The short answer
Most foundation cracks aren't serious. Thin vertical cracks under 1/16 inch are usually just concrete shrinking. Cracks that are horizontal, stair-stepped, wider than 1/4 inch or with one side higher aren't normal, because they can mean the wall or the soil is moving. Those are worth having measured.
Key takeaways
- Hairline vertical cracks under 1/16 inch are usually normal.
- Horizontal cracks and offset cracks are the ones to take seriously.
- Date your cracks and measure them again every month.
- Cracks inside the house can point to the foundation too.
You found a crack in foundation concrete and now you can't stop seeing it. We get it. We've looked at thousands of them, and the good news is that most don't mean much. This guide will show you how we tell which is which.
Are foundation cracks normal?
Yes, most foundation cracks are normal, at least the thin ones. Concrete shrinks as it cures, and it isn't very good at stretching. So a new wall develops small cracks to relieve the stress, usually in the first year or two. A wall that's cracked isn't the same as a cracked foundation that's failing.
That's why nearly every house has at least one. A hairline crack in foundation concrete is usually cosmetic. What you want to know is what kind of crack you've got and whether it's changing.
People also find cracks in foundation walls during other projects, like when they pull down old paneling or move a water heater. Those can look alarming, because you don't know how long they've been there. Old cracks usually have dirt, paint or cobwebs inside them, and new ones have clean, sharp edges. That little detail can tell you a lot.
Types of foundation cracks (with pictures)
There are six types you'll usually see, and each has a different level of risk. We've rated them below, using the same way of thinking we use at your wall.
Hairline cracks
Thin as a pencil line, usually from shrinkage. Risk is low, so just mark them and watch.
Vertical foundation cracks
These run straight up and down, and vertical foundation cracks are the most common kind in poured walls. Risk is usually low, though they can leak.
Diagonal cracks
These run at an angle, often from a window corner or across a wall. They can mean one end of the wall has settled a little. Risk is moderate, so measure them.
Horizontal foundation cracks
These usually mean soil is pushing the wall inward. Horizontal foundation cracks carry the highest risk on this list, and they need a measurement soon.
Stair-step cracks
These follow the mortar joints in block or brick. They point to movement, usually settling at one corner. Risk runs moderate to high, depending on the width.
Cracks with one side higher
If you can feel a lip when you run your finger across it, the concrete has shifted. That's movement rather than shrinkage. Risk is high, so call someone.
Why does my foundation crack?
Your foundation cracks because concrete shrinks, soil moves or water pushes. If you're asking what causes foundation cracks at your house, here are the usual suspects:
- Expansive clay. It swells when wet and shrinks when dry, moving the foundation with it. The USGS has good background on expansive soils.
- Water. Poor drainage saturates the soil and adds pressure.
- Tree roots. Big trees pull moisture from clay near the foundation.
- Plumbing leaks. They can swell soil or wash it away.
- Poor compaction. Fill dirt that wasn't compacted settles over time.
How to tell if a crack is getting worse
You can tell a crack is getting worse by measuring it over time. It's simple, and all you need is a pencil, a ruler and a phone.
Mark each end of the crack with a pencil line, then date it. Measure the width and write that down too. Take a photo with the ruler in the frame, and do it again each month for six months. If you want more precision, a crack monitor from a hardware store costs little and shows tiny changes.
Clay soil moves with the seasons, so a crack may open in August and close again in March. That doesn't always mean trouble. A crack that keeps growing every season does.
Cracks inside the house that point to the foundation
Cracks inside your home can point to foundation movement, even when the foundation looks fine. Here's what we'd pay attention to:
- Drywall cracks running up from the corners of doors and windows
- Cracks where the ceiling meets the wall, especially with a gap
- Tile that's cracked in a straight line across the floor
- Doors that have started to stick or swing open
One small drywall crack is often just the framing drying out. Several of them in one part of the house, showing up together, tell a different story. Our guide on signs your house is settling goes through what to check.
Outside, look at the corners of the house and above windows, where brick shows movement before most other materials do.
When to call a pro
Call a pro when the crack shows signs of movement. Here's the short list:
- Any crack wider than 1/4 inch
- Any horizontal crack
- A crack with one side higher
- A crack that's growing, however thin
- A crack in foundation wall sections that's letting water through
- Several new cracks at once
You've got two good next steps. Learn about sealing a crack the right way, or book a free foundation inspection so someone can measure it. If you want a sense of pricing first, see foundation repair prices. And if the cracks turn out to be part of something bigger, foundation repair contractors can look at the whole picture, not just one line on one wall.
Foundation crack questions
How big of a crack is too big?
Anything wider than 1/4 inch deserves a professional look. So does any crack that's growing, however thin it is, and any crack where one side sits higher than the other. Width isn't everything, since a thin horizontal crack can matter more than a wider vertical one.
Do all houses have foundation cracks?
Nearly all of them do. Concrete shrinks as it cures, so most poured foundations get a few thin cracks in the first years. You may not see them behind drywall or paint. Having a crack isn't the issue. What matters is the type, and whether it's changing.
Can I fill foundation cracks myself?
Yes, if the crack is thin, dry and not moving. Hardware stores sell injection kits and sealants that work on those. Don't patch a crack that's wider than 1/4 inch, horizontal or offset, since that would hide the sign a pro needs to see.
Are horizontal cracks always serious?
They should be treated as serious until measured. Most mean soil is pressing on the wall, though some are just old and stable. A cold joint between concrete pours can also look like one. Measuring the wall's bow and tracking it for a few months tells you which you've got.
Do foundation cracks affect home value?
They can. Thin shrinkage cracks barely matter, but signs of movement can lower offers or scare off buyers. A written report and repair record goes a long way. Fixing a real problem before listing usually costs less than the discount a nervous buyer will ask for.
Why is my foundation cracking?
Usually, it's shrinkage, soil movement or water. Young concrete shrinks as it cures. Clay soil swells and contracts with the weather, and plumbing leaks or poor drainage can make that worse. The crack's shape usually tells you which one's at work.
What do normal foundation cracks look like?
Normal cracks tend to be thin, close to vertical and fairly straight, under about 1/16 inch wide. They don't leak much, and they look the same from one year to the next. If you can't fit a dime into it and it isn't changing, you can usually just keep an eye on it.
Are vertical foundation cracks normal?
Usually, yes. Most vertical cracks come from concrete shrinking and they rarely threaten the structure. They're still worth sealing if they leak. A vertical crack that's wider at the top or bottom, or that keeps growing, can point to settling and needs measuring.
Run into a term you don't know? This may help: foundation terms explained.