My garage floor is heaving and cracking from frost — what can I do to fix it in Ottawa?

Frost heave damage in garage floors is one of the most common and frustrating problems Ottawa homeowners face, and it happens because of a combination of our deep frost penetration, clay-heavy soils, and the fact that many garage slabs were not built with adequate frost protection or drainage. The good news is that it can be fixed — but the right repair depends on how severe the damage is and what caused it.

Minor heaving — where the slab has shifted up to half an inch and developed a few cracks but is still mostly functional — can often be addressed with concrete levelling and crack repair. Polyurethane foam injection (often called mudjacking or slab jacking) involves drilling small holes through the slab and injecting expanding foam beneath it to lift settled sections back to level. This costs $1,500 to $3,500 for a two-car garage and takes a few hours. Cracks are then repaired with a flexible polyurea or epoxy filler that can handle ongoing movement. This is a practical solution when the heaving is isolated to one area — commonly near the garage door threshold where cold air penetration is greatest — and the rest of the slab is sound.

Moderate heaving — where multiple sections have shifted, cracks are wider than a quarter inch, and the slab is noticeably uneven across much of its area — usually requires slab removal and replacement. Tearing out and replacing a two-car garage slab in Ottawa typically costs $8,000 to $15,000, which includes demolition, disposal, base preparation, and a new pour. If you are going through this expense, it is the perfect time to address the root cause so the problem does not repeat.

The root cause in Ottawa is almost always one of three things, often in combination. Inadequate base preparation — if the original slab was poured over undisturbed clay soil without a proper granular base, water collects beneath the slab, freezes, and heaves it upward. Missing or failed drainage — without proper grading away from the garage and functional weeping tile around the perimeter, water accumulates against and under the foundation. No insulation at the slab perimeter — cold air penetrating from the garage door side can drive the frost line beneath the slab edge, especially in unheated garages.

When replacing a heaved slab, a competent Ottawa contractor will address these issues. The proper approach includes excavating the subgrade and replacing it with 6 to 8 inches of compacted granular base (typically Granular A or clear stone) that drains freely and does not hold moisture. A 6-mil polyethylene vapour barrier goes over the granular base to block moisture migration. If the garage is unheated, rigid foam insulation (R-10 minimum) around the slab perimeter prevents frost from penetrating beneath the edges. The new slab itself should be a minimum 4 inches thick with 32 MPa concrete reinforced with welded wire mesh or rebar, and should include properly placed control joints to manage future cracking.

Drainage around the garage is equally important. The grade outside the garage should slope away from the foundation at a minimum of 2% (about 1 inch per 4 feet) for at least 2 metres. If your lot does not allow this — common in Ottawa neighbourhoods with flat lots or rear-yard drainage issues — a French drain or catch basin system may be necessary.

Do not ignore progressive heaving. Each freeze-thaw cycle worsens the damage, and a heaved slab eventually affects the garage door operation, wall framing, and even the roof structure if the foundation shifts enough. Connect with experienced concrete and garage foundation contractors through Ottawa Garages to get an honest assessment of your situation.

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Looking for experienced contractors? The Ottawa Construction Network connects Ottawa homeowners with qualified professionals:

• 613Bins
• RenoMotion Inc.
• Grunt Work 4 Grunts
• Steven Labelle - Your Complete Home Renovator
• JMY Renovations