What causes basement floors to heave, and can it be fixed?

Basement floor heaving is typically caused by hydrostatic pressure from groundwater or frost action beneath the concrete slab, and yes, it can be fixed, though the solution depends on the underlying cause and severity.

Floor heaving occurs when forces beneath your basement slab push upward with enough pressure to crack and lift the concrete. In Ottawa's climate, this is unfortunately common due to our clay soil conditions, freeze-thaw cycles, and seasonal water table fluctuations. The most frequent culprits include groundwater pressure during spring melt or heavy rainfall, frost penetration beneath inadequately insulated slabs, and expansive clay soil that swells when wet and contracts when dry.

Hydrostatic pressure is the leading cause in Ottawa basements. When groundwater rises due to poor drainage, blocked weeping tiles, or seasonal conditions, it creates upward pressure beneath your slab. This pressure can exceed the weight of the concrete, causing cracks and heaving. Frost heaving happens when moisture beneath the slab freezes and expands, particularly in older homes where the slab wasn't poured below the frost line (4 feet deep in Ottawa) or lacks proper vapor barriers.

Clay soil expansion is another significant factor in our region. Ottawa's Leda clay becomes plastic when wet and shrinks dramatically when dry. This constant expansion and contraction cycle can destabilize the base beneath your basement floor, leading to uneven settling and heaving over time.

Repair options range from minor crack filling to complete slab replacement, depending on severity. For minor heaving with small cracks, concrete crack injection and surface leveling may suffice, typically costing $1,500-$4,000. Moderate heaving often requires slab jacking (mudjacking), where polyurethane foam or concrete slurry is injected beneath the slab to level it, running $3,000-$8,000 for an average Ottawa basement.

Severe heaving usually necessitates slab removal and replacement. This involves excavating the damaged concrete, addressing drainage issues, installing proper vapor barriers and insulation, and pouring a new slab. Expect $15,000-$30,000 for a complete basement floor replacement, including addressing the underlying water issues.

Prevention is crucial and often more cost-effective than repair. Ensure your weeping tile system functions properly, maintain gutters and downspouts, and consider exterior waterproofing if you're experiencing recurring moisture issues. Interior drainage systems with sump pumps can also help manage hydrostatic pressure.

For any basement floor heaving in Ottawa, you'll want a professional assessment to determine the root cause. Don't ignore early signs like hairline cracks or slight unevenness – addressing water infiltration early can prevent major structural issues. Contact Ottawa Basements for a comprehensive evaluation of your basement floor issues and a customized repair plan that addresses both the symptoms and underlying causes.