A crack in your foundation is a break in the concrete, block or brick that carries your house down to the soil. Most foundation cracks are harmless shrinkage that forms as concrete dries. A few point to soil movement, water pressure or a settling footing, and those need an engineer before they grow. The hard part is telling the two apart, and the clues are in the crack's direction, width, offset and growth over time.
If you found a crack in your basement wall, slab or crawl space, you need a clear answer to one question: is this serious? You are not alone: NAHB reports that cracks are the top concern homeowners raise when they call a builder's warranty team with structural questions, and that most cracks are cosmetic. In this guide I will explain what causes foundation cracks, what each pattern means, how wide is too wide according to published standards, how to measure and monitor a crack, which repair fits which crack, and what the repairs cost in 2026.
Short answer
A thin vertical crack in a poured concrete wall, with both sides level and no growth, is almost always shrinkage. Seal it if it leaks. A crack becomes a concern when it is horizontal, wider than about 1/4 inch, offset so one side sits higher or further out, paired with a bowing wall, or still growing after a few months. NAHB guidance treats those as signs of a potential structural problem that needs a professional engineer.
Usually fine
Hairline to 1/8 inch
Vertical or slightly angled, even width, no offset, no water and no change over time.
Measure and monitor
1/8 to 1/4 inch
Diagonal or stair-step cracks, slow seepage, or a crack wider at one end than the other.
Call an engineer
Over 1/4 inch or moving
Horizontal cracks, offset edges, a bowing wall, sticking doors, or any crack that keeps growing.
What Is a Foundation Crack?
A foundation crack is any separation in a footing, foundation wall or concrete slab. Engineers sort them into two groups. A cosmetic crack, also called a non-structural crack, comes from the material itself shrinking or moving with temperature, and it does not weaken the foundation. A structural crack comes from forces acting on the foundation, such as settling soil or pressure from outside, and it can keep growing until the wall or footing loses support.
Cracks are normal in concrete. A 2018 risk management presentation by the National Association of Home Builders (NAHB) puts it plainly: cosmetic cracks develop in every new home, and the vast majority of cracks are cosmetic, not structural. The same presentation notes that conventional spread footings are designed to tolerate up to about 1 inch of movement. Some cracking is simply the foundation doing its job.
Why Do Foundations Crack?
Every crack has a cause, and the cause decides the fix. Below I am sharing the main causes, from the most common and least worrying to the least common and most serious.
- Drying shrinkage: Fresh concrete holds a lot of water. As that water leaves, the concrete shrinks and cracks, usually in the first year or two. The wetter the original mix, the more shrinkage cracking you get.
- Temperature changes: Concrete expands in heat and contracts in cold. NAHB's figures show a 100-foot exterior concrete wall moving about 1/2 inch across a 75°F temperature swing.
- Uneven settlement: When soil under one part of a footing compresses or washes out more than under the rest, that part drops. The result is a diagonal or stair-step crack, often wider at the top. Our guides to settling and subsidence explain how to tell normal settling from a footing problem.
- Expansive clay: Clay soils swell when wet and shrink when dry, lifting and dropping the foundation with the seasons. This causes cracks that open and close through the year.
- Soil and water pressure: Saturated soil, frost and hydrostatic pressure push sideways on basement walls. Block walls crack horizontally along a mortar joint and bow inward.
- Other loads: Tree roots, a leaking pipe that softens the soil, heavy equipment near the wall, or an earthquake can all crack a foundation that was otherwise sound.
Types of Foundation Cracks and What They Mean
The direction of a crack tells you which way the force acted. Below I am explaining each common crack type, where you usually find it, its usual cause and how much concern it deserves, in a table.
| Crack type | Where you see it | Usual cause | Concern |
|---|---|---|---|
| Hairline vertical | Poured concrete walls, often near windows or mid-wall | Drying shrinkage | Low; seal if it leaks |
| Diagonal | Poured walls, often from a corner or window | Uneven settlement of the footing | Medium; measure and monitor |
| Stair-step | Block or brick walls, along mortar joints | Settlement at a corner, or soil pressure | Medium to high, higher if the wall bows |
| Horizontal | Block walls, often near mid-height or just below grade | Soil, water or frost pressure from outside | High; call an engineer |
| Slab crack | Basement floor or slab-on-grade | Shrinkage, or heave and settlement | Low unless offset or wide |
| Crack with offset | Any wall or slab | One side moved relative to the other | High at any width |
As the table shows, direction is the first clue. Vertical cracks are usually shrinkage, while horizontal cracks and any crack with an offset point to forces acting on the wall.
The glossary entry for stair-step cracks explains why block walls crack along their mortar joints instead of through the blocks.
How Wide Is Too Wide for a Foundation Crack?
There is no single legal limit for crack width. NAHB itself notes that no absolute universal standard exists for evaluating cracks. What does exist are published thresholds from builder performance guidelines and engineering practice. Below I am explaining the most useful ones in a table.
| Source | Element | Threshold | What it means |
|---|---|---|---|
| NAHB Residential Construction Performance Guidelines | Concrete basement wall | Wider than 1/4 in. | Builder repairs it under warranty |
| NAHB Residential Construction Performance Guidelines | Concrete floor slab | Wider than 3/16 in. | Builder repairs it under warranty |
| NAHB Residential Construction Performance Guidelines | Footing, masonry wall or mortar joint | Wider than 1/4 in. | Builder repairs it under warranty |
| Engineering scale (R. W. Day, cited by NAHB) | Any crack | Hairline to 1/8 in. | Negligible to slight |
| Engineering scale (R. W. Day, cited by NAHB) | Any crack | 3/16 to 9/16 in. | Moderate |
| Engineering scale (R. W. Day, cited by NAHB) | Any crack | 9/16 to 1 in., or more | Severe to very severe |
As the table shows, the published limits cluster between 1/8 and 1/4 inch. Below that range, cracks count as negligible; above it, builders repair them and engineers start to rate them moderate or worse.
Width alone does not settle the question. A 1/16-inch crack where one side has shifted outward is more serious than a straight 1/8-inch shrinkage crack, because the offset proves the wall has moved. Always look at width, direction, offset and growth together.
So, Is Your Foundation Crack Serious? Signs to Check
NAHB's guidance lists the indications of a potential structural crack. Below I am sharing them, with what each one looks like in a house.
- Large cracks and separations: Cracks past about 1/4 inch, or gaps where a wall has pulled away from a floor, chimney or adjoining wall.
- Floor deflection or tilt: A floor that slopes noticeably, so a ball rolls to one side of the room.
- Doors and windows that stop working: Doors that stick, swing on their own or show tapered gaps at the top.
- Walls that slope, bow or lean: A basement wall that curves inward, or a wall that is out of plumb.
- Cracks with vertical displacement: One side of the crack sits higher or lower than the other.
- Horizontal basement wall cracks: Especially with bowing or leaning, because they point to soil pressure.
Two more checks matter for your health and your basement. Water through a crack brings damp and mold, so seal leaking cracks even when they are cosmetic. The EPA's radon guidance also lists cracks in floors and walls among the ways radon gas enters a home; if you live in a radon-prone area, test before and after any crack repair.
How to Measure and Monitor a Foundation Crack
A single look at a crack tells you its size. Monitoring tells you whether it is moving, and movement is what separates a stable crack from an active one. Below I am sharing the steps.
- Clean and light the crack: Brush off loose paint and dust, and use a flashlight held at a low angle so the edges cast a shadow.
- Measure the width: Use a crack-width card, a feeler gauge or a ruler marked in millimeters. Measure at the widest point and record it.
- Check for offset: Run a straightedge across the crack. If one side sits higher or further out, note by how much.
- Mark the ends: Draw a short pencil line across each end of the crack and write the date. New growth past the line is easy to see.
- Fit a crack monitor: A plastic tell-tale gauge glued across the crack shows movement in two directions to a fraction of a millimeter.
- Photograph it: Take the same photo, from the same spot, with a ruler in view, each time you check.
- Repeat monthly for three to six months: Cover at least one wet and one dry season if you can, because clay soils move with moisture.
Use this simple formula to turn your readings into a growth rate:
Growth rate = (latest width − first width) ÷ months between readings
Example: A crack measured at 2.0 mm in March and 3.5 mm in September grew 1.5 mm in 6 months, a rate of 0.25 mm per month. Any steady growth like that means the cause is still active, so the crack needs an engineer's assessment, not just a sealant. A crack that opens slightly in summer and closes in winter, with no overall growth, is usually seasonal movement.
How Are Foundation Cracks Repaired?
The repair has to match the cause. Sealing a crack only stops water; it does not stop a wall from moving. Below I am explaining the common repairs, what each one fixes and the typical 2026 cost from This Old House's cost data, in a table.
| Repair | What it fixes | Typical cost |
|---|---|---|
| Crack sealing or injection | Leaking or cosmetic cracks in poured walls; epoxy bonds the crack, polyurethane stays flexible to stop water | $250–$800 per crack |
| Wall reinforcement | Bowing walls, using carbon fiber or steel strips fixed to the wall | $4,000–$12,000 for about 12 strips |
| Piering or underpinning | Footings that keep settling, using steel or concrete piers to firmer soil | $1,000–$3,000 per pier |
| Drainage and grading | Water pressure and saturated soil that cause the cracking | Varies with scope |
| Structural engineer's report | Diagnoses the cause and specifies the repair | $500–$1,000 |
As the table shows, sealing is the cheapest repair, but it only stops water. Bracing and piers cost far more because they stop movement.
This Old House puts the average foundation repair at about $5,179, with most homeowners paying $2,224 to $8,134. For a deeper comparison of piers, anchors, straps and injection, see our hub of foundation repair methods compared.
Who Should Inspect a Foundation Crack?
Three kinds of professionals look at foundation cracks, and they do different jobs. Below I am sharing who to call and when.
- Home inspector: Notes visible cracks during a purchase inspection. An inspector flags problems but does not diagnose structural causes or design repairs.
- Structural engineer: Measures the cracks, may run a floor elevation survey, identifies the cause and writes a repair specification. Call one for any crack that shows the warning signs above.
- Foundation repair contractor: Carries out the repair. Many offer free inspections, but a free inspection from the company selling the repair is not an independent opinion.
The safest order is engineer first, contractor second. An engineer's report lets you compare quotes against the same scope, and it gives you a record of the repair when you sell the house.
Foundation Cracks When Buying or Selling a House
A foundation crack does not have to stop a sale, but it changes the conversation. If you are buying, ask the sellers for any engineer's reports, repair invoices and transferable warranties, and get your own engineer's opinion on any crack that shows the warning signs. If you are selling, disclose known cracks and past repairs according to your local disclosure rules, and keep the paperwork. Our home inspection and buying guides cover the steps in detail.
Common Mistakes to Avoid With Foundation Cracks
- Sealing before measuring: Caulk hides the width and the growth marks. Measure and photograph first.
- Judging by width alone: A narrow crack with an offset is more serious than a wider straight one.
- Patching a moving wall: Injection does not stop a bowing or settling wall. Fix the force, then seal the crack.
- Ignoring the outside: Gutters that dump water at the wall and soil that slopes toward the house cause many cracks. Fix drainage as part of any repair.
- Relying only on a contractor's free inspection: Get an independent engineer when the repair is structural.
- Losing the paperwork: Keep every report, invoice and warranty. Buyers and their lenders will ask.
Conclusion
Most foundation cracks are shrinkage, and the right response is to measure them, seal them if they leak and keep an eye on them. The cracks that matter are horizontal, offset, wider than about 1/4 inch, paired with a bowing wall or sticking doors, or still growing. For those, get a structural engineer to find the cause before anyone sells you a repair. For more help, browse our independent, engineer-checked foundation guides, and check your local building department and builder warranty for the rules that apply to your home.
Frequently Asked Questions
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Can a cracked foundation be repaired?
Yes. Most cracked foundations are repaired, not replaced. A shrinkage crack that leaks is sealed with an epoxy or polyurethane injection. A wall that bows is braced with carbon fiber strips, steel beams or wall anchors. A footing that keeps settling is supported with piers. Replacement is rare and only needed when a wall has moved so far that bracing cannot hold it.
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Will homeowners insurance pay for a cracked foundation?
Usually not. Standard homeowners policies exclude cracking caused by settling, shrinking, soil movement and gradual water damage. Coverage generally applies only when a sudden, accidental event damages the foundation, such as a fire, a gas explosion or a vehicle impact. Read the exclusions section of your own policy, and ask your insurer before you file a claim.
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Is it expensive to fix a cracked foundation?
It depends on the cause. This Old House's 2026 data puts sealing or injecting a crack at $250 to $800. Bracing a bowing wall with steel or carbon fiber runs $4,000 to $12,000, and piers cost $1,000 to $3,000 each. The average foundation repair is about $5,179. A structural engineer's report costs $500 to $1,000 and stops you paying for the wrong fix.
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What should I do if I find a crack in my foundation?
Photograph it with a ruler for scale, measure its width at the widest point, and mark both ends with a pencil and the date. Check whether one side has shifted, whether the wall bows, and whether doors nearby have started to stick. Then recheck every month. Call a structural engineer straight away if the crack is horizontal, wider than 1/4 inch, offset or growing.
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Is it normal to have a crack in a new foundation?
Yes. Concrete shrinks as it dries, so fine vertical cracks often appear in the first year or two. The National Association of Home Builders states that cosmetic cracks will develop in every new home. Its performance guidelines treat a basement wall crack as a builder repair item only when it is wider than 1/4 inch. Report any crack to your builder within the warranty period.
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Is it better to fix foundation cracks from inside or outside?
Inside repairs are the usual choice for a leaking shrinkage crack, because injection seals the crack through the full wall thickness without digging. Outside repairs mean excavating down to the footing, which costs more but lets the crew add a membrane and fix drainage at the same time. Pick outside work when water pressure or poor drainage is the real cause.
Sources and Standards
- National Association of Home Builders, Construction Liability and Risk Management Committee, W. Keaveny, PE, Misconceptions about the common crack, January 2018.
- National Association of Home Builders, Residential Construction Performance Guidelines (thresholds as cited in the presentation above).
- BRE Group, Assessing cracks in houses, and BRE Digest 251, Assessment of damage in low-rise buildings.
- US EPA, A citizen's guide to radon, and Health risk of radon.
- This Old House, Foundation repair cost, updated October 2026.
- Nationwide, Does homeowners insurance cover foundation repair?
- Standards Australia, AS 2870, Residential slabs and footings (Appendix C, damage classification).