Finding a crack in your foundation is unsettling. Most of the time, though, it's a shrinkage crack with no structural consequence. Some cracks do point to a real problem, and you can usually tell them apart by three things: their shape, their direction, and whether they're moving.

The main types of cracks

Shrinkage cracks are by far the most common. Concrete loses water and contracts in the months after the pour, which leaves thin cracks, often vertical or in a spiderweb pattern. They don't usually affect the structure, but they can let water in, so they're worth sealing.

A vertical crack is often caused by shrinkage or slight settlement and is usually benign. Keep an eye on it anyway, especially if it widens or starts to show moisture.

Stair-step cracks show up mostly in concrete-block walls. They follow the mortar joints and often indicate differential settlement: one part of the foundation is sinking more than another.

Horizontal cracks are the ones we take most seriously. They point to excessive lateral pressure on the wall from soil, water or frost. If the wall is also bulging, have it assessed promptly.

What stresses foundations in Quebec

Two factors come up again and again. The first is clay, which is common throughout the St. Lawrence Lowlands. It swells when it absorbs water and shrinks as it dries, so the foundation moves from one season to the next. The second is frost. Water in the soil expands as it freezes and pushes against the walls every winter. Gutters that dump water at the base of the wall or a clogged foundation drain make both problems worse.

When to worry

What matters most is whether the crack is changing. A crack that has been stable for years is generally less concerning, although context still matters. A crack that changes should be taken seriously. Watch for:

  • a crack that lengthens, widens or changes shape over a few months;
  • new cracks appearing;
  • any horizontal crack or bulging wall;
  • water coming through the crack;
  • doors or windows that start to stick, which can mean the structure is moving.

A crack that keeps changing often reflects an underlying problem such as settlement, lateral pressure or poor drainage. Left uncorrected, that problem can cause major damage. Water infiltration is a separate issue: it should be fixed even when the crack itself is not structural.

Document it, then have it assessed

If the crack looks minor, start by documenting it. Mark both ends in pencil with the date, measure the width and take photos. After a few months you'll know whether it's moving.

If it is changing, if it's horizontal, or if you're unsure, have a structural engineer look at it. During a residential structural assessment, we determine the cause of the crack (settlement, soil movement, overload), assess its consequences and recommend the appropriate repair. If it's purely cosmetic, we'll tell you that too.

To have a crack assessed, contact our team in Lévis.

This article is provided for general information and does not replace an on-site assessment by an engineer.