Finding a crack in your home's foundation almost always triggers the same reaction: worry. The good news is that most foundation cracks are harmless. The less reassuring news is that some reveal a genuine structural problem. Telling them apart starts with three questions: what type? what direction? is it changing?

The main types of cracks

Shrinkage cracks. Concrete contracts as it cures in the months after the pour. These thin cracks — often vertical or web-like — are the most common and usually have no structural significance. They can, however, let water through and are worth sealing.

Vertical cracks. Often linked to shrinkage or slight settlement, they are frequently benign, but should be monitored — especially if they widen or start letting in moisture.

Stair-step (or diagonal) cracks. Typical of concrete-block walls, they follow the mortar joints in a "staircase" pattern. They often point to differential settlement of the soil: one part of the foundation is moving more than another.

Horizontal cracks. These are generally the most concerning. A horizontal crack indicates excessive lateral pressure on the foundation wall — from soil, water or frost. It may come with a bulging wall and calls for assessment without delay.

Why Quebec foundations are heavily stressed

In Quebec, two factors put foundations to the test. First, clay soils, very common in the St. Lawrence Lowlands: clay swells as it absorbs water and shrinks as it dries, which keeps the foundation working. Second, freeze-thaw cycles: water in the soil freezes, expands and pushes against the foundation walls, winter after winter. Add poor water management around the house — misdirected gutters, a clogged foundation drain — and the conditions for cracking are all in place.

When should you actually worry?

The most important criterion isn't the presence of a crack, but its movement. A crack that has been stable for years is generally less concerning, but context still matters. By contrast, a crack that changes is a warning sign. Watch in particular for:

  • a crack that lengthens, widens or changes shape over a few months;
  • the appearance of multiple new cracks;
  • any horizontal crack or any bulging of the wall;
  • water seeping through the crack;
  • doors or windows that suddenly stick, a possible sign of structural movement.

A moving crack often reflects an underlying issue — settlement, lateral pressure, poor drainage — that can lead to major damage if left uncorrected. Note, too, that the two risks are distinct: even without a structural issue, water infiltration through a crack should be corrected to prevent building damage.

Monitor first, then have it assessed

If the crack seems minor, document it: mark the ends in pencil with the date, measure the width and take photos. Within a few months you'll know whether it's moving.

As soon as a crack is changing, is horizontal, or leaves you with any doubt, the surest way to get a clear answer is to have it examined by a structural engineer. Our residential structural expertise determines the real cause of the crack (settlement, soil movement, overload), assesses its consequences and recommends the right repair. And if your crack is purely cosmetic, we'll tell you so.

Not sure how serious what you're seeing is? That's exactly the kind of question an engineer can answer. Contact our team in Quebec City and Lévis.

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