A stair step crack in a foundation follows the mortar joints of a block wall, and it means part of the wall or the footing under it has moved. Many are minor, but you can't tell which from the basement floor, so have a structural engineer look before anyone patches it. A diagonal crack in a poured concrete wall is a different case: a thin one running from a window corner is usually shrinkage.
What does a stair step crack in a foundation mean?
It means part of a block wall has moved and the mortar joints gave way. ASHI’s Tom Feiza defines step cracks as cracks that follow the mortar joints in a block wall (opens in a new tab), and says many come from minor footing movement, shrinkage or wall movement. He adds that wide step cracks, or step cracks combined with other cracks and movement, indicate a problem.
Mortar is weaker than the block, so when the wall is pulled or pushed, it splits along the joints. The crack steps across one block, down one course, and across again. In a poured concrete wall there are no joints to follow, so the same kind of movement shows up as a diagonal or vertical crack instead.
So the first question isn’t how wide the crack is. It’s what the wall is made of, and where the crack starts.
Is a stair step crack in a block wall serious?
Sometimes, and that’s why it goes to an engineer. Some step cracks are old and stable; others are the first sign of a settling corner or a wall that’s being pushed in. The difference is in the details around the crack, and an engineer can read those in one visit.
Treat it as more urgent if you see any of these:
- The two sides no longer line up. Pillar To Post says a typical settlement crack opens like puzzle pieces, and if the faces have moved any other way, it can be a significant structural concern (opens in a new tab).
- There’s a horizontal crack or a bow in the same wall. Feiza says a horizontal crack combined with step or vertical cracks indicates a problem (opens in a new tab). See the horizontal crack guide.
- Both walls at a corner are cracked. Feiza notes that when a corner settles, step or vertical cracks develop on both adjacent walls.
- The crack is much wider at one end. InterNACHI describes settlement cracks that taper from large at one end to a hairline at the other (opens in a new tab).
- The cracking carries on upstairs. InterNACHI lists cracked walls, warped door and window openings, sloped floors and sticking doors as signs of differential settlement.
- A repaired crack has cracked again. Pillar To Post says a re-cracked repair (more than a hairline) could indicate ongoing movement.
- The crack edges look clean and fresh. InterNACHI notes that a clean crack indicates recent movement, while a dirty or previously filled one may be inactive.
The less worrying ones are step cracks at a window or under the end of a beam. Feiza says step cracks often occur at the weak point of a wall (opens in a new tab), around window openings, and are common at beam-end walls as the footing settles slightly. Those are the ones an engineer is most likely to call minor, but let the engineer make that call.
Width isn’t a reliable test on its own. Pillar To Post treats a settlement crack, or a series of them, with a total opening under 1/4 inch as probably not ongoing settlement, but adds that there are no hard and fast rules. A thin step crack next to a bowing wall is still serious.
What causes stair step cracks in a block foundation?
Mostly settlement, soil pressure or shrinkage. The pattern of the cracks points to which one, which is what the engineer will look at.
| What you see | Likely cause | How serious |
|---|---|---|
| Step cracks near a corner, often on both walls, wider at one end | Footing settlement at that corner. Pillar To Post says that for block or brick, settlement often shows as cracks that follow the mortar joints in a step pattern (opens in a new tab) | Engineer. Most settlement happens early and stops, but only a check tells you |
| Step cracks running from the corners toward a horizontal crack in the middle of the wall | Soil pressure pushing the wall in. Feiza says the corners stay stable while the wall breaks away (opens in a new tab) | Serious. See bowing basement walls |
| Old step cracks in the middle third of the wall, footing intact, no change for years | Drying shrinkage of the block. InterNACHI says these usually form in the first year and are rarely serious | Usually minor, but have it confirmed |
| Step cracks from a window corner or under a beam end | A weak point in the wall, or slight settling under the beam load | Often minor, per Feiza |
Water is behind a lot of it. Saturated or expansive soil pushes on the wall, and soil that washes out or dries and shrinks under the footing lets it drop. InterNACHI’s list of settlement causes includes soil shrinkage from nearby trees, blocked drainage and erosion from faulty drains (opens in a new tab).
What does a diagonal foundation crack mean in a poured wall?
It depends on where it starts. A thin diagonal crack running from the corner of a window or door is usually shrinkage. A diagonal crack near a corner of the house, wider at one end, is more likely settlement.
The NRMCA calls the window and door kind re-entrant corner cracking (opens in a new tab) and says these cracks result from shrinkage. Concrete shrinks as it dries, and the stress gathers at the sharp corner of the opening.
Treat a diagonal crack in a poured wall like a vertical crack if all of these are true:
- It starts at a window, door or other opening.
- It’s under 1/8 inch wide.
- The two sides are flush, with no step.
- It isn’t getting wider. The crack monitoring guide shows how to check.
Call an engineer instead if it’s 1/4 inch or wider, offset, growing, or there are other cracks with it. Feiza notes that when a poured wall bows, it shows a combination of vertical and 45-degree cracks (opens in a new tab) rather than step cracks. The NRMCA says to seek professional advice for active cracks that are widening with time (opens in a new tab).
| Stair step crack (block wall) | Diagonal crack (poured wall) | |
|---|---|---|
| Path | Follows the mortar joints in steps | Runs through the concrete at an angle |
| Most common cause | Settlement, soil pressure or block shrinkage | Shrinkage at a window or door corner |
| When it's serious | Offset, tapered, at a corner, with a horizontal crack or bow, or growing | Away from openings, 1/4 inch or wider, offset or growing |
| DIY crack injection kit | Not suitable. Kits are made for solid poured concrete | Fine for a thin, stable crack, like a vertical crack |
| First step | Structural engineer | Measure it, then monitor it |
Can you fix a stair step crack in a block wall yourself?
Not the cause, and filling the crack doesn’t fix anything. DIY injection kits are made for solid poured concrete, not hollow block. A wall that’s settling or being pushed needs an engineer’s plan first.
Don’t tuckpoint, caulk or paint over the crack before the engineer sees it. A fresh patch hides how wide the crack is and whether it’s growing. InterNACHI also warns that re-mortaring cracks that open and close with the seasons (opens in a new tab) holds them open and causes more cracking.
What you can do now:
- Mark and date the crack. Pencil a line across each end and the widest point, write the date, and photograph it. The monitoring guide shows how to keep a log for the engineer.
- Move water away from the wall. Clear gutters, extend downspouts and fix low spots. The NRMCA recommends a slope of 1/2 to 1 inch per foot for at least 8 to 10 feet (opens in a new tab) from the foundation.
- Check the rest of the house. Note any sticking doors, new drywall cracks or sloping floors near that wall.
How is a stair step crack repaired?
The engineer fixes the movement first, then the crack. What that takes depends on the cause, so there’s no standard repair for a step crack.
- Settlement. Feiza says significant settlement often requires an engineered-design solution (opens in a new tab), which may include soil testing and piers that carry the footing down to stable soil. InterNACHI lists pilasters and underpinning as other ways to strengthen the foundation.
- Soil pressure. The wall is braced from inside or anchored from outside. The bowing wall guide covers those options.
- Minor or shrinkage cracks. Once the wall is cleared as stable, the joints can be repointed. InterNACHI warns that high-strength mortar used on softer mortar can damage the masonry (opens in a new tab), so the new mortar should match the old.
For what drives the price and how to compare quotes, see foundation crack repair cost. If the crack also leaks, ask the engineer when it’s safe to seal it, then see the leaking crack guide.
Who should you call about a stair step crack in a foundation?
An independent structural engineer, before any repair company. The engineer tells you whether the wall is moving and what it needs, and has nothing to sell. Then you can get contractor bids against that report.
The engineer vs contractor guide explains the difference and what to ask. For the width and warning-sign rules for every crack direction, see when to worry about foundation cracks, or start from the foundation cracks hub.
Questions
Are stair step cracks in brick bad?
They mean the same thing as in block: something under that part of the wall has moved. Pillar To Post notes that in block or brick, settlement cracks often follow the mortar joints in a step pattern (opens in a new tab). Look at the foundation directly below the brick crack, and have an engineer check both.
Are stair step cracks normal in a new block foundation?
Some are. InterNACHI notes that block walls can show shrinkage cracks that look like settlement (opens in a new tab), usually in the first year. Report any you find to your builder in writing, check what the warranty covers, and keep a dated photo of each one.
Should I buy a house with stair step cracks in the foundation?
Get a structural engineer's report before you decide, not just the general home inspection. The report tells you whether the crack is old and stable or still moving, and what a repair would involve. How that affects your offer is a question for your agent; the buying and selling guide covers the general picture.
Does homeowners insurance cover stair step cracks?
It depends on your policy and on what caused the crack. Policies can treat settlement differently from sudden damage, so read your policy and ask your agent. The foundation crack insurance guide covers the general questions to ask.