How to Check Foundation Cracks

Foundations crack. It’s just what concrete does. The question isn’t whether you have cracks—it’s whether those cracks are normal settling or signs of a serious problem. Most are cosmetic. Some are structural. Knowing the difference can save you from expensive repairs or give you time to address real issues.

Why This Matters

Your foundation supports everything above it. When something goes wrong down there, the effects show up everywhere—sticking doors, cracked drywall, sloped floors. The earlier you catch problems, the easier (and cheaper) they are to fix.

• Ignoring cracks – Small problems become big ones
• Panic over nothing – Many cracks are purely cosmetic
• Water entry – Even small cracks can let moisture in
• Structural movement – Can worsen over time if not addressed

Monitoring is free. Repairs are not.

Types of Cracks

Usually Fine (Monitor Only)

Hairline cracks – Less than 1/8 inch wide, vertical or nearly vertical. These often appear as concrete cures and settles in the first few years.

• Thin as a pencil line or smaller
• Run straight up and down
• Not getting wider over time
• No water seepage
• Same width from top to bottom

Most homes have a few of these. They’re not a problem.

Potentially Concerning

Diagonal cracks – Run at an angle, often from window or door corners. Can indicate differential settling where one part of the foundation sinks more than another.

Stair-step cracks – In block or brick foundations, cracks that follow mortar joints in a step pattern. May indicate wall movement.

Cracks wider at top or bottom – If the crack isn’t the same width all the way down, something is moving.

Seriously Concerning

Horizontal cracks – Often indicate pressure from soil or water pushing against the wall. This is a structural warning sign.

Wide cracks – Anything over ¼ inch deserves attention.

Growing cracks – If you can see the crack getting longer or wider, something is actively moving.

Water seeping through – Any active water entry needs to be addressed.

Displacement – If the wall on one side of the crack is pushed in or out relative to the other side.

How to Check

1. Walk the Interior

With your flashlight, walk along every interior foundation wall in your basement or crawlspace:

• Look for cracks of any size
• Note their location, direction, and approximate width
• Check for signs of water—stains, efflorescence, dampness
• Look for any bowing or bulging of walls

2. Check the Exterior

If possible, look at exposed foundation walls outside:

• Walk around the perimeter
• Note any cracks visible from outside
• Check grading—soil should slope away from foundation
• Look for areas where water pools near walls

3. Document Everything

For each crack you find:

• Take a photo with something for scale (ruler, coin)
• Write down the location
• Note the direction (vertical, horizontal, diagonal)
• Estimate the width
• Record the date

The Monitoring System

For cracks you’re unsure about, set up a simple monitoring system:

1. Mark the ends – Use a pencil or crayon to draw a line at each end of the crack
2. Date the marks – Write the date next to each line
3. Measure at reference points – Use a ruler to measure width at the widest point, write it down
4. Take photos – Capture the crack with your marks and measurements visible
5. Check monthly – See if the marks are still at the crack ends, measure again

If the crack extends past your marks or gets wider, something is moving.

You can also buy crack monitors—inexpensive plastic gauges that adhere across a crack and show any movement.

Warning Signs of Major Problems

Seek professional evaluation if you notice:

• Horizontal cracks of any size
• Cracks that are actively growing
• Doors and windows sticking throughout the house
• Floors that feel sloped or uneven
• Walls pulling away from ceiling or floor
• Significant water entry through cracks
• Bulging or bowing foundation walls

These can indicate serious structural issues that won’t resolve on their own.

DIY vs. Call a Pro

DIY: Monitoring existing cracks, documenting changes, managing surface water drainage.

Call a pro: Horizontal cracks, growing cracks, water intrusion, structural concerns, or if you’re just not sure. A structural engineer can give you an unbiased assessment—consultations typically cost a few hundred dollars and can save you from unnecessary work or alert you to serious problems. Find a contractor →

How Often to Check

• Initial assessment: Document all cracks when you move in
• Quick check: Every 6 months
• Full inspection: Once a year, including photos and measurements
• After major events: Earthquakes, extreme flooding, significant changes in soil moisture

The Bottom Line

Most foundation cracks are nothing to worry about. But the ones that are problems tend to get worse if ignored. Spend thirty minutes once a year documenting what you’ve got. If something changes, you’ll catch it early when solutions are simpler and cheaper.