How often should you check your foundation for cracks?

Short answer

Check the foundation for cracks twice a year. On clay soil, or through a drought, check every season, because the soil's movement is what moves the foundation. The check is a walk around the outside and through the basement or crawl space with a flashlight and a tape measure, marking the ends of any crack so you can tell next time whether it grew. It takes 20 to 30 minutes and costs nothing, or $0 to $20 for a tube of filler for hairline cracks.

Why it matters

Every foundation cracks a little. Concrete shrinks as it cures, and a few thin vertical cracks in a basement wall are normal and harmless. The cracks that matter are the ones that grow, that run horizontally or in stair steps along the mortar, or that open wider at one end than the other. Those mean the foundation is moving, and a foundation that moves takes the house with it: doors stick, drywall cracks above the doorways, floors slope, and water finds its way through the gap.

Movement is cheapest to deal with early. A crack that's marked and watched tells you whether it's stable or growing, and a growing crack caught at a quarter inch is a different conversation with an engineer than one caught at an inch. The usual cause is water: gutters dumping beside the foundation, grading that slopes toward the house, or clay soil that swells when wet and shrinks when dry. Most of the fix is outside, in the drainage, and the twice-yearly check is what tells you to look there.

When to do it more often

The index gives one modifier: clay soil or a drought, which means every season. Clay swells in wet weather and shrinks in dry, and a foundation sitting on it rises and falls with the soil. A dry summer that pulls the soil away from the footing is the time a foundation moves most. Beyond that, check after a flood or a burst pipe near the foundation, after nearby excavation, and whenever a door in the house starts sticking for no reason.

What you need

• A flashlight
• A tape measure, to record a crack's width and length
• A pencil, to mark the ends of each crack and the date
• Epoxy or polyurethane crack filler, for hairline cracks that aren't moving

Steps at a glance

1. Walk the outside of the foundation with the flashlight, looking at every exposed face, especially the corners and under the downspouts.
2. Go through the basement or crawl space and look at every wall and the floor slab.
3. For each crack, mark its ends and the date with the pencil, and measure its width at the widest point.
4. Note the direction: vertical, horizontal, diagonal, or stair-stepped along mortar joints.
5. Compare with your marks from last time. A crack that's grown past its marks is moving.
6. Fill hairline cracks that haven't moved with the filler, and photograph anything that's grown or is wider than a quarter inch for an engineer.

You're done when every crack is marked, measured and recorded, and nothing has grown past its last marks.

Signs it's overdue

• A crack wider than a quarter inch, or one that's wider at one end.
• Doors and windows that stick, or that have gaps at the top on one side.
• Cracks in the drywall above doorways, often diagonal.
• Floors that slope, or a marble that rolls on its own.
• Water seeping through a crack.

DIY or pro

The check is an easy job, and the pencil marks are the whole method. A crack filler handles the hairline cracks that aren't going anywhere, and it keeps water out of them. What the filler can't do is stop movement, and a crack that's filled and then opens again is telling you something.

A structural engineer charges $300 to $600 to inspect a foundation and tell you whether the cracks mean movement, what's causing it, and what to do. That's the right call for a horizontal or stair-step crack, for anything wider than a quarter inch, for a crack that's grown past its marks, or for a house with sticking doors and sloping floors. Get the engineer's opinion before a foundation repair company's, since the engineer isn't selling the repair.

Safety

• Structural: a horizontal crack in a basement wall, a wall that bows inward, or a crack that's opening quickly means the wall is under more load than it can take. Don't store heavy things against it, don't dig beside it, and have an engineer look at it soon. A crack that water is coming through will also undermine the soil beneath the footing over time.

FAQ

When should I worry about a foundation crack?

When it's horizontal or stair-stepped, wider than a quarter inch, wider at one end, growing past the marks you made, or letting water in. Thin vertical cracks that don't change are usually shrinkage.

How do I know if a foundation crack is getting worse?

Mark its ends and the date in pencil, and measure its width. Check the marks at the next inspection. A crack that's moved past them is active.

Can I fix foundation cracks myself?

Hairline cracks that aren't moving, yes, with an epoxy or polyurethane filler. Anything that's moving needs the cause fixed, which usually means drainage, and an engineer's advice.

What causes foundation cracks?

Water, mostly. Gutters and grading that put water beside the foundation, and clay soil that swells and shrinks with the weather. Fix the drainage and most movement stops.