Foundation Cracks: Which Are Normal and Which Aren't

Find a crack in your basement wall and your stomach drops. Relax for a minute: almost every concrete foundation cracks. Concrete shrinks as it cures, and a house settles in its first few years. Most cracks are cosmetic. A few are the house telling you something is moving. Here's how to tell them apart.

01Usually normal

• Thin vertical cracks in poured concrete, often running up from the floor or down from a basement window corner. These are typically shrinkage cracks.
• Hairline cracks you can't fit a credit card into.
• Cracks that are the same width from end to end, with both sides lined up flat.
• Thin cracks in the basement floor slab. Floors crack as they cure, and the slab usually isn't holding up the house.

Even a harmless crack can let water in. If it's dry, seal it and keep an eye on it. If it leaks, it needs a proper repair from the inside or outside.

02Worth a closer look

• Horizontal cracks, especially in concrete block walls. These often mean soil pressure from outside is pushing the wall inward.
• A wall that bows or leans in. Hold a level or a long straight board against it.
• Stair-step cracks following the mortar joints in a block or brick wall.
• Cracks wider than about 1/4 inch, or wider at one end than the other.
• One side of the crack sticking out past the other.
• Cracks that keep growing.

03Signs upstairs that go with it

Foundation movement shows up in the rest of the house too:

• Doors that stick or won't latch, when they used to.
• Windows that suddenly bind.
• Cracks in drywall running from the corners of doors and windows.
• Floors that slope or feel springy.
• Gaps between the trim and the wall or the floor.

One of these alone usually isn't a big deal. Several at once, along with a foundation crack, is worth a professional look.

04Track it yourself

1. Mark the ends of the crack with a pencil line and write the date next to it.
2. Measure the width at its widest point. A cheap crack gauge from the hardware store works, or use a coin or a drill bit as a feeler.
3. Take a photo with a tape measure in the frame.
4. Check it again every month or two, and after big rains and the spring thaw.

If the crack runs past your pencil mark or gets wider, it's moving.

05What causes the bad ones

Most serious foundation problems come down to water and soil:

• Water against the wall. Gutters that dump at the corners, downspouts that end right at the house, and yards that slope toward the house.
• Freeze and thaw in cold climates.
• Expansive clay soil that swells when wet and shrinks when dry.
• Tree roots and poorly compacted fill.

Fix the water first. It's the cheapest repair and the one that stops a lot of cracks from getting worse. See our posts on gutters and downspouts and testing your sump pump.

06Who to call

For a crack that's growing, horizontal, or comes with a bowing wall, call a structural engineer first, not a foundation repair company. The engineer has nothing to sell you; they'll tell you what's wrong and what the fix should be. Then get repair quotes based on their report.

Sources (2)

InterNACHI: Foundation Inspection · InterNACHI: Concrete, Cracking and Water

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