Why depth matters in Canada
Across much of Canada the ground freezes to a meaningful depth each winter. When wet soil freezes, the water in it expands and pushes upward. This is frost heave, and it is the main reason garden paths tilt, crack and separate. A granular base interrupts the process by draining water away before it can freeze under the stone and by spreading load so movement is gradual and even.
Local frost depth varies widely by region, so confirm the figure for your area with a municipal building department before settling on an excavation depth. Treat the depths below as relative guidance, not a fixed number.
Sequence of work
- Mark and excavateLay out the path and dig down through topsoil into firm subsoil. Topsoil holds water and organic matter and should not remain under a path.
- Shape a slight slopeGrade the bottom of the excavation to fall gently away from buildings so water drains rather than pools.
- Add granular sub-baseFill with a well-graded crushed aggregate that compacts tightly while still draining. Build it up in layers rather than all at once.
- Compact each layerCompact in lifts of roughly 75–100 mm. Compaction is what gives the base its strength; a thick uncompacted layer will settle later.
- Add a setting bedTop the compacted sub-base with a thinner layer of bedding material appropriate to the surface you are laying.
Filling the excavation in one deep pour and compacting only the surface. The lower material stays loose, holds water, and settles unevenly after the first freeze. Build and compact in thin layers instead.
Drainage and edges
Water that cannot escape is the real enemy. A free-draining sub-base, a slight cross-fall and edge restraints that do not trap water all work together. Edge restraints also stop the surface stones and bedding from migrating sideways over time, which keeps joints tight.
Geotextile separation
On soft or silty ground, a separation geotextile placed between the subsoil and the granular base helps stop the two from mixing. Mixing fills the voids in the aggregate, which reduces drainage and reintroduces the frost problem the base was meant to solve.