't show up until the second or third winter.
Compaction in lifts — why it matters more than raw depth
Depth alone doesn't tell the whole story. How that depth gets compacted matters just as much, arguably more.
If 10 inches of granular base material is dumped into an excavation and compacted in a single pass, a plate compactor only effectively densifies the top few inches. Everything underneath that stays loose, uncompacted material held in place only by what's resting on top of it. That loose material keeps settling, slowly, under its own weight and under the repeated expansion and contraction of freeze-thaw cycling, for years after the project is finished. It's one of the quieter reasons a driveway can look fine at handover and develop soft spots two winters later with no obvious cause.
Building the base correctly means compacting it in lifts, layers of roughly 3 to 4 inches, each one run with a plate compactor until it's properly densified before the next layer goes on top. It takes longer. It costs more in labour. It's also the only way to guarantee that every inch of material under the pavers is actually doing its job, not just sitting there waiting to settle.
"You can't tell a compacted-in-lifts base from a dump-and-compact base by looking at the finished driveway. You can tell within two winters, because one of them is still flat and the other one isn't."
— Reliable Hardscapes, on why compaction method matters as much as depthGranular A vs 19mm clear stone: dense-graded vs open-graded
The two most common base materials used across GTA interlocking projects work on opposite principles, and understanding the difference helps you ask a more useful question than just "how deep is the base."
Granular A (dense-graded)
Granular A is a crushed stone mix that includes fine particles, screenings or stone dust, alongside larger stone. Those fines fill the voids between the bigger pieces, which is exactly what lets this material compact into an extremely dense, stable, almost solid mass under a plate compactor. That density is what gives a driveway base its load-bearing strength, and it's the traditional default choice for residential interlocking across the GTA. The trade-off is that a tightly compacted, fines-filled base doesn't drain water through itself particularly well, so correct surface grading and a properly sloped base are what carry water away, not the base material's internal drainage.
19mm clear stone (open-graded)
Clear stone is the opposite approach: crushed stone with the fines washed out, leaving mostly uniform, larger pieces with open voids between them. Water moves through an open-graded base rather than sitting on top of it, which is why it's often paired with geotextile fabric and why it shows up in permeable interlocking systems designed specifically to manage stormwater at the base level rather than just on the surface. It compacts differently than Granular A, less about crushing fines into a solid mass and more about the stone pieces locking against each other.
Neither material is universally "better." The right choice depends on the drainage conditions and soil underneath a specific site, which is exactly the kind of judgment call that separates a contractor who assesses your property from one who quotes the same spec on every job regardless of what's actually there.
What base construction actually costs
Because base work is invisible once the project is finished, it's easy to underweight how much of your budget is actually going into it. Based on Reliable Hardscapes installations across the GTA in 2025–2026, here's roughly how a typical interlocking driveway project's cost breaks down at the base-construction level:
| Component | Typical % of total installed cost | What it covers |
|---|---|---|
| Excavation | 8–12% | Digging to the required base depth, soil removal, dump fees |
| Granular base material | 14–22% | Crushed stone (Granular A or clear stone), geotextile fabric, edge restraint anchors |
| Bedding sand & polymeric jointing sand | 3–5% | The 1-inch bedding sand setting layer, plus polymeric sand for the joints |
| Skilled labour (compaction-related portion) | 22–30% | Compaction in lifts, screeding, paver setting, edge installation |
Add it up and the material and labour living below the surface, excavation, granular base, bedding sand, and the compaction-heavy portion of labour, routinely lands at 35 to 45% of the total installed cost on a properly built driveway. The paver itself, meanwhile, is usually only 18 to 28%. That ratio is the whole reason "saving money" by downgrading the paver line barely moves the final number, while shortening the base does, which is exactly why it's the line item that gets cut first on a lowball quote.
Ontario-specific considerations
Freeze-thaw cycling demands real depth, not a shortcut
The GTA sees dozens of freeze-thaw cycles every winter. Water in an under-built or poorly compacted base expands roughly 9% in volume every time it freezes, and that expansion and contraction is what gradually heaves and settles a surface over years. A properly built, deep, well-compacted base is engineered specifically to resist this mechanical cycle. There's no climate-related shortcut available here, the depth and compaction standards exist because of Ontario winters, not despite them.
Clay soil changes the spec
A meaningful share of the GTA, particularly Mississauga, Brampton, and west Toronto, sits on heavy clay that holds water and shifts seasonally. A base built for sandy, well-draining soil elsewhere in the country will not perform the same way here. This is exactly why GTA-specific specs call for extra base depth and geotextile fabric on clay sites, and why a generic national pricing guide or a contractor unfamiliar with local soil conditions can get this wrong.
Permits and timing
Most municipalities don't require a building permit for base reconstruction on an existing driveway footprint, but projects that extend to the curb cut or change the driveway's footprint can trigger permit requirements. If you're planning a full rebuild, it's worth confirming this early, see our guide on when a permit is actually required for interlocking in the GTA.
Best time of year to rebuild a base
Base work depends on being able to properly compact material, which means avoiding frozen ground and avoiding oversaturated soil after heavy spring rain. Late spring through fall is the practical window for base reconstruction across most of the GTA; a base built on frozen or waterlogged ground won't compact correctly no matter how much time is spent on it.
Base construction mistakes that cost homeowners thousands
1. Quoting a shallow base to win the job on price
The single most common corner cut in GTA interlocking. A proposal that specifies 4 to 6 inches where the standard is 8 to 10 will look identical on install day and start showing settlement within a few winters. Ask for the base depth in writing before signing anything, and compare it against the ranges in this guide.
2. Compacting in one pass instead of lifts
Saves a few hours of labour on install day, costs years of surface life. There's no way to inspect this after the fact, which is exactly why it's worth asking directly how the base will be compacted, not just how deep it will be.
3. Skipping geotextile fabric on clay sites
A small material cost to omit, with a disproportionate impact on long-term base performance once clay starts migrating upward into the granular layer.
4. Using mason sand or generic sand instead of proper bedding sand
The wrong sand in the bedding layer compacts and drains differently than it should, leading to uneven settling under the pavers even when the granular base underneath was built correctly.
5. Skipping or under-anchoring edge restraint
Without a properly fastened perimeter, the entire field of pavers can spread outward under traffic and seasonal movement, loosening every joint across the surface over time, not just at the edge.
6. Ignoring drainage and grade during base construction
The base has to be graded correctly before a single paver goes down. Water that pools on or in the base instead of draining away is dramatically more damaging through winter freeze cycles than water that moves off the site as intended, and retrofitting drainage after installation costs far more than engineering it in from the start.
How to tell if an existing base was built properly
This is the frustrating part: you usually can't tell from the surface, which is exactly what makes base-depth cuts an easy thing for a cheap contractor to get away with for a few years. A few signs are still worth watching for.
- Settlement arriving early. Dips or low spots showing up within the first two or three winters point toward an under-built base rather than normal long-term wear.
- Movement in multiple areas, not one spot. A single isolated dip often has a traceable local cause (a downspout, a tree root). Broad, shallow settlement appearing in several places at once is the more typical signature of a base that was never deep enough or never compacted in lifts.
- Edges you can shift with your foot. This points to edge restraint that corroded or was never properly anchored, letting the field loosen at the perimeter first.
- New low spots appearing every spring. Suggests the base itself is failing on an ongoing basis rather than having settled once and stabilized.
If you're seeing this pattern, the fix is rarely a quick patch. Our guide on why interlocking driveways sink and how pros fix them permanently goes through the full diagnosis and repair process in detail, including how to tell a localized problem from a base-wide one.
FAQs about interlocking base construction
How deep does an interlocking base need to be in the GTA?
Most residential interlocking driveways in the GTA need 8 to 10 inches of compacted granular base. Properties on heavy clay soil, common across Mississauga, Brampton, and parts of Markham, often need 10 to 12 inches plus geotextile fabric. Driveways carrying heavier vehicle loads, poor drainage, or large-format pavers can need up to 14 inches. Patios and walkways, which only carry foot traffic, don't need to go nearly as deep, but the base still has to be excavated, compacted in lifts, and graded correctly.
What's the difference between Granular A and 19mm clear stone for a paver base?
Granular A is a dense-graded crushed stone that includes fine particles (screenings or stone dust) mixed with larger stone. Those fines fill the gaps between bigger pieces, which is what lets it compact into an extremely hard, stable mass, the traditional choice for driveway bases. 19mm clear stone is an open-graded material with the fines washed out, so water moves through it rather than sitting on top of it. Both are used across GTA interlocking projects; which one is right depends on the drainage conditions and soil underneath a specific site.
Why is compaction done in lifts instead of all at once?
If you dump 10 inches of granular base in one pass and compact it, the plate compactor only effectively densifies the top few inches, the material underneath stays loose. That loose material settles later, under its own weight and under freeze-thaw cycling, which is exactly how driveways end up with dips and low spots years after installation. Building the base in lifts (compacted layers, typically 3 to 4 inches each) means every inch of material gets properly densified before the next layer goes on top.
Do I need geotextile fabric under my interlocking base?
On clay-heavy GTA soil, yes. Geotextile fabric is laid between the native clay subgrade and the granular base to stop the two from mixing together over time. Without it, fine clay particles migrate up into the granular base under repeated freeze-thaw cycling and traffic load, which clogs the base's ability to drain and accelerates settlement. On sandier, well-draining soil it's less critical, but on the heavy clay found through much of Mississauga, Brampton, and parts of Markham, it's a standard part of a properly built base.
How much of my interlocking budget actually goes into the base?
On a typical GTA interlocking driveway project, excavation runs about 8 to 12% of the total installed cost and granular base material runs about 14 to 22%, meaning the base work alone accounts for roughly a quarter to a third of what you're paying. Add bedding sand and polymeric jointing sand at another 3 to 5% and the portion of your budget living below the surface, where you can't see it after the project is done, is often 35 to 45% of the total.
Can I use stone dust or mason sand instead of proper bedding sand?
No. The bedding layer under the pavers themselves is a thin, roughly 1-inch setting bed of high-performance bedding sand, a specific coarse, washed sand that provides a stable, even surface for the pavers to sit on. Mason sand and generic sand are finer and don't compact or drain the same way, they shift under traffic and allow uneven settling. This is a different material from the granular base underneath it and from the polymeric sand swept into the joints afterward, each layer has a specific job and a specific material that does that job properly.
How do I know if my existing driveway's base was built properly?
The honest answer is that you usually can't tell from the surface until something goes wrong, which is exactly the problem with cutting corners on base work. Warning signs include dips or low spots appearing within the first two or three winters, movement in multiple areas rather than one isolated spot, and edges you can shift with your foot because the restraint was never properly anchored. If a driveway installed within the last five to seven years is already showing broad, shallow settlement rather than a single traceable cause, an under-built base is the most likely explanation.
Does base depth change for a patio versus a driveway?
Yes, in principle, because the loads are completely different. A driveway has to support vehicle weight day after day through freeze-thaw cycling, which is why it needs a deep, engineered granular base. A patio only carries foot traffic and outdoor furniture, so the demands on the base are lighter. That said, the fundamentals don't change: excavate to the correct depth for the application, remove all organic material, compact in lifts, and grade properly so water moves away rather than pooling. Skipping those steps causes the same settlement problems on a patio that it does on a driveway, just on a different timeline.