Almost every concrete foundation cracks at some point. Most cracks are harmless; some are early signs of a serious problem. Here's how to tell the difference.
Usually normal: thin vertical shrinkage cracks
Poured concrete shrinks as it cures, and thin vertical cracks, often running from the top of the wall or from a window corner, are common. If a crack is hairline to about 1/8 inch wide, isn't getting wider, and doesn't leak, it's usually cosmetic. If it leaks, it can typically be sealed with injection.
Worth a closer look: cracks that are widening or offset
A crack that has grown since you first noticed it, is wider at one end, or where one side has shifted relative to the other suggests the foundation is moving. Mark the ends of the crack with a pencil and the date, or use a crack gauge, and check again in a few weeks.
Call a pro: horizontal and stair-step cracks
A horizontal crack along a block or poured wall, especially with the wall bowing inward, usually means soil pressure from wet or frozen soil. Stair-step cracks in block or brick can indicate settlement. These deserve an evaluation by a foundation repair specialist or structural engineer.
Signs elsewhere in the house
Doors and windows that stick, cracks in drywall above doors, sloping floors and gaps between walls and ceilings can all point to foundation movement. A floor-level survey helps pinpoint where.
Water is often the cause
Many foundation problems start with water: downspouts dumping at a corner, poor grading, or saturated clay soils. Fixing drainage is part of a lasting repair. See how pros handle foundation repair in New York communities.
This article is general information, not professional advice. Dawn Waterproofing connects homeowners with independent local service providers and does not perform the work.