Foundation Crack Identification: How to Know What’s Normal and What’s Not
Learn how to identify foundation cracks, when to worry, and what horizontal, diagonal, or stair-step cracks mean for your home. Protect your foundation with expert insight from Quality Waterproofing.
Every Crack Tells a Story — Here’s How to Read Yours
You walk into your basement and notice a crack running along the wall or floor. Your first thought? “Is my house settling—or do I have a serious foundation problem?”
Quality Waterproofing understands how unsettling that moment can be. Since 1955, we’ve helped St. Louis homeowners identify, repair, and prevent foundation damage. Cracks don’t always mean your home is in danger—but knowing which ones to worry about can save you thousands in future repairs.
This guide will help you understand the most common types of foundation cracks, what they mean, and when it’s time to call an expert.
Why Foundation Cracks Happen
Concrete and masonry are strong, but they’re not immune to the forces around them. Cracks can appear for several reasons:
Soil Movement: Expanding and contracting clay soils (common in the St. Louis area) put constant pressure on foundation walls.
Water Damage: Poor drainage and hydrostatic pressure push water into the foundation.
Temperature Changes: The freeze/thaw cycle causes concrete to expand and contract, leading to cracks.
Settling: Homes naturally shift slightly over time, especially in the first few years after construction.
The University of Missouri Extension notes that soil movement and moisture changes are leading causes of foundation stress in Midwestern homes.
Cracks in Concrete Foundations
Hairline cracks in concrete are common, especially in newer homes. These small, vertical cracks often occur as the concrete cures and shrinks slightly.
✅ Usually not a concern if:
The crack is narrow (less than 1/8 inch wide).
It runs vertically or diagonally in a straight line.
There’s no sign of moisture or movement.
🚫 A potential concern if:
Cracks are wider at one end than the other.
You see moisture, efflorescence (white residue), or mold near the crack.
The crack is expanding over time.
Even small cracks can allow water intrusion over time. Sealing early can prevent bigger problems later.
👉 Learn about our Foundation Crack Repair Services.
Foundation Cracks and Settling
Some settling is normal as a home ages—but excessive or uneven settling can cause serious damage.
Normal Settling Cracks:
Thin, vertical cracks in walls or near windows and doors.
Usually occur within the first few years of construction.
Problematic Settling Cracks:
Diagonal or stair-step cracks in brick or block foundations.
Cracks that widen over time.
Gaps where walls meet ceilings or floors.
Settling cracks can also signal differential settlement, when one part of the foundation sinks more than another. This can lead to uneven floors, sticking doors, and misaligned windows.
👉 Our Foundation Repair Services address the root cause—not just the symptom.
Foundation Cracks: When to Worry
Not every crack is an emergency, but some require immediate attention.
Call a professional if you notice:
Cracks wider than 1/4 inch.
Cracks that leak or show signs of water damage.
Horizontal or stair-step cracks (signs of wall movement).
Bulging, bowing, or inward-leaning foundation walls.
New cracks appearing suddenly after heavy rain.
The American Society of Home Inspectors (ASHI) recommends professional evaluation for cracks wider than 1/4 inch or those showing active movement (ASHI.org).
Horizontal Foundation Cracks — The Ones You Can’t Ignore
Of all crack types, horizontal cracks are the most concerning.
They usually appear in basement or crawl space walls made of concrete block or poured concrete and indicate lateral pressure—the soil is pushing against your wall.
Over time, this pressure can cause:
Inward bowing of walls
Structural weakening
Water intrusion
Potential collapse if ignored
At Quality Waterproofing, we often repair horizontal cracks with carbon fiber reinforcement or wall bracing systems to restore strength and prevent further movement.
👉 Learn about our Bowed & Buckling Wall Repair
Identifying Different Types of Foundation Cracks
Not all foundation cracks are created equal. Each type of crack tells you something different about what’s happening below the surface. Here’s how to tell them apart and what they might mean for your home:
1. Vertical Cracks
Usually run straight up and down.
Commonly caused by normal settling or concrete curing.
Typically not a structural concern but should still be sealed to prevent leaks.
2. Diagonal Cracks
Appear at an angle, often starting from corners of windows or doors.
Usually a sign of uneven settling or soil shifting beneath your foundation.
If the crack widens on one end, have it evaluated by a professional.
3. Horizontal Cracks
Run sideways along basement or crawl space walls.
Caused by outward soil pressure, frost heave, or hydrostatic pressure.
These are serious and should be inspected immediately—horizontal cracks often indicate structural stress.
4. Stair-Step Cracks
Follow the mortar joints in concrete block walls.
Suggest lateral pressure or foundation shifting.
May also signal water intrusion or poor drainage around the foundation.
5. Hairline Cracks
Very thin surface cracks that appear as concrete cures.
Usually cosmetic, but monitor them for changes or moisture over time.
If you’re unsure which type of crack you have, or if you see new cracks forming after heavy rain, it’s best to schedule a professional inspection before the issue worsens.
Preventing Foundation Cracks
Foundation cracks often start as water management problems. Here’s how to reduce your risk:
Direct Water Away from Your Home – Keep gutters and downspouts clean and extended.
Maintain Proper Grading – Ensure the ground slopes away from the foundation.
Seal Driveways & Sidewalks – Prevent water from seeping through expansion joints.
Control Indoor Humidity – Use dehumidifiers in basements and crawl spaces.
Inspect Annually – Catch small cracks early before they grow.
👉 See our guide on How to Keep Water Away from Your Foundation.
Professional Crack Evaluation
If you’re not sure what kind of crack you’re seeing, professional evaluation is the safest approach. During a free foundation inspection, our experts will:
Identify the crack type and cause.
Measure movement or displacement.
Recommend the best repair method.
Provide an honest, transparent estimate.
We don’t believe in scare tactics—just clear answers and proven solutions.
FAQs About Foundation Crack Identification
Q: Are small cracks in my foundation normal?
Yes, hairline cracks are common, especially in new homes. Monitor them for changes or leaks.
Q: Should I fill cracks myself?
DIY fillers can hide symptoms without fixing the cause. Professional repair ensures lasting protection.
Q: How much does foundation crack repair cost?
Costs vary depending on severity and repair method, but early fixes are always more affordable.
Don’t Ignore the Signs — Get Peace of Mind
Every foundation crack tells a story—but only a professional can tell you what yours means. For more info details, download our Foundation Crack Guide.
At Quality Waterproofing, we help homeowners turn worry into confidence. With decades of experience and proven repair methods, we’ll make sure your home stands strong for years to come.
