GL InspectionsFoundation cracks: when should I worry?
Thin vertical or hairline cracks in poured concrete are usually shrinkage and are common, even in new homes. Worry more about horizontal cracks, walls that bow inward, stair-step cracks in block walls, cracks wider than about 6 mm (1/4 in), cracks that keep growing and cracks that let water in; those call for a structural engineer or foundation specialist.
Updated October 2026 · By Gerardo Lucero, Certified Professional Inspector (CPI)
Start with three questions
Almost every basement in the GTA has a crack somewhere. Concrete shrinks as it cures, and Ontario's freeze-thaw cycles and soil movement do the rest. The useful question is not "is there a crack?" but "what kind of crack is it?" I sort cracks with three questions:
- Which way does it run? Vertical, diagonal, stair-step or horizontal.
- How wide is it, and is one side offset from the other?
- Is there water or movement? Staining, efflorescence, damp patches, or signs the house above has shifted.
Level 1: usually fine, keep an eye on it
Thin vertical or hairline cracks in a poured concrete wall, with no offset and no water, are typically shrinkage cracks. Tarion's construction performance guidelines for new homes treat curing shrinkage cracks as normal, and set repair thresholds at 6 mm wide for poured concrete foundation walls, 2 mm for concrete block walls and 4 mm for basement floor slabs. You will see these in new subdivisions in Vaughan and Kleinburg as often as in older homes. A simple way to monitor: mark the ends of the crack with a pencil and date, and check again in a few months.
Level 2: seal it and fix the water
A vertical or small diagonal crack that shows water staining, a white chalky line or dampness is mainly a water problem. The fix is usually a crack injection or exterior repair by a waterproofing contractor, plus checking the grading and downspouts outside. See signs of water in the basement. For new homes, actual water coming through the foundation is covered under Tarion's two-year warranty; dampness and condensation are not. If you're within that window, the new home and Tarion inspection can help you document it.
Level 3: call a structural engineer
- Horizontal cracks, especially with the wall bowing or leaning inward
- Stair-step cracks in a block foundation, common in some 1950s to 1970s GTA homes
- Cracks wider than about 6 mm (1/4 in), or with one side pushed out past the other
- Cracks that grow, lengthen or come back after being repaired
- Cracks together with sloping floors, sticking doors or gaps above door frames
What I check above the crack
As a carpenter who has framed and renovated GTA homes since 2009, I don't stop at the concrete. Foundation movement shows up in the framing: floors that slope, door frames out of square, doors that rub, gaps where trim meets walls, and drywall cracks running from the corners of doors and windows. I report observed signs of possible foundation movement and active water penetration, as the InterNACHI Standards of Practice require. A home inspection is visual, so finished basements, stored items and drywall can hide walls, and I don't provide engineering opinions. When I see Level 3 signs, I recommend a structural engineer before you firm up.
A crack is one item in a full pre-purchase inspection. Book yours and I'll walk you through every crack I find.
Sources
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Questions people ask
are vertical cracks in basement walls normal
Thin vertical cracks in poured concrete are very common and usually come from shrinkage. Watch them for growth or water, and seal them if they leak.
horizontal crack in basement wall is it bad?
It's the type that worries me most, because it can mean soil pressure is pushing the wall in. Get a structural engineer to look before you buy.
does tarion cover foundation cracks
Tarion's guidelines treat normal shrinkage cracks as acceptable, but require repair of poured wall cracks wider than 6 mm and cover actual water leaks through the foundation for two years.
can a home inspector tell me if the foundation is ok?
I report visible cracks, water and signs of movement, but a home inspection doesn't include engineering. If I see serious signs, I recommend a structural engineer.
how do i know if a crack is getting bigger
Mark both ends of the crack with a pencil and the date, take a photo with a ruler beside it, and compare every few months.
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