How Deep Should Paver Base Be?
Interpret scoped CMHA base minimums and identify how traffic, subgrade, drainage, climate and pavement system control the required compacted depth.
Paver base depth is a pavement design choice, not a national fixed number. It depends on loading, subgrade strength, moisture, climate and the complete layer system. Specify the finished compacted aggregate thickness separately from bedding and paver thickness.
Read the common minimums with their conditions
CMHA PAV-TEC-002 gives minimum compacted bases of 4 inches for pedestrian areas and 6 inches for residential driveways over well-drained soils within its conventional interlocking pavement context. These are scoped minimums, not approval for every site.
The document’s context matters as much as the number. It does not make a waterlogged clay subgrade well-drained, classify truck traffic as a passenger-car driveway, or turn a permeable reservoir system into conventional sand-set construction. A deeper section may be necessary; some sites require drainage or subgrade treatment in addition to depth.
What controls the selected section
| Design factor | Information to establish | Why a default can fail |
|---|---|---|
| Application and traffic | Pedestrians, cars, deliveries, repeated turning or heavier vehicles | Loads and repetitions differ |
| Subgrade | Soil type, bearing condition, disturbed fill and uniformity | Weak pockets can settle even below a thick base |
| Water | Surface routing, groundwater, irrigation and an outlet | Persistent moisture changes support conditions |
| Climate | Local frost experience and thaw-season conditions | Seasonal loss of support and heave are site dependent |
| Pavement assembly | Dense-graded, open-graded, permeable, rigid or proprietary system | Each has different material and layer requirements |
Furniture on a patio is not the same load case as a vehicle. A walkway crossed by maintenance vehicles needs the crossing assessed rather than assuming the whole route is pedestrian-only.
Investigate soil before choosing inches
Remove organic surface material from the proposed bearing area and identify fill, soft zones and moisture conditions during site preparation. A dry surface crust does not establish the condition underneath. If excavation exposes unstable ground, follow the project’s assessment and treatment process before placing aggregate.
The clay-soil guide covers drainage and separation questions. Clay does not automatically mean one additional thickness, and a fabric layer does not independently approve a reduced base.
Include a water path in the detail
Show how surface water leaves the paving and how water within the assembly can reach a suitable outlet or designed infiltration area. Free-draining aggregate in a closed excavation can store water without solving disposal. Coordinate the detail with adjacent foundations, curbs and soil.
In cold regions, use local design information and the freeze-thaw guide. A patio layer need not copy a roadway section, but roadway research helps explain why soil, water supply and freezing interact. There is no defensible nationwide “add two inches for winter” rule.
Compacted thickness is an outcome to verify
The selected depth must remain after compaction. Placing one thick loose layer does not establish that outcome. Lift thickness, equipment, moisture and verification belong to the installation specification. A purchase allowance estimates material; it does not replace compaction quality control.
Check finished elevations and excavation depth once the assembly is selected. Increasing base thickness changes digging, disposal, material delivery and transitions at doors or existing paving.
Use the right application guide next
For vehicle projects, review driveway base depth and actual vehicle use. For pedestrian routes, review walkway base depth, especially transitions and crossings. Permeable systems need both structural and stormwater design, rather than adopting these conventional minimums without checking the system.
Once the project-specific compacted depth is established, enter it and the measured base footprint into the Paver Base Calculator. The base quantity guide explains the conversion from design volume to a supplier order.
Sources and scope
- CMHACMHA PAV-TEC-002 (formerly Tech Spec 2 / Tech Note 2): Construction of Interlocking Concrete Pavements
Conventional interlocking concrete pavement construction; scoped base minimums and nominal uncompacted bedding guidance.
- CMHACMHA PAV-TEC-010-22: Application Guide for Interlocking Concrete Pavements
Application, thickness, aspect ratio, and pavement system context; unit thickness alone does not approve a project.
- FHWAGeotechnical Aspects of Pavements — problematic soils and frost action
Soil, moisture and frost mechanisms in pavement engineering. Roadway treatment details are not universal residential patio prescriptions.
- CMHAConstruction of Permeable Interlocking Concrete Pavement Systems — PAV-TEC-018
Open-graded bedding, base and reservoir construction in permeable systems; not a substitute conventional sand-set detail.
Material specifications, construction guidance and product instructions have different scopes. Example inputs demonstrate calculations; they are not project defaults.