Why interlock driveways in Barrhaven, Orléans and Stittsville sink and heave: base depth, drainage and polymeric sand
Updated
Most sunken or heaved interlock in Ottawa's newer suburbs traces back to the base and to water. Here is what the industry spec calls for, how frost moves a driveway, and what a re-level can and cannot fix.
What sits under a good interlock driveway
The pavers are only the top few centimetres. The part that decides whether a driveway stays flat is underneath.
The Concrete Masonry & Hardscapes Association (CMHA), the North American industry body for interlocking pavers, recommends 60 mm (2 3/8 in.) pavers for residential driveways. Under them goes a screeded layer of bedding sand, about 25 mm (1 in.) thick and left uncompacted until the pavers are vibrated in.
Under the sand is compacted crushed stone. CMHA's minimum for a residential driveway on well-drained soil is 150 mm (6 in.). Its application guide recommends 150 to 200 mm, and more where soils stay wet, are weak, or freeze hard. Both the stone and the soil below it should be compacted to at least 98% of standard Proctor density. In practice that means placing the stone in thin lifts and running a plate compactor over each one.
Around the outside there has to be an edge restraint. Without it the outer rows creep outward, the joints open and the sand washes out.
How frost moves a driveway
An Ottawa winter drives frost far deeper than any driveway base. A 150 to 300 mm base cannot keep frost out. Its real job is to drain, so there is little water left in and under it to freeze.
Large parts of the Ottawa area sit on Champlain Sea clay, often called Leda clay. Fine soils like this hold water. When a wet clay subgrade freezes under a thin base, it swells and lifts the pavers. In spring the ground thaws from the top down. The meltwater has nowhere to go, the soil turns soft, and the weight of a car pushes the pavers down. That is the heave-in-winter, sink-in-spring pattern many homeowners see.
CMHA notes that a geotextile fabric can be used over clay and moist silty soils and where there is freeze and thaw. It keeps the clay from mixing up into the stone, which is what slowly turns a good base into a soft one.
Slope matters just as much. CMHA calls for a minimum slope of 1.5%, and 2% is a common target. At 2% the surface drops 2 cm over every metre. A driveway laid flat, or pitched toward the garage, holds water right where it does the most harm.
Why 2000s subdivisions show it first
Much of Barrhaven, Orléans and Stittsville was built out in the 2000s. A driveway laid in 2005 is 21 years old in 2026, which is about when base problems stop being small.
When a driveway from that era is lifted, the usual things to look for are simple. How deep is the stone, measured, not assumed? Is there fabric over the clay? Was the strip beside the garage and house built over foundation backfill? Backfill against a new foundation keeps settling for years, and a driveway laid over it early will dip along the house.
Downspouts are the other common cause. A downspout that empties onto the interlock, or into a bed right beside it, feeds water straight into the base every time it rains.
Where polymeric sand fits
Polymeric sand is joint sand with a binder that hardens once it is wetted. It holds the joints, slows weeds and ants, and keeps the sand from washing out. It does not fix a failed base, and it will crack if the pavers under it keep moving.
It also has to be installed to the maker's conditions. Techniseal's data sheet for its RG+ product calls for a joint depth of at least 4 cm (1.5 in.) and joints between 1.5 mm and 2.5 cm wide. The pavers must be dry. The temperature should stay above 0°C for the 48-hour drying period, the maker recommends planning for 24 hours without rain, and vehicles should stay off for 24 to 48 hours.
In Ottawa that means late spring to early fall, on a dry forecast. A thin skim of new sand over old, shallow joints is the most common reason polymeric sand washes out after one season.
What re-levelling fixes and what it does not
A proper re-level, often called a lift and relay, goes like this. The pavers in the problem area are lifted and stacked. The old bedding sand comes out. The base is topped up with stone and compacted again. Fresh sand is screeded, the pavers go back down, the edge restraint is reset and the joints are refilled.
That fixes most local problems: a dip over settled backfill, a sunken corner, a soft spot at the end of a downspout, an outer row that has spread, or joints that have washed out.
It does not fix a base that is too thin across the whole driveway, clay that has already pumped up into the stone, or a slope that sends water toward the house. Those need the base dug out and rebuilt, which is closer to a replacement.
Signs worth a closer look: ruts in the wheel paths, a dip along the garage, puddles that stay a day after rain, pavers spreading at the edges, and sand on the surface after every storm. Indicative 2026 ranges from the price guide on this site: $200 to $600 for a small spot repair and $1,500 to $5,000 to lift and relay a larger section or a whole driveway, before HST. Before any work starts, ask the contractor how deep they will dig, whether they will add fabric, and where the water will go.