Cracks in Walls: When to Worry (and When It's Normal)

Most cracks in walls are normal and harmless. Thin, straight hairline cracks usually come from the house settling or from building materials shrinking and swelling with the seasons. You should worry more about cracks that are wider than about 1/4 inch, run diagonally, follow a stair-step pattern, keep growing, or show up with sticking doors or sloping floors. Those can point to foundation movement or water problems.

This guide helps you tell the difference, measure and track a crack, and know when it is time to call a pro.

Quick guide: normal or worrying?

Why walls crack

Houses are always moving a tiny bit. Here are the most common reasons:

• Normal settling. New homes settle into the soil over the first few years. Small cracks are very common during this time.
• Humidity and temperature changes. Wood framing and drywall swell in damp weather and shrink in dry weather. This opens and closes small cracks with the seasons.
• Poor taping. Drywall seams that were not taped well can crack along straight lines.
• Heavy loads. A heavy piece of furniture, a new second-floor bathroom, or a big bookcase can stress a wall.
• Foundation movement. Soil that shrinks, swells, or washes away can make part of the foundation sink or lift.
• Water. Leaks, poor drainage, and gutters that dump water next to the house can soften the soil under your foundation. Hidden leaks inside walls can also damage drywall. Our guide on warning signs of a hidden water leak shows what to look for.

Hairline cracks: usually cosmetic

Hairline cracks are very thin, often about the width of a hair or a credit card edge. They are usually straight or slightly wavy and often start at the corner of a door or window.

These are common in almost every house. If they are not getting bigger, you can simply patch and paint them.

Diagonal cracks: pay attention

Diagonal cracks that run at an angle from the corners of doors and windows can mean one part of the house is settling faster than another. Thin ones may still be normal. Wide ones, or ones that keep growing, need a closer look.

Stair-step and horizontal cracks: call a pro

• Stair-step cracks follow the mortar lines in brick or block walls, like a staircase. They often point to foundation movement.
• Horizontal cracks in basement or foundation walls can mean soil is pushing the wall inward. This is one of the more serious types of cracks.

For either one, get a structural engineer or foundation expert to inspect.

Other warning signs that go with bad cracks

A crack alone is not always a problem. But be concerned if you also notice:

• Doors or windows that suddenly stick or will not close
• Gaps between walls and the ceiling or floor
• Floors that slope or feel bouncy
• Cracks in the foundation or in brick outside
• Walls that bulge or lean
• Water stains or damp spots near the crack

How to measure and track a crack

Tracking a crack for a few weeks tells you if it is stable or growing.

1. Measure the width with a ruler or a crack width card. A coin can help too. A dime is a little thicker than 1/32 inch.
2. Mark the ends of the crack with a pencil and write the date next to each mark.
3. Take a photo with a ruler next to the crack.
4. Check again every 2 to 4 weeks. Measure and take a new photo.

If the crack gets longer or wider, it is still moving. That is a good time to call a pro.

How to fix small, stable cracks

If a crack is thin and not growing, you can patch it yourself.

1. Widen the crack slightly with a utility knife so the filler has something to grip.
2. Clean out dust with a brush.
3. Apply mesh drywall tape over the crack for larger cracks.
4. Spread joint compound over it with a putty knife. Let it dry.
5. Sand lightly and add a second thin coat if needed.
6. Prime and paint to match the wall.

For cracks that open and close with the seasons, a flexible, paintable caulk may last longer than regular spackle.

Control moisture to prevent cracks

Big swings in humidity make walls move. Keeping indoor humidity steady, ideally between 30 and 50 percent, helps. Too much moisture can also lead to condensation and mold. If your home feels damp even with the AC running, see our guide on why a house stays humid with the AC on. In winter, watch for water on the inside of your windows.

Outside, keep gutters clean and make sure downspouts send water at least a few feet away from your foundation.

When to call a pro

Call a structural engineer or foundation specialist if:

• A crack is wider than about 1/4 inch
• A crack keeps growing over a few weeks
• You see stair-step or horizontal cracks in brick, block, or the foundation
• Doors and windows start sticking at the same time
• Floors are sloping or walls are bulging

A structural engineer gives an unbiased opinion because they do not sell repairs. Foundation repair companies can also inspect, but they may recommend their own services.

The bottom line

Most wall cracks are thin, straight, and caused by normal settling or seasonal changes. Patch those and move on. But wide, diagonal, stair-step, or horizontal cracks, or cracks that keep growing, can signal foundation or water problems. Measure and track any crack you are unsure about, and call a structural engineer if it gets bigger or comes with sticking doors and sloping floors.