How to Tell If a Foundation Crack Is Serious

Read the direction first

• Vertical: most often concrete shrinkage in poured walls. Common, usually a water question rather than a structural one.
• Diagonal, especially from a window or door corner: often differential settlement. Worth measuring.
• Horizontal, particularly mid-height in a block wall: lateral soil pressure. This is the pattern that most warrants professional attention.
• Stair-step through block mortar joints: movement, either settlement or lateral pressure depending on where it widens.

Then measure the width and the offset

Width matters less than most people expect, but it is still evidence. A crack you can slide a coin into is telling you something different from a hairline. What matters more is offset: run a finger across the crack and feel whether one side sits proud of the other. Displacement means the two sides have moved relative to each other, which is a movement signature rather than a curing one.

Then watch it over time

This costs nothing and produces the single most useful piece of evidence any contractor or engineer can be handed. It also protects you from paying to repair something that was never moving.

1. 1Mark each end of the crack with a pencil line and write the date next to it.
2. 2Measure the width at the widest point and note the figure.
3. 3Photograph it with a ruler or coin in frame for scale.
4. 4Repeat after a wet spell and again after a dry one — a full seasonal cycle is ideal.
5. 5If the marks stay put and the width holds, the crack is stable. If either changes, you have documented active movement.

Signs that change the urgency

• Water entering through the crack during rain.
• Doors and windows that have started sticking in the same part of the house.
• Visible bowing or leaning when you sight along the wall.
• A crack that widens noticeably at one end.
• Sloping floors, or gaps opening between floor and baseboard.
• Any of these appearing suddenly rather than gradually.