Cracks in Walls: Cosmetic or a Foundation Problem?

Most cracks in walls are cosmetic. A thin vertical crack, or a short one running up and away from the corner of a door or window, is usually the house drying out and shifting with the seasons, and paint and patch is a fair answer. The cracks that earn a closer look are different: wide enough to catch a fingernail, zigzagging or running on a steep diagonal, getting longer, or coming back in the same spot after you patch them. Even then, the crack by itself rarely decides anything. The pattern does. A crack plus a door that suddenly sticks plus a floor that has started to slope says far more than any single line in the drywall.

So before you call anyone, give the crack an afternoon of attention. Below is what causes wall cracks, a check you can run today, and how to sort what you find into “patch and watch” or “have the foundation looked at.”

Why walls crack in the first place

A house is never perfectly still. Most of the movement is small and harmless, and drywall and plaster are simply the first materials to show it.

Drying and shrinking. Framing lumber loses moisture for years after a house is built, and it shrinks as it dries. Drywall is hung in sheets with taped seams, and the weakest spots are the seams that meet at the corners of doors and windows, where the framing is interrupted. That is why so many cracks start at a corner and run up toward the ceiling.

Seasonal swings. Wood, drywall and plaster swell a little in humid months and shrink in dry ones. The National Association of Realtors, in a piece on when not to ignore wall cracks, puts most cracks down to materials expanding and contracting with moisture and temperature. That is the common explanation, and for a lot of cracks it is the right one. Where it falls short is the crack that keeps growing, or the one that arrives with other symptoms. Expansion and contraction do not explain a door that used to close and no longer does.

Settling. Settling is the house sinking slightly as the soil beneath it compacts, mostly in its first years. Even settling across the whole house is rarely a problem. Trouble starts when one part of the house sinks more than another, because the frame above has to bend to follow it.

Soil that moves. Some ground does not just compact; it swells and shrinks. Expansive clay soil swells when it gets wet and shrinks as it dries, so a house sitting on it can be pushed up in a wet spring and dropped again in a dry summer. The Colorado Geological Survey’s guide to swelling soils explains how that repeated push and pull cracks foundations, slabs and the walls above them. If you live where clay is common, a crack that opens in late summer and narrows after the rains is a clue worth writing down.

How to tell if a crack is structural: a check you can do today

You need a pencil, a phone camera, a credit card and a few minutes in each room. The point is to replace “it looks bad” with something you can measure.

• Mark the ends. Draw a short pencil line across each end of the crack and write today’s date beside it. If the crack grows, you will see it pass the line.
• Photograph it with a scale. Hold a credit card flat against the wall next to the widest point and take a clear photo. A hairline crack is one thinner than a card’s edge. Do this for every crack you find, so you have a dated record instead of a memory.
• Note the direction. Vertical, short diagonal from a corner, long diagonal, stair-stepped, or horizontal. Write it down next to each photo.
• Try the doors and windows. Open and close every door and window near the crack. Ones that rub, stick, swing open on their own, or no longer latch are telling you the opening has changed shape.
• Look at the edges of the room. Check for gaps between baseboards or trim and the wall, and for a gap where the wall meets the ceiling. Check whether tile near the crack has cracked too.
• Check the floor. Set a marble or a round pencil on the floor in a few places. One that rolls the same direction every time suggests a slope.
• Walk outside. Look at brick or block walls for a stair-step crack, which zigzags along the mortar joints like a staircase. Look for gaps around exterior door and window frames.
• Come back later. Recheck the pencil marks in a month, then again at the change of season. Most cosmetic cracks stay put. A crack that has moved past its marks is no longer a guess.

This is roughly how professionals think about it too. The Texas Real Estate Commission’s guidance for inspectors on foundation performance frames the job as judging how the whole house is behaving, not reading meaning into one crack. Doors, floors, walls and the exterior are read together.

Patch and watch, or have the foundation looked at

Once you have a week or two of notes, the crack usually sorts itself.

Patch and watch when you have a thin crack, vertical or a short diagonal from a corner, no companion signs, and pencil marks that have not moved. Tape it, mud it, paint it, and keep your dated photo. If the patch holds through a full year of seasons, you have your answer.

Have the foundation looked at when two or more signs show up together: a crack plus sticking doors, a gap at the ceiling plus a sloping floor, a stair-step crack outside plus a new crack inside. Also when a crack grows past its marks, or reopens in the same place after a careful patch. That reopening is the most useful thing a patch can tell you. It is not bad workmanship; it is movement.

A wall crack is the messenger. The cause, if there is one, lives below it. If your walk around the basement or the outside of the house turns up cracks in the concrete itself, our guide to foundation crack types and what each one means covers that side, so you can match what you see in the walls to what is happening underneath.

What a horizontal crack in a foundation wall means

One shape deserves its own warning. A horizontal crack in a foundation wall, usually in a basement or a block wall, is more serious than a vertical one. Vertical cracks often come from concrete shrinking as it cures. A horizontal crack more often means soil pressure from outside is pushing the wall inward, and a wall under that kind of load can begin to lean or bow.

If you find one, do not wait a season to see what happens. Lay a straightedge or a taut string along the wall to see whether it bulges, take a dated photo, and have it assessed soon. Our guide to bowing basement walls explains what that assessment looks for and the ways those walls are stabilized.

Who should assess it

A common worry is that a foundation company will look at a crack and find a reason to sell a repair. You have two ways to keep the assessment honest.

The first is a structural engineer, an engineer who assesses whether the house’s frame and foundation are sound, independent of any repair company. An engineer’s report tells you what is moving and why, and it gives you something to hand every contractor so you are comparing the same job.

The second is to ask each company you call who will actually assess the house and what they will put in writing. Ask for findings, not just a quote: what they measured, where, and what they think is causing it. Bring your dated photos and pencil marks. A month of notes from you is better evidence than a single visit from anyone.

Does insurance cover cracks in walls?

Usually not when the cause is settling, soil movement or slow wear, which standard policies tend to exclude. A sudden covered event, such as a burst pipe that soaks the soil, can be handled differently. Policies vary, so read your own exclusions before you file anything. We go through the details of whether homeowners insurance covers foundation repair in a separate guide.

If the signs add up

If your check turned up two or more of the signs above, the next step is an inspection, not a repair. Find foundation repair companies near you on our home page, filter to your city, and ask a few of them to come look.

Know that “crack repair” and “foundation repair” are often sold as separate jobs. Of the 2,076 foundation companies in our directory nationwide, 241 list foundation crack repair as a service, while 413 list foundation repair itself. A shop that patches cracks may not stabilize a foundation, so ask each one what they would do about the cause, not only the crack.

And ask about cost to look before anyone comes out. About 27% of the companies we list advertise free estimates, which means most do not say. Ask up front, get every finding in writing, and keep your own notes alongside theirs.