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Most foundation cracks are thin vertical shrinkage cracks in poured walls, usually under 1/8 inch, and the fix is sealing them if they leak. Horizontal cracks, stair-step cracks in block, cracks over 1/4 inch and cracks with offset edges are different: have an engineer look before you repair anything. The direction of a crack tells you more than its width.
What do the different foundation crack types mean?
The direction of the crack is the first clue. Vertical and window-corner diagonal cracks in poured concrete are usually shrinkage. Horizontal cracks and stair-step cracks in block usually mean the soil is pushing on the wall or the footing has moved.
| Crack you see | Usual cause | How concerned to be | Next step |
|---|---|---|---|
| Vertical, poured wall, under 1/8 inch | Shrinkage as the concrete dried | Low | Seal it if it leaks. Vertical cracks |
| Diagonal from a window or door corner | Shrinkage at the corner of the opening | Low | Same as vertical |
| Vertical or diagonal, 1/8 to 1/4 inch | Settlement or shrinkage | Watch it | Monitor it for growth |
| Horizontal, below grade | Soil, water or frost pressure from outside | High | Horizontal crack guide, then an engineer |
| Stair-step in a block wall | Footing settlement or soil pressure | High | Stair-step crack guide, then an engineer |
| Any crack with offset edges | Shear movement in the wall | High | Engineer |
| Wider than 1/4 inch, or growing | Ongoing movement | High | Engineer |
Sources: NRMCA CIP 7 (opens in a new tab), Pillar To Post (opens in a new tab), ASHI Reporter (opens in a new tab).
A classic shrinkage crack has a profile. Pillar To Post’s inspectors describe it as vertical, usually under 1/8 inch, and in the middle third of the wall (opens in a new tab), staying in the foundation rather than running up through the house. A crack near the end of a wall is less likely to be shrinkage.
Stair-step cracks follow the mortar joints in a block wall (opens in a new tab), so they look like a staircase. In poured concrete, the same movement shows up as a vertical or diagonal crack instead.
What causes foundation cracks?
Four things crack foundations: shrinkage, settlement, soil and water pressure, and frost. Shrinkage happens to almost every poured wall and is cosmetic. The other three involve the wall or footing moving, and that movement is what you’re judging.
- Shrinkage. Concrete is at its largest the day it’s poured. As it dries it shrinks, and when the footing and floor hold it in place, it cracks (opens in a new tab). The diagonal cracks that run from window and door corners are shrinkage cracks too.
- Settlement. When the soil under part of the footing compresses or washes out, that section drops. The NRMCA puts it as non-uniform support of footings (opens in a new tab). Pillar To Post notes that most settlement is short-term, and ongoing settlement is unlikely and uncommon (opens in a new tab).
- Soil and water pressure. Wet soil outside a basement wall pushes inward. ASHI’s Tom Feiza names wet soils, poor maintenance of surface water and frost (opens in a new tab) as the causes of horizontal cracks.
- Frost. Frozen soil expands and pushes on the wall from outside, the same direction as wet-soil pressure.
Backfilling can also crack a new wall. The NRMCA notes this happens during backfill, especially when heavy equipment gets too close or the wall is not yet supported the way the design intends.
If you’re asking “why is my foundation cracking now,” look outside first. Gutters that dump at the corner, soil that slopes toward the house and a wet season all raise the pressure on the wall. The NRMCA recommends a finish grade that slopes 1/2 to 1 inch per foot for at least 8 to 10 feet (opens in a new tab) away from the foundation.
How wide is too wide for a crack in a foundation wall?
Under 1/8 inch is typical shrinkage. Over 1/4 inch is the point where builders’ guidelines say a basement wall crack needs repair, and where you should get an engineer’s opinion. Between the two, watch whether it grows.
There is no single rule. An NAHB presentation by a warranty company engineer says outright that there is no absolute universal standard for evaluating cracks (opens in a new tab). The thresholds you’ll see come from different places:
| Source | What it says | Width |
|---|---|---|
| NRMCA CIP 7 (opens in a new tab) | A typical new-home warranty requires repair when a basement wall crack leaks, has vertical displacement, or exceeds this width | 1/8 inch (3 mm) |
| NAHB performance guidelines (opens in a new tab) | Concrete basement wall and masonry wall cracks wider than this need correction | 1/4 inch |
| Pillar To Post (opens in a new tab) | Settlement cracks with a total opening under this are probably not ongoing settlement | 1/4 inch |
Width only matters when the crack simply opened. If one side has shifted past the other, in or out or up or down, Pillar To Post notes that the quarter-inch rule does not apply (opens in a new tab) and it can be a significant structural concern. A crack you repaired that has opened again is also a sign of ongoing movement.
The when to worry guide shows how to measure width without special tools and how to tell if a crack is getting bigger.
Is it a crack or a pour line?
A long, roughly level line that runs the length of a poured wall may be a pour line, not a crack. It’s where one load of concrete met the next, and the NRMCA lists pour lines and cold joints among the things often perceived as cracks (opens in a new tab).
A pour line usually wanders gently and has a slightly different texture or color above and below. A horizontal crack is a sharp break, and the wall may lean in along it. If you can’t tell, treat it as a horizontal crack until someone qualified has looked.
Which foundation cracks can you fix yourself?
Vertical and diagonal cracks in a poured concrete wall, under 1/4 inch, with edges that line up and a wall that’s straight. Those are the cracks injection kits are made for, and sealing them from inside is a normal DIY job. Everything else on this page needs an engineer before any repair.
Injection seals a crack against water and soil gas. It doesn’t hold back a wall that’s moving. That’s why the foundation crack repair guide starts with the checks above, and the injection guide walks through the job.
Polyurethane foam is the usual choice for a leaking crack because it expands and works in a damp crack. Epoxy bonds the two sides together but needs a dry crack. The epoxy vs polyurethane comparison explains when each one fits.
The same kit comes with a peel-off surface sealer if the wall will stay exposed and you want a clean finish, and in a 30 ft size for several cracks. Before you buy, check that your crack is on the safe list. A sealed crack in a moving wall just cracks again next to the repair.
When should you call an engineer about a foundation crack?
Call a structural engineer for a horizontal crack, a stair-step crack in block, a crack over 1/4 inch, edges that are offset, a wall that bows or leans, or a crack that keeps growing. Those match the warning signs in the NAHB presentation, which lists horizontal basement wall cracks, especially with bowing or leaning (opens in a new tab), cracks with vertical displacement and large separations.
An independent engineer tells you what’s wrong and what the fix should be, without selling the fix.
A repair contractor’s free inspection ends in a quote. The engineer vs contractor guide covers what each costs and what to ask. For a wall that’s already moving inward, see bowing basement walls.
Every guide in this section
Is it a problem?
- When to worry about foundation cracks
- Horizontal crack in basement wall
- Vertical foundation cracks
- How to monitor a crack
- Stair-step and diagonal cracks
- Bowing basement walls
How to fix it
- Foundation crack repair
- Basement wall crack repair
- Leaking basement wall crack
- Foundation crack injection guide
- Injection troubleshooting
Cost, insurance and who to call
- Foundation crack repair cost
- Does insurance cover foundation cracks
- Engineer vs contractor
- Selling or buying a house with a foundation crack
Related problems
Questions
Is it normal to have cracks in a foundation?
Yes. The concrete industry's own guidance says some cracking is normal in concrete basement walls (opens in a new tab), mostly from shrinkage as the concrete dries. What isn't normal is a crack that runs horizontally, has offset edges, or keeps getting wider.
Can I fix a foundation crack myself?
You can seal a vertical or diagonal crack in a poured wall yourself with an injection kit, as long as it is under 1/4 inch, the edges line up and the wall is straight. Anything on the engineer list (horizontal, stair-step in block, offset, bowing) is not a DIY job, because sealing it doesn't stop the movement behind it.
Does homeowners insurance cover foundation cracks?
Usually not for cracks from settling, shrinkage or soil pressure, which many policies exclude. Some policies cover cracks caused by a sudden covered event. Read your policy and ask your agent; the foundation crack insurance guide covers what to ask.
How much does it cost to fix a foundation crack?
It depends on the crack. Sealing a single non-structural crack costs far less than stabilizing a wall that has moved. The foundation crack repair cost guide gives DIY kit prices, explains what drives contractor and engineer costs, and lists what a quote should include.