What does a stair-step brick crack wider at the top mean?
In short: A stair-step crack in brick that is wider at the top than the bottom usually points to settlement, meaning part of the foundation below the crack has dropped and the wall has pulled apart above it. On Oklahoma clay, the most common reason is soil drying and shrinking under the slab edge, often near trees, but the crack is read together with a floor elevation survey before drawing conclusions.
What does this crack look like?
The crack follows the mortar joints in a staircase line, usually starting near a corner, window or door, and it is visibly wider at its upper end and closes to a hairline lower down. Stair-step cracking in brick veneer is among the damage that differential movement on expansive soils causes 3.
What does the taper tell you?
Brick industry guidance states that foundation settlement, especially on unstable or expansive soils, can cause diagonal or stepped cracks in brick and mortar directly above the foundation, and that settlement and deflection cracks have a tapering shape 1. Inspection guidance adds that rapid settlement produces tapering cracks, wide at one end and hairline at the other, often along mortar joints near corners and openings 2.
The wide end marks where the two parts of the wall have separated most. When the top is wider, the section of wall on one side has typically rotated down and away, which is the pattern associated with the foundation dropping under the lower end of the crack. Because neither source sets a fixed rule for reading taper direction, the pattern is confirmed by measuring the floor. A crack that is wider at the bottom is covered on its own page: stair-step crack wider at bottom.
What commonly causes this crack?
| Cause | How it drops part of the foundation |
|---|---|
| Perimeter drying settlement | Clay under the slab edge shrinks and the perimeter drops 3 |
| Tree-root desiccation | Trees and large shrubs withdraw soil water, causing downward movement 4 |
| Differential movement at additions | Settlement cracks form at joints with porches, bay windows and additions 2 |
| Slope creep | Clay on slopes can slowly drift downhill, causing settlement 2 |
| Karst subsidence | Sinkholes and caverns in soluble rock can cause land settlement 6 |
| Pier movement after repair | Inadequately anchored piers can move with the soil 3 |
Settlement from fill, soft alluvial soil and collapsible soil are other listed mechanisms, covered in the causes section.
Oklahoma context
Most of Oklahoma has expansive soils, and seasonal drying lets a slab perimeter drop 3. Karst, meaning rock that groundwater can dissolve, occurs in limestone in the northeast Ozark area and the Arbuckle Mountains and in gypsum and salt in many parts of western Oklahoma 6.
How is this crack documented?
- Width at both ends. Measure the crack at the top and bottom with a crack-width card, and photograph it with a scale in the frame.
- Age and activity. A clean crack edge suggests recent movement; a dirty or previously filled crack may be inactive 2. Width is read against building age: a half-inch crack in a new building may mean rapid settlement, while in a 50-year-old building it may reflect about 1/100 inch of movement per year 2.
- Monitoring. Crack monitors can record movement over time; cyclical movement may take six months or more to measure 2.
- Elevation survey. A relative floor elevation survey is the engineering step beyond a visual first impression 5. A low area near the bottom end of the crack supports a settlement reading. See elevation surveys.
Related
- Stair-Step Brick Crack Wider at Bottom
- Perimeter Drying Settlement (Edge Drop)
- Heave vs Settlement
- Distress Pattern Library
- Steel Push Piers
Common questions
What does a stair-step crack in brick mean?
A crack that steps up through the mortar joints is a common pattern of foundation movement in brick veneer. Brick industry guidance notes that foundation settlement, especially on unstable or expansive soils, can cause diagonal or stepped cracks in the brickwork directly above the foundation.
Why does it matter whether the crack is wider at the top?
Settlement and deflection cracks taper, wide at one end and hairline at the other. The wide end shows where the wall has pulled apart most, which helps identify which part of the foundation has moved, but an elevation survey is used to confirm it.
Is a wide crack in an old house as serious as in a new one?
Not necessarily. Inspection guidance relates crack width to building age: a half-inch crack in a new building may indicate rapid settlement, while in a 50-year-old building it may reflect slow movement of about 1/100 inch per year.
How do I know if the crack is still moving?
A clean, fresh crack edge suggests recent movement, while a dirty or previously filled crack may be inactive. A crack monitor read over six months or more can show seasonal movement.
Sources
- Volume Changes – Analysis and Effects of Movement (Technical Note 18) Brick Industry Association
- Inspecting Foundation Walls and Piers International Association of Certified Home Inspectors (InterNACHI)
- The Mystery of Expansive Soils STRUCTURE magazine
- Recommended Practice for the Design of Residential Foundations, Version 2 Texas Section, American Society of Civil Engineers
- Guidelines for the Evaluation and Repair of Residential Foundations, Version 3 Texas Section, American Society of Civil Engineers
- Mapping of Karst Terranes in Oklahoma to Identify Potential Environmental and Hydrologic Problems AAPG Search and Discovery (Oklahoma Geological Survey author)
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