Warning signs

Foundation cracks: what they mean

A crack is the most alarming thing a house can show you and one of the least reliable on its own. Concrete cracks as a matter of course. What turns a crack into information is its shape, its width along its length, where it sits — and above all whether it is still growing.

General information, not an assessment

Nothing here can tell you what a crack in your house means. The same crack carries different weight depending on the wall it is in, how the house was built and what the ground is doing. Only an on-site evaluation establishes that.

Read the taper, not the length

The instinct is to measure how long a crack is. Professionals care far more about whether it is wider at one end than the other.

A crack of even width along its whole length usually reflects material behavior — concrete shrinking as it cured, or two materials expanding at different rates. A crack that tapers, wide at the top and closing to nothing at the bottom or vice versa, reflects rotation: one part of the structure has tipped or dropped relative to another. That is differential movement, and differential movement is what foundation repair exists to address.

The direction of the taper points at the problem. A crack widening toward the top suggests the wall is being pulled apart up there — often a corner dropping away. A crack widening toward the bottom suggests the opposite. Neither is a diagnosis, but both are the kind of detail worth describing when you call someone.

The four patterns, and what each suggests

Four common crack patterns in an exterior wall Four brick wall elevations showing a stair-step crack following the mortar joints, a vertical crack wider at the top, a horizontal crack across the middle of the wall, and a diagonal crack running from the corner of a window opening. Pattern 1 Stair-step follows the mortar joints can indicate differential settlement on one side Pattern 2 Vertical, tapered wider at one end the taper is what matters more than the length Pattern 3 Horizontal across the middle of a wall can indicate lateral soil pressure — get this looked at Pattern 4 From an opening 45° from a window or door very common; concerning mainly if it keeps reopening
None of these patterns is a diagnosis. Brick and mortar crack for many reasons, including normal concrete shrinkage and seasonal movement that never becomes a structural problem. What a professional looks at is the combination: how wide the crack is, whether it tapers, whether it appears alongside sticking doors or out-of-level floors, and — above all — whether it is getting worse over months. Only an on-site evaluation can establish what is happening at a specific address.

Stair-step cracks in brick and mortar

The classic exterior sign of differential settlement. Mortar is deliberately weaker than brick, so a masonry wall under stress cracks along the joints in a staircase pattern rather than splitting the bricks. Most common near corners and above openings, because those are where the wall is weakest.

What to note: which end is wider, whether it continues below the brick line, and whether the wall has moved out of plane — sight along it from the corner and see whether it still looks straight.

Vertical cracks

Common and frequently benign. In poured concrete, vertical cracks appear from normal curing shrinkage, especially within the first couple of years and often near the middle of a wall or at a form joint. They become interesting when they taper noticeably, when they leak, or when they keep widening.

Horizontal cracks

The one to take seriously. A horizontal crack along a wall generally indicates lateral pressure — soil pushing inward — rather than the vertical movement everything else on this page describes. On a basement or retaining wall it often appears alongside visible bowing and is the most time-sensitive symptom covered on this site. More on bowing walls →

Diagonal cracks from door and window corners

Openings interrupt a wall, so stress concentrates at their corners and cracks radiate out at roughly 45 degrees. Short hairlines here are among the most common findings in any house and are usually cosmetic. The version worth attention is one that keeps reopening after patching, or one accompanied by the door itself no longer closing — which is its own signal .

Slab cracks specifically

If you can see the slab — in a garage, or under lifted flooring — you will almost certainly find cracks, and most of them are shrinkage. Concrete loses volume as it cures and a slab of any size relieves that stress by cracking somewhere. Control joints exist to decide where.

Slab cracks become interesting when there is vertical displacement: run a finger across and feel whether one side sits higher than the other. A flat crack is a crack. A crack with a lip is a report of movement, and it is worth getting floor elevations measured across the whole floor plan rather than judging by that one spot.

The measurement that settles it

Photograph the crack with a coin or tape measure beside it. Write the date on the photo. Do it again in three and six months.

That is the entire method, and it answers the only question that really matters. Contractors and engineers do a more rigorous version — floor elevation surveys, sometimes crack monitors glued across the gap with a vernier scale — but the homeowner version is genuinely useful and costs nothing. A crack that has not changed in six months is behaving very differently from one that has.

A Texas-specific caution

Expansive clay moves seasonally, so cracks here open in late summer and close again after a wet spring. A crack measured only in September against a photo from May can look alarming when it is actually the normal annual cycle. Comparing the same month across two years tells you more than comparing seasons within one. More on why Texas foundations move →

What a repair costs, if one is needed

Sealing a non-structural crack by epoxy or polyurethane injection is a job of a few hundred dollars per crack and is a complete repair, not a patch, when the crack is not a symptom of movement. If the elevations show the slab has actually dropped, the crack is the report rather than the problem and the work is structural. Full cost guide →

Questions about foundation cracks

How wide does a foundation crack have to be before it matters?

Width is a useful signal but a poor threshold, and anyone quoting you a single number is oversimplifying. As rough orientation: hairline cracks you can barely catch a fingernail in are extremely common and usually cosmetic; cracks around an eighth of an inch are worth photographing and watching; cracks wide enough to slide a nickel into generally get a professional's attention. But a hairline crack that has doubled since spring is more interesting than a quarter-inch crack that has not moved in a decade. Change over time beats width at any single moment.

Are vertical or horizontal cracks worse?

Horizontal, almost always. A vertical or diagonal crack generally reflects vertical movement — settlement or heave — which is a serious but familiar problem with well-understood fixes. A horizontal crack running along a wall usually reflects lateral pressure pushing the wall inward, which is a different failure mode and can progress faster. On a basement or retaining wall in particular, a horizontal crack is the one to have looked at soon rather than eventually.

What is a stair-step crack?

A crack that climbs diagonally through the mortar joints of a brick or block wall, stepping along the horizontal and vertical joints rather than passing through the units themselves. It happens because mortar is weaker than brick, so when one part of a wall drops relative to another the crack takes the path of least resistance. It is the most recognizable exterior symptom of differential movement — one part of the house settling more than another — and its width at each end tells you which part dropped.

Are cracks in a new house normal?

Very. Concrete shrinks as it cures and nearly every slab develops hairline cracking within a year or two — that is shrinkage, not settlement, and it is not a defect. New houses also settle as the soil under them compresses and the framing dries, which produces drywall cracks at the corners of door and window openings. What is worth attention in a newer home is a crack that keeps reopening after repair, or one that appears alongside sticking doors, because that suggests something is still moving. Also check whether your builder's structural warranty is still live — many run ten years.

Should I fill the crack myself?

Only after you have photographed and dated it. Filling a crack destroys the evidence of whether it is moving, which is the single most valuable piece of information about it. If it is cosmetic, sealing it is fine and epoxy or polyurethane injection by a professional is a complete repair for a non-structural crack. If it is a symptom of movement, filling it treats the report rather than the problem and the crack comes back — at which point you have lost six months of useful observation.

Do cracks mean my foundation needs replacing?

Essentially never. Full foundation replacement is extraordinarily rare and almost always the wrong answer; the overwhelming majority of foundation problems are addressed by adding support underneath the existing foundation, correcting drainage, or both. If anybody tells you a slab needs to be torn out and repoured because of cracking, that is the point at which to stop and pay for an independent structural engineer's opinion before agreeing to anything.

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Find out whether it's moving

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