Guide
Stair-Step and Diagonal Foundation Cracks
What does a stair-step foundation crack mean, and should I worry?
A stair-step crack runs diagonally along the mortar joints of a block, brick or rubble wall, stepping down joint to joint like stairs. In Calgary it usually points at differential movement: one part of the wall moving slightly relative to another, either because the wall is settling or because the soil beside it is pushing. Because it sits on mortar rather than through the block itself, the crack faces usually stay flush, which is why these are often stable and modest. What turns one into a concern is whether the movement is ongoing, which measurement over time, not a single look, reveals.
We are a referral service, not a contractor. Your request goes to an independent Calgary foundation company.
Published by Calgary Foundation Pros. Last updated August 16, 2026. This is general guidance for Calgary homeowners, not an engineering assessment of any specific property, and it is not a substitute for a professional engineer where one is warranted.
Foundation cracks sort into a handful of readable families, and stair-step cracks are the one where direction is a little less informative than the pattern. A vertical crack is usually shrinkage; a horizontal crack is usually bending. A stair-step crack is usually movement between rigid units.
The useful questions are whether any part of the wall has shifted down or toward you, and whether that shift is happening now.
Why a crack becomes stair-step shaped
Block, brick and stone walls are built from rigid units held together by weaker mortar. When one part of the wall moves relative to another, the weakest path is the mortar, so the crack follows the joints in steps rather than cutting cleanly through the units.
This is why stair-step cracks appear far more in older Calgary masonry foundations than in modern poured concrete walls, which crack in straighter lines.
The two movements that produce the pattern
Stair-step cracks come from a wall's parts moving, and the direction of the steps hints at which.
- Settlement: a section of wall settling down pulls a diagonal line through the joints, often at a corner or near a large opening
- Lateral pressure: soil pushing inward tilts the wall and the stair pattern runs accordingly
- Both at once on different sections of the same wall is possible, which is why a measured history beats a first impression
How to tell a settling stair-step from a stable one
The decisive observation is change, and it is cheap to get.
- Mark the ends of the crack in pencil with today's date on both sides of the gap
- Measure the widest point and the opening at the mortar steps, and record the numbers
- Photograph it with a ruler or coin for scale, dated
- Look for settlement companions: sticking doors, sloping floors, other diagonal cracks in that corner of the house
- Re-check in three to six months, and again after the spring melt
When it warrants a professional look
A flush, stable stair-step crack with no settlement company is commonly watched rather than repaired. It moves into the assess-promptly category when it has company.
- The two faces are no longer flush, or one block has dropped below the line of its neighbours
- The crack is getting wider against a dated measurement
- A door or window in that part of the house is binding, or a floor is sloping
- More stair-step cracks appear within a short period
- Water is following the crack during melt
Questions people actually ask
Are stair-step cracks a bad sign in a foundation?
Not by themselves. A stair-step crack marks the joints of a masonry wall and commonly appears when a wall has settled a little and then stabilised. What would make it a bad sign is ongoing movement, which is why the next step is dated measurement and a re-check rather than an immediate repair.
What causes stair-step foundation cracks?
Movement between the rigid units of a masonry wall, most often differential settlement where one part of the wall settles more than another, or soil pressure from outside. The crack follows the mortar joints because they are weaker than the blocks themselves.
When should I worry about a diagonal foundation crack?
When it is accompanied by other settlement signs: blocks out of line, sticking doors, sloping floors, or the crack measurably widening over months. A single flush crack that stays the same width is generally fine to monitor.
Can a stair-step crack be repaired?
Yes, and the right method depends on whether the movement has stopped. For a stable crack the repair seals and restores mortar or the wall face. For one that is still moving, the movement has to be addressed first, which is an engineer-led question rather than a sealing task.
Want someone to look at your specific case?
General guidance only goes so far. Send a description and a postal code and it goes to an independent Calgary foundation contractor.
We are a referral service, not a contractor. Your request goes to an independent Calgary foundation company.