Know Your Foundation Type
Your house sits on one of three main foundation types. A slab is a single thick layer of concrete poured directly on the ground. A crawlspace lifts your home off the dirt, leaving a shallow empty area underneath. A basement is just a deep crawlspace you can stand up in. No matter which type you have, its job is to carry the weight of your house and keep moisture out.
Which Cracks Are Normal?
Concrete shrinks as it cures. It also expands and contracts with changing temperatures. Because of this, almost all concrete cracks eventually. Most cracks are harmless.
Hairline cracks are thin lines that look like a pencil mark. Vertical cracks that run straight up and down are usually just shrinkage. If a crack is less than 1/8 inch wide and does not grow over time, you probably have nothing to worry about. You can patch these with epoxy to keep water out.
When to Worry About Cracks
Some cracks tell you the earth under your house is shifting. This puts dangerous stress on your structure.
- Horizontal cracks: A crack running sideways along a basement wall is bad news. It means the soil outside is pushing inward against the wall.
- Stair step cracks: Cracks in brick or cinderblock walls that look like a staircase mean your foundation is settling unevenly.
- Wide cracks: Any crack wider than a quarter inch needs professional attention.
- Growing cracks: If a crack gets longer or wider over a few months, your foundation is actively moving.
| Crack Type | Danger Level | What to Do |
|---|---|---|
| Vertical hairline | Low | Seal with epoxy and monitor. |
| L shaped corner crack | Low | Seal to keep water out. |
| Stair step in block | High | Call a structural engineer. |
| Horizontal crack | Very High | Requires urgent professional repair. |
Water is the Biggest Enemy
Water destroys more foundations than anything else. When soil gets wet, it swells and pushes against your walls. When it dries out, it shrinks and leaves your foundation unsupported. The goal is to keep the soil around your house perfectly damp, not too wet and not too dry.
Check the dirt right next to your house. It should slope down and away from your foundation. This is called grading. If the dirt slopes toward your house, water will pool against your walls. You also need clean gutters and long downspouts. Your downspouts should dump water at least six feet away from your home. For bigger yard water issues, read up on landscaping and drainage solutions.
Warning Signs Inside the House
You do not have to go into a dark crawlspace to find foundation trouble. Your house will give you hints upstairs. If your doors suddenly start sticking or will not latch, the frame might be shifting. Look for gaps around your window frames.
Uneven floors are another big clue. If a marble rolls across your kitchen floor on its own, your joists might be sagging. You might also see diagonal tears in your drywall, especially extending from the top corners of doors and windows. Before you spend time fixing paint and drywall, make sure the framing behind the wall is actually stable.
Basements and Crawlspaces
If you have a crawlspace, it should have a thick plastic sheet covering the dirt floor. This vapor barrier stops ground moisture from rotting your wooden floor joists. The space should also feel dry and smell clean. Musty smells mean you have a moisture problem.
Basements often rely on a pit in the floor and a motorized pump to stay dry. Make sure you test your sump pump every year. You can learn more about maintaining those in our plumbing guide. Basements are also prime spots for dangerous soil gases to enter your home. It is smart to test for environmental hazards like radon gas if you spend time down there.
Foundation Repair Costs
Fixing a foundation is rarely cheap. Simple crack sealing might only cost a few hundred dollars. Major structural fixes like underpinning can cost tens of thousands. Underpinning involves driving steel piers deep into the earth to lift and support a sinking house.
Here is a rough look at what different repairs might cost. Keep in mind that these are ballpark estimates. Prices vary a lot based on your region, the size of the job, and the age of your home.
