Short answer: it depends on which wall
A horizontal crack can mean very different things depending on where it is. On an interior drywall or plaster wall, it is often a minor issue such as a failing tape joint. On a basement, crawlspace or other foundation wall, a horizontal crack is generally treated as more serious, because it can indicate that soil or water outside is pushing the wall inward. Because the second case can involve structural safety, it is sensible to have it assessed rather than guess.
Horizontal cracks in drywall or plaster walls
On upper-floor or ordinary interior walls, a thin horizontal crack is frequently caused by:
- Drywall tape or joint failure. Horizontal seams between sheets, or the seam near the ceiling, can open as the building shifts slightly with humidity and temperature. Poor taping is covered in signs of bad drywall installation.
- Seasonal movement. Framing can swell and shrink a little through the year.
- Settling in newer homes. Small movements as materials dry out can open fine lines.
These are usually cosmetic when the crack is thin, stable and not accompanied by other symptoms. For general triage across all directions, see our guide to interior wall cracks.
Take it more seriously if the crack is wide, the wall looks bowed, or the crack lines up with a horizontal crack on the exterior or in the basement below.
Horizontal cracks in basement and foundation walls
A horizontal crack running along a block or poured concrete foundation wall is a recognised warning sign. It is commonly associated with lateral pressure from soil, often made worse by water. Signs that raise the level of concern include:
- The wall bowing or leaning inward, or one side of the crack sitting out of line with the other.
- A crack that has grown or that is wider than about 1/4 inch.
- Water seeping through the crack, or efflorescence (white mineral deposits) nearby.
- Stair-step cracks in block mortar joints near the ends of the wall.
- Sticking doors, uneven floors or cracks elsewhere in the house.
If you see a horizontal crack together with bowing in a foundation wall, avoid piling storage against it, do not try to fix it yourself, and contact a structural engineer or a qualified foundation specialist. Be cautious about the first contractor’s quote; a second opinion, ideally from an engineer who does not sell repairs, can help.
What causes horizontal wall cracks
- Hydrostatic pressure. Wet soil against a foundation wall adds load. Poor drainage, clogged gutters, or grading that slopes toward the house can contribute.
- Expansive or frozen soil. Clay soils that swell when wet, or frost, can push on walls.
- Heavy loads near the wall. Vehicles, or soil piled against it, add pressure.
- Structural movement. Foundation settlement or shifting can crack walls in various directions.
- Non-structural causes. Tape failure in drywall, or moisture-swollen wall materials.
How to tell if a crack is structural
No single sign is definitive, but taken together these help:
- Location. Foundation, basement and masonry walls are higher concern than a drywall seam.
- Width and growth. Measure it, date it, and re-measure over weeks and seasons.
- Alignment. Is one side of the crack displaced or pushed in relative to the other?
- Bowing. Hold a straight edge or string line along the wall to check for bulges.
- Companion symptoms. Sticking doors and windows, sloping floors, other cracks, or water.
If you are unsure, photograph the crack with a ruler for scale and ask a professional to review it.
What to do first
- Take dated photos and measurements.
- Check outside for obvious water issues: downspouts that dump next to the foundation, soil sloping toward the house, standing water. If the crack is damp, see water leaking through a foundation or basement and a foundation crack leaking water.
- Direct downspouts away from the house and keep gutters clear. This is a reasonable low-risk step, though it will not fix existing damage.
- For a foundation wall crack, contact a structural engineer or reputable foundation specialist instead of patching and forgetting.
- For a minor drywall crack, a tape-and-compound repair is a normal DIY job; if it reopens, investigate further.
How horizontal foundation cracks are repaired
Repair depends on the wall and the cause, and should be specified by a professional. Methods commonly described include carbon fiber straps for walls with limited inward movement, wall plate anchors or steel braces, and helical tiebacks or excavation for more serious cases. Improving drainage often forms part of the solution. Epoxy or polyurethane injection may seal a crack against water but does not by itself resist soil pressure. For concrete patching of minor cracks, see how to repair a crack in a concrete wall. Outdoors, a similar pattern on a freestanding wall is covered in crack in a retaining wall.
FAQ
What to do about foundation cracks?
Document them, check drainage, monitor for growth, and have a structural engineer or foundation specialist assess any horizontal, wide or growing crack.
What do stress cracks look like?
They are often diagonal, stair-step or horizontal, wider at one end, and may come with displaced edges. Hairline cracks from shrinkage are generally random and thin.
How do I tell if a drywall crack is structural?
Look at the direction, width, growth and other symptoms. A thin, stable crack along a seam is typically cosmetic. A wide, growing crack with sticking doors, sloping floors or bowing walls justifies a professional look.