Foundation Cracks: What They Mean and When to Worry
What Foundation Cracks Looks Like
You might spot thin hairline cracks near the corners of windows or doors, wider cracks running diagonally like stair steps along mortar joints, or horizontal cracks running the length of your basement wall. Each pattern tells a different story about the forces acting on your foundation.
Some cracks are barely visible. Others are wide enough to fit a pencil into. You might notice them inside your basement, on exterior foundation walls, in your garage floor, or running through brick or stucco on the outside of your home. Sometimes the first sign isn’t the crack itself, but what happens around it: a door that starts sticking, a window that won’t close properly, or a gap opening between the wall and the ceiling.
Pay attention to whether the crack is static (not changing) or active (getting wider, longer, or showing fresh concrete dust along the edges). Active cracks are the ones that need prompt attention.
Why This Happens
Foundations crack for several reasons, and understanding the cause is the first step to knowing what to do about it.
Settlement cracks appear when the soil beneath your foundation shifts or compresses unevenly. In many parts of British Columbia, homes are built on clay-heavy soils that expand when wet and shrink when dry. This seasonal movement puts uneven stress on your foundation walls and footings. When one part of the foundation sinks more than another, the rigid concrete can’t flex with it, so it cracks.
Lateral pressure cracks happen when saturated soil pushes against your basement walls from the outside. These are typically horizontal and appear at roughly the mid-height of the wall, where the pressure is greatest. BC’s wet winters are a major contributor. When water-logged clay soil freezes and expands, it can exert enormous pressure against your foundation.
Shrinkage cracks form as concrete cures and loses moisture. These are usually hairline, vertical or slightly diagonal, and they appear within the first year or two after construction. They’re cosmetic, not structural, but they can provide pathways for water if left unsealed.
Structural overload cracks are less common but more serious. These occur when your foundation is carrying more weight than it was designed for, or when soil erosion has removed support from beneath the footings. They tend to be wider, often with visible displacement where one side of the crack is higher or further out than the other.
How Serious Is It? A Quick Guide
When in doubt, a free assessment takes the guesswork out of it.
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What You Can Do, and When to Call Us
Monitor at Home
Mark and measure your cracks. Use a pencil to draw short lines across each crack and write the date beside them. If the crack grows past your marks, it’s active. Take quarterly photos with a ruler or coin held next to the crack for scale.
Keep a simple log. Note the date, which crack, and the approximate width. This record is incredibly useful if you do need a professional assessment later, because it shows the rate of change.
Maintain your drainage. Clean gutters twice a year, make sure downspouts extend at least 6 feet from the foundation, and check that the soil around your home slopes away from the walls on all sides. Good drainage reduces the soil pressure that causes many cracks.
Control interior moisture. Run a dehumidifier in the basement if humidity stays above 60%. Excess moisture on the inside of the wall compounds problems caused by moisture on the outside.
Call a Professional
Any horizontal crack in a basement wall. Horizontal cracks always indicate lateral soil pressure. This is structural, regardless of the width.
Any crack wider than 6mm. Once cracks reach this size, the forces behind them are significant and unlikely to stop on their own.
Cracks that are growing between your measurements. If your pencil marks show the crack has moved since your last check, the underlying cause is active and progressing.
Cracks with water seepage. Water finding its way through a crack means hydrostatic pressure is building behind the wall. This combination of cracking and water entry often worsens quickly.
Cracks where one side is offset from the other. Displacement means sections of your foundation are moving in different directions. This is one of the clearest signs of serious structural movement.
Multiple new cracks appearing in a short period. If cracks appear or worsen after the spring thaw, this suggests a change in soil conditions, like a water table shift or drainage failure, that needs investigation.
Common Questions About Foundation Cracks
Small hairline cracks are common, especially in newer homes as concrete cures and settles. The concern isn’t whether you have cracks, it’s the type, direction, and whether they’re growing. Vertical hairline cracks under 2mm are usually cosmetic. Horizontal cracks, stair-step patterns, or any crack that’s widening over time should be assessed by a professional.
You can patch cosmetic cracks with hydraulic cement or epoxy injection kits from the hardware store. However, filling a crack doesn’t address the underlying cause. If the soil pressure or settlement that caused the crack is still active, the crack will return, often right next to your repair. For structural cracks, DIY filling can actually mask a worsening problem.
Direction matters most. Horizontal cracks are almost always structural, meaning soil is pushing your wall inward. Stair-step cracks suggest uneven settlement. Width matters too: anything over 5-6mm, or any crack that’s getting wider, needs attention. Also watch for displacement. If one side of the crack is higher or further out than the other, the foundation is actively moving.
Cracks caused by active forces like ongoing settlement, seasonal soil movement, or hydrostatic pressure will typically worsen. The underlying cause doesn’t resolve itself. A crack that’s 3mm today could be 10mm next year. That’s why monitoring and measuring is so important: it tells you whether you’re dealing with something that’s stabilized or something that’s progressing.
Cost depends entirely on the cause and severity. A cosmetic crack might just need monitoring. A structural crack caused by lateral soil pressure might require wall anchors or carbon fiber reinforcement. Settlement cracks might need underpinning with piers. The best first step is a free assessment where we identify the cause, explain your options, and give you a clear quote with no pressure.
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