Commercial interlocking base fails from the ground up, not from the surface down. A parking lot or plaza carries repeated vehicle loading, turning pressure, and pedestrian traffic that a residential driveway never sees, and the base underneath has to be built for that reality, not scaled up from a residential spec.
In practice, that means a heavier Granular B sub-base under a Granular A base course, deeper than many residential applications and sized to the traffic type, with compaction requirements set by the project specification, and edge restraints designed for the expected vehicle loading. Here is what changes at commercial scale, and why it matters.
Key Takeaways
- Commercial interlocking generally uses a Granular B sub-base under a Granular A base course, both sized up from residential specifications for repeated vehicle load
- Base depth is set by traffic type, light-duty areas like visitor parking need less than heavy-duty truck routes and loading areas
- GTA clay-heavy soils can require a geotextile separation layer, with CBR or other geotechnical testing used on larger or more engineered developments
- Commercial projects may specify Modified Proctor testing or other project-specific compaction requirements, depending on the design and loading
- Edge restraints for vehicle traffic use aluminum, steel, or concrete systems, not the plastic or composite restraints common on residential jobs
Why Commercial Base Requirements Are Stricter Than Residential
A residential driveway sees a car or two, parked or moving slowly, a few times a day. A commercial lot sees delivery trucks, waste collection vehicles, and a steady flow of cars turning, braking, and idling in the same spots, day after day, year after year.
That repeated loading is what breaks down an under-built base. Turning pressure in particular concentrates stress at a single point rather than spreading it evenly, which is why entrances, turning radii, and loading areas fail first when a commercial base is undersized. The base has to be engineered for that pattern of use from the start, not built to a residential spec and hoped to hold.
Granular A and Granular B for Commercial Loads
Ontario’s standard specifications define Granular A as a dense-graded base course material and Granular B as the well-graded sub-base layer beneath it, the same two materials used on residential jobs. What goes into a proper interlocking base in Ontario covers what these materials are and how they work at residential scale.
Granular A
Dense-graded base course, placed closest to the surface, providing a stable, well-compacted layer for the bedding sand and pavers above it.
Granular B
Well-graded sub-base, placed beneath the Granular A layer, distributing load down into the subgrade.
The engineering principle does not change between residential and commercial work, the loading does. At commercial scale, both layers generally get built thicker and to a larger overall section to carry repeated vehicle load rather than occasional passenger traffic.
Base Depth by Traffic Type: Light-Duty vs Heavy-Duty
Base depth is not a single commercial number, it is set by what the surface actually carries. How deep interlocking should be excavated in Ontario covers residential depth in detail. Commercial work starts from that baseline and adds depth as loading increases.
Residential
Sized for occasional passenger vehicle traffic and parking
Light-Duty Commercial
Visitor parking, walkways, plaza entrances, deeper than residential
Heavy-Duty Commercial
Truck routes, loading docks, waste collection access, deepest section on the property
On the commercial jobs we build, we generally install and compact 12 inches or more of base material for standard commercial areas, more for heavy-duty sections, which is why a single parking lot can have two or three different base specs across its footprint depending on what each section carries.
Geotextile Fabric and GTA Clay Soil
Much of the GTA sits on clay-heavy soil that drains poorly and moves with moisture. Left unaddressed, that movement lets base aggregate migrate down into the subgrade over time, a problem sometimes called pumping, which softens the base from below even when everything above it was built correctly.
Where Testing Comes In
A geotextile separation fabric laid between the subgrade and the granular base keeps the two layers from mixing while still allowing water to pass through. On larger commercial developments, a CBR (California Bearing Ratio) soil test is sometimes required to measure how much load the native subgrade can actually support, since weaker subgrade soil generally calls for a thicker base section above it.
Compaction Standards for Commercial Sites (Modified Proctor)
How paver compaction works covers the mechanics of compaction itself, plate compactors, passes, moisture content. What changes at commercial scale is the level of compaction required by the project specification.
| Test Standard | Typically Used For | Compactive Effort |
|---|---|---|
| Standard Proctor | Residential interlocking and lighter-duty work | Lower |
| Modified Proctor | Commercial and other heavily loaded pavement work | Significantly higher |
Modified Proctor applies more compactive energy in testing and better reflects the heavier equipment and repeated loading a commercial base actually experiences. Specified density targets depend on the project’s engineering specification and the required loading, rather than a blanket number applied to every site.
Edge Restraints for Vehicle Traffic: Types and Placement
What edge restraints do and why they matter covers the full explanation of how edge restraints hold a paver field together. At commercial scale, the restraint itself changes.
Commercial vehicle areas generally call for edge restraint systems selected for the expected loading. Depending on the design, that may include aluminum, steel, or concrete curb systems rather than the lighter plastic or composite restraints commonly used in residential applications. The selected system needs to be strong enough to hold its position under repeated turning and braking forces.
Placement matters as much as material. These points typically see the highest stress and get reinforced restraint placement beyond what a straight run of edge needs.
Entrances
Turning Radii
What Happens When Any of These Specs Is Skipped
Skip any one of these specs and the surface tells on it eventually, usually sooner than anyone expects.
An undersized base ruts under repeated wheel loads, forming depressions along the paths vehicles actually drive
A subgrade without separation fabric lets aggregate pump down into clay over time, softening the base from underneath
Compaction that falls short of the target settles unevenly once traffic starts loading it
Edge restraints not rated for vehicle traffic let the whole field spread outward, often the first visible sign something below is wrong
None of these failures happen because interlocking as a material is weak. They happen because the base underneath was not built for what the surface ended up carrying.
Building It Right From the Ground Up
Getting these specs right is a decision made before a single paver is placed, not something correctable afterward without tearing the surface back up. If you are planning a commercial project and want the base built to the actual load it will carry, we are happy to walk through what your site needs.
Building a Commercial Surface That Has to Last?
Get a base spec built for your actual traffic, not a generic template.
Frequently Asked Questions
What is the difference between Granular A and Granular B?
Granular A is the dense-graded base course placed closest to the surface. Granular B is the well-graded sub-base beneath it. Both are used at residential and commercial scale, sized differently for the load.
How deep does a commercial interlocking base need to be?
It depends on traffic type. On our commercial projects we generally install and compact at least 12 inches of base material, more for heavy-duty sections, though the right depth for a specific site depends on soil conditions and load.
Why does clay soil in the GTA affect commercial base design?
Clay-heavy soil drains poorly and can let base aggregate migrate down into the subgrade over time. A geotextile separation fabric between the subgrade and the base prevents this while still allowing water through.
What is Modified Proctor compaction and why does it matter here?
It is a laboratory density test that applies more compactive energy than the Standard Proctor test typically used residentially, and it better reflects commercial loading. Some commercial specifications reference Modified Proctor targets, depending on the project design and required loading.
Do commercial parking lots need different edge restraints than residential driveways?
Generally, yes. Commercial vehicle areas call for edge restraint systems selected for the expected loading, which may mean aluminum, steel, or concrete curb systems rather than the lighter plastic or composite restraints common on residential driveways.
Disclaimer: This article reflects our research, project experience, and our own views. Base specifications depend on soil conditions, traffic loading, and project-specific engineering requirements, so treat this as general guidance, not a substitute for a site-specific geotechnical assessment. If you have questions about your specific project, reach out and we will walk through it with you.