Lifted Sidewalks and Cracked Driveways: Living With Surface Roots

A raised slab of sidewalk with a root running under it is one of the most common tree conflicts in the city, and one of the most poorly handled. The reflex is to cut the root, repour the concrete, and move on, which frequently leaves a tree that fails in a storm three years later.

Understanding why roots end up under the concrete in the first place points toward repairs that fix the trip hazard without destabilizing a mature tree.

Why Roots Grow Where They Do

Roots grow where there is air, water, and room. In Calgary's compacted clay, the loosest, best-aerated soil on a property is often the bedding sand and fill under a walk or driveway, and moisture collects under slabs because they shed rain to the edges and slow evaporation.

So roots are not attacking the concrete; they are taking the easiest path available. As a root enlarges in diameter year after year, it lifts whatever sits on top of it, and concrete has no give.

Cutting Roots Has a Cost

Severing a large structural root close to the trunk removes both anchorage and a share of the tree's water and nutrient uptake. Do that on two or three big roots on the same side and you have meaningfully compromised the tree's stability, even though it looks fine the following summer.

A general guideline is to avoid cutting roots larger than about five centimetres in diameter, and to stay well away from the trunk, ideally no closer than several times the trunk diameter. Damage from root cutting shows up as decline or a windthrow failure years later, which is why it is so rarely connected back.

Repairs That Work With the Tree

There are better options than cut and repour. Grinding or shaving a raised slab removes the trip hazard where the lift is modest. Replacing a rigid slab with flexible paving, gravel, or rubberized surfacing lets the surface move as the root grows.

Rerouting the path around the root zone solves it permanently where layout allows. Where a slab must be replaced, ramping the new concrete over the root, or bridging with a thicker reinforced section, avoids cutting the root at all.

Root Barriers and Their Limits

Root barriers installed at planting time genuinely help direct roots downward and away from pavement. Installed after the fact, next to an established tree, they require trenching that cuts the very roots you are trying to redirect.

That does not make them useless later, but it does mean they need careful placement, usually at a distance from the trunk, and they are a partial measure rather than a cure.

Preventing It in New Plantings

The long-term fix is soil volume. A tree planted in a narrow strip between a sidewalk and a curb has nowhere else to go, and surface rooting is inevitable. Larger planting beds, structural soil, or simply siting big trees away from hardscape avoids the conflict entirely.

Species choice helps too. Some trees are notorious surface rooters, and planting one beside a driveway is a decision you live with for decades.

Who Is Responsible in Calgary

Public sidewalks, boulevard trees, and City-owned trees come with their own rules about what a homeowner may and may not do, and cutting roots on a City tree is not a decision to make on your own. Check before work starts.

On private property, the choice is yours, but it is worth an assessment first. Aardvark Tree Care can tell you which roots can be safely cut, which cannot, and which repair option protects both your walkway and your tree.

Cut two big structural roots on the same side and the tree may stand for years, then not.