Horizontal Foundation Cracks
A horizontal crack in a basement or foundation wall is the one type you shouldn't wait on. Here's why, and what happens next.
Bottom line: horizontal cracks in a foundation wall are usually caused by soil pushing the wall inward. Have an independent structural engineer look at one, especially if it's wider than about 1/8", growing, or the wall bows. If the wall is visibly moving, treat it as urgent.
Why horizontal cracks are different
Vertical cracks usually come from concrete shrinking, which doesn't threaten the structure. Horizontal cracks usually come from lateral pressure: wet, expanding or frozen soil outside pushes on the wall until it cracks along a line, often about halfway down or just below ground level. Once a wall has cracked this way, the pressure can keep pushing it inward (bowing).
Common causes
- Hydrostatic pressure: water-saturated soil from poor drainage, clogged gutters or downspouts emptying beside the house
- Expansive clay soil that swells when wet
- Frost heave: frozen soil expanding against the wall in cold climates
- Heavy loads near the wall, such as vehicles, a driveway or backfill compacted during construction
Poured concrete vs. concrete block walls
In poured concrete walls, horizontal cracks are less common, and when they appear they deserve attention. In concrete block walls, pressure often shows as a horizontal crack along a mortar joint, sometimes combined with stair-step cracks at the corners. Block walls can bow noticeably. Check by holding a long straight edge or a taut string against the wall.
Horizontal crack in a basement wall: warning signs
- The wall bows or leans inward at the crack
- The top of the wall has shifted relative to the bottom (shear)
- The crack is wider than 1/8", or getting wider
- Water seeps through after rain
- New stair-step cracks appear at the wall's ends
How horizontal cracks are repaired
Sealing alone doesn't fix a horizontal crack, because the pressure is still there. Common professional fixes, depending on how far the wall has moved, include:
- Carbon fiber straps: bonded to the wall to stop further movement. Typically used when bowing is modest. They hold a wall in place but don't straighten it.
- Wall anchors or braces: steel anchors in the yard, or steel beams braced to the floor joists. Some systems can gradually pull a wall back.
- Excavation and rebuild: for severely displaced walls
- Drainage fixes: gutters, downspout extensions, grading and sometimes exterior drains to reduce the pressure that caused the crack
An engineer's report tells you which of these your wall needs. See foundation crack repair costs for typical price ranges.
What you can do today
- Measure and photograph the crack, and mark its ends with the date.
- Check that gutters are clear and downspouts discharge at least 4–6 feet from the house.
- Check the ground slopes away from the foundation.
- Book an independent structural engineer.