Most foundation cracks aren’t an emergency. Thin, vertical hairline cracks are often just concrete shrinking as it cures. You should only start to be concerned when a crack is wider than about a quarter inch, runs horizontally, forms a stair-step pattern or splits through the bricks themselves, keeps getting wider, or shows up along with sticking doors and sloping floors.
In this guide, we’ll help you tell the difference. We’ll cover the types of cracks, what causes them here in North Carolina, what you can check yourself and when it’s time to have a pro take a look.
Why Foundations Crack in the First Place
Almost every home develops a few small cracks over time. Concrete shrinks slightly as it dries, and houses settle a bit in their first few years. Those minor cracks usually aren’t a structural problem.
Bigger cracks usually point to movement in the soil under or around the foundation. Here are the most common causes we see:
- Clay soil that swells and shrinks. According to the North Carolina Geological Survey, expansive clay soils can occur almost anywhere in the state. These soils swell when wet and shrink as they dry, and even a small amount of movement can damage a foundation.
- Poor drainage. Gutters that overflow, short downspouts and ground that slopes toward the house all send water to the foundation.
- Settlement. When one part of the house sinks more than another, the foundation can crack. This is called differential settlement.
- Soil pressure. Wet, heavy soil can push sideways against foundation walls.
Types of Foundation Cracks and What They Mean
The direction and shape of a crack tell you a lot. Here’s how to read the most common types.
Hairline vertical cracks: usually minor
These are thin cracks that run straight up and down or close to it. In poured concrete, they’re often caused by normal shrinkage. If a vertical crack stays thin and doesn’t change, it’s usually not a structural concern. It’s still worth sealing if water gets through it.
Diagonal cracks: keep an eye on them
Diagonal cracks run at an angle, often starting at the corner of a window, door or wall. They can mean one part of the foundation has settled more than another. A crack that’s wider at one end than the other is a sign of uneven movement and should be checked.
Stair-step cracks: a sign of movement
Many North Carolina homes sit on brick or concrete block foundation walls, especially homes with crawl spaces. In these walls, cracks often follow the mortar joints in a zigzag pattern that looks like a set of stairs. Stair-step cracks usually mean part of the foundation is settling or shifting. They should be looked at by a professional, especially if they’re getting wider.
Cracks that run through the bricks: a red flag
Mortar, the material between bricks and blocks, is meant to be weaker than the brick itself. That way, when a wall moves a little, the mortar cracks first and the bricks stay whole. That’s why most movement cracks follow the mortar lines.
When a crack splits right through the bricks instead, it means the wall is under enough stress to break the brick. That’s a more worrying sign than a crack that only follows the mortar. If you see a crack cutting through several bricks, especially one that’s wide or still growing, have it checked by a professional soon.
Horizontal cracks: the most serious
A crack that runs sideways along a wall is often caused by soil pushing against it from the outside. If the wall is also leaning or bowing inward, the problem can get worse over time. Horizontal cracks deserve a professional evaluation as soon as possible.
How Wide Is Too Wide? The Quarter-Inch Rule
Width is one of the easiest ways to judge a crack. A good rule of thumb: if a crack is wider than about a quarter inch (6 mm), it’s time to have a professional look at it. That’s roughly the thickness of a pencil.
Hairline cracks thinner than a credit card are usually cosmetic, as long as they aren’t growing. Cracks between those sizes are worth measuring and watching. Keep in mind that width isn’t the only test. A narrow crack can still be serious if it’s horizontal, runs through bricks or keeps getting wider.
Warning Signs That Go Along With Cracks
A crack by itself doesn’t tell the whole story. These other signs can show that the foundation is actually moving:
- Doors and windows that suddenly stick or won’t latch.
- Floors that slope, sag or feel bouncy.
- Cracks in drywall, especially above doorways and at the corners of windows.
- Gaps between walls and the ceiling, or trim pulling away from walls.
- Cracks in brick on the outside of the house.
- Water coming into the crawl space or basement through a crack.
If you’re seeing several of these at once, it’s a stronger sign that something structural is going on.
What You Can Check Yourself
A little careful observation goes a long way. Here are a few safe ways to keep track of a crack.
- Measure it. Use a ruler or tape measure to check how wide the crack is at its widest point. If it’s wider than about a quarter inch, call a pro.
- Mark the ends. Put a small pencil mark at each end of the crack and write the date next to it. If the crack grows past your marks, it’s still moving.
- Take photos. Photograph the crack with a ruler beside it every few months. This gives you a clear record to compare.
- Check after heavy rain or a dry spell. Cracks that open and close with the weather often point to soil movement.
- Walk the outside. Look for water pooling near the foundation, clogged gutters and downspouts that empty right next to the house.
If the crack is in a crawl space, take care going in. Watch for sharp objects, wiring and pests. Wear gloves and a mask, and let someone know you’re down there.
When to Call a Pro
We recommend having your foundation checked if you notice any of the following:
- Any crack wider than about a quarter inch.
- A horizontal crack, or a wall that looks like it’s leaning or bowing.
- Stair-step cracks in brick or block, or cracks that split through the bricks themselves.
- A crack that’s getting longer or wider.
- A crack that’s wider at one end than the other.
- Cracks along with sticking doors, sloping floors or drywall cracks.
- Water coming through a crack.
Foundation problems usually get worse slowly, not suddenly. That’s good news, because catching them early often means a simpler repair. Waiting can let the damage spread to the floors, walls and framing above.
How We Fix Foundation Cracks
At Walsh, every repair starts with an inspection. We look at the cracks, check the floors for level and look for the cause, whether it’s water, soil or settlement. Then we explain what we found and recommend a fix that fits your home. You can learn more on our foundation repair page.
Sealing minor cracks
Small, stable cracks often just need to be sealed. This keeps water and moisture from getting into the crawl space or basement.
Stabilizing a foundation that’s moving
If part of the foundation is settling, it needs more support. That can mean installing piers, which are supports that reach down to firmer soil and carry the weight of the house. Our foundation repair guide walks through these options in more detail.
Fixing the water problem
Water is behind many foundation problems. Fixing gutters, downspouts, grading and drainage helps keep the soil around your home more stable. It also helps protect the repair itself.
Repairing the damage above
Foundation movement often shows up inside the house as sagging or uneven floors. If that’s happening in your home, our post on sagging floors over a crawl space explains the signs and how we fix them.
Frequently Asked Questions
Are hairline cracks in a foundation normal?
Yes, thin hairline cracks are common, especially in poured concrete. They’re often caused by normal shrinkage. Keep an eye on them, and call a pro if they start to widen or let water in.
Are horizontal cracks worse than vertical cracks?
In most cases, yes. Horizontal cracks are often caused by soil pressing against the wall from outside. Vertical hairline cracks are usually less serious.
How wide does a foundation crack have to be to worry?
A common rule of thumb is about a quarter inch. Cracks wider than that should be checked by a professional. Thinner cracks can still be a concern if they’re horizontal, run through bricks or keep growing.
Can I just fill a foundation crack with caulk?
Sealing a small, stable crack can help keep water out. But filling a crack doesn’t stop the foundation from moving. If the crack is caused by settlement or soil pressure, it will likely come back.
Do foundation cracks get worse over time?
Some stay the same for years. Others grow as the soil keeps moving with wet and dry seasons. Marking and photographing a crack is the easiest way to know which kind you have.
Get Your Foundation Checked
If you’ve found a crack and you’re not sure whether to worry, we can help. Walsh Crawl Space and Structural Repair inspects homes throughout the Charlotte, Greensboro and Winston-Salem areas. We’ll tell you what the crack means and walk you through your options. Schedule your free inspection today, or call us at (704) 302-7715.
