Foundation cracks: which ones to worry about

Finding a crack in your foundation can be alarming, but most foundation cracks are not a structural problem. Concrete and masonry crack as they dry, age and move with the seasons. What matters is the shape of the crack, whether it is still moving, and whether the rest of the house shows signs of movement too.

This guide explains the common crack patterns, how to keep track of a crack yourself, and when it is time to bring in a structural engineer. For what repairs cost, see foundation crack and mortar repair and foundation settlement repair.

Why foundations crack at all

Fresh concrete is at its largest right after it is poured. As it dries, it shrinks, and when the surrounding structure holds it in place, it cracks. The National Ready Mixed Concrete Association puts it plainly: cracking "is not necessarily a sign of poor materials or workmanship or a structural problem with the concrete wall." [1]

Engineers who write foundation guidelines in Texas say the same thing from the other direction: the majority of cracks do not compromise structural integrity. [3] That is why many home reports list minor cracks as something to watch, not something to fix right away. See the minor foundation cracking finding for how it usually shows up.

Settlement is different. Settlement cracks come from uneven support under the footings, the concrete base the walls sit on, and sometimes from soils that swell and shrink. [1] These cracks can keep growing if the cause is not fixed.

Common crack patterns and what they usually mean

What you see	Usual cause	Level of concern
Thin vertical or slightly diagonal crack in poured concrete, often in the middle of a wall	Drying shrinkage	Usually low. Watch it. [1]
Crack that is wide at one end and narrows to a hairline at the other, often near corners or windows	Settlement	Watch closely. Have it looked at if it grows. [2]
Stair-step crack following the mortar joints in block or brick	Settlement, or expansion and contraction of the masonry	Depends on width and whether it grows. [4]
Crack whose two sides no longer line up, with one side pushed out or down	Differential settlement, where one part of the house moved more than another	Have it evaluated. [2]
Horizontal crack in a block or brick foundation wall, or a wall bowing inward	Soil pressure from the outside, often from backfill, water or freezing soil	Potentially serious. Call an engineer. [5]
Crack that opens in winter and closes in summer	Seasonal temperature and moisture movement	Usually low. Seal with a flexible sealant. [4]

A few details help you read a crack. In block foundations, shrinkage cracks often form during the building's first year and are "rarely serious." [2] A clean crack points to recent movement, while a dirty or previously filled crack may be inactive. [2] Age matters too: a half-inch crack in a new house can mean fast settlement, while the same width in a 50-year-old house may reflect very slow movement over decades. [2]

Signs that point to movement, not just a crack

A crack on its own tells you less than the house around it. These signs suggest the foundation may be moving [3]:

• Doors and windows that stick, or frames that are out of square
• Floors that slope enough to notice (engineers note that a slope over about 1 percent is usually noticeable)
• Gaps opening between walls and ceilings or floors
• Brick rows that are no longer level, or brick panels that lean or bulge
• Cracked or separated floor coverings

Any one of these can have other causes. When several show up together, or show up along with a growing crack, it is worth a closer look. The heaving or settling finding describes what that looks like on a report.

How to track a crack over time

You do not need special tools to learn whether a crack is moving. What you need is a record.

1. Mark the ends. Draw a short pencil line across each end of the crack and write the date next to it. If the crack grows past the line, you will see it.
2. Measure the width. Measure at the widest point with a ruler or a tape measure, and mark the spot so you measure in the same place each time.
3. Take photos. Hold a ruler or a coin next to the crack so the photos show scale. Take them from the same spot each time.
4. Check on a schedule. Look every few months and after heavy rain or a long dry spell. Some cracks open and close with the seasons, so it can take six months or more to see the full pattern. [2]
5. Consider a crack monitor. A crack monitor is a small plastic gauge that mounts across the crack. Its two plates slide past each other as the crack moves, so you can read how much it has changed. Even two strips of tape marked with pencil lines across the crack will show movement. [5]
6. Note any water. Write down if the crack leaks or shows damp stains or white powder after rain.

Engineers use the same idea on a larger scale: repeated floor level measurements over months or years show whether a foundation is still moving. [3]

What causes cracks to grow

Water is the most common driver. Gutters that overflow, short downspouts and soil that slopes toward the house all put more water against the foundation. In Texas and other areas with clay soils that swell when wet and shrink when dry, moisture swings can move a foundation. [3] Texas engineering guidelines recommend keeping soil moisture fairly even on all sides of the house, avoiding overwatering, extending downspouts well past the foundation, and sloping the ground away at least 6 inches in 10 feet. [3] Large trees and shrubs close to the house can also dry out the soil under it. [3]

For outside drainage fixes, see the exterior guides. Moisture under the house is covered in our crawl space basics article.

When to call a structural engineer

Call a licensed structural engineer when you see:

• A horizontal crack or a bowing or leaning wall (see bowing or leaning walls)
• A crack that keeps widening when you track it [1]
• A crack whose sides are offset, not just separated
• Cracks together with sticking doors, sloping floors or wall-to-ceiling gaps
• A crack wider at one end that keeps growing

An engineer looks at the whole house, finds the cause and recommends a repair. Engineering and contractor licensing rules vary by state. In Texas, for example, foundation guidelines call for the evaluation and repair design to be done by a professional engineer licensed in that state. [3] Your local building department can tell you whether a repair needs a permit.

What the repair usually involves

Thin, stable cracks are often just watched. If they let water in, they are sealed. Cracks that open and close with the seasons get a flexible sealant, while cracks that have stopped moving can be filled with mortar. [4] On brick and block foundations, crumbling mortar is scraped out and replaced, a job called repointing, and the new mortar should match the hardness of the old so it does not damage the surrounding masonry. [4] See deteriorated mortar on a foundation.

Settlement repairs depend on the cause and can include new piers, permanent supports in place of temporary posts, or bracing a wall. Those are covered on the foundation settlement repair page.

HomeCloud is a licensed general contractor that evaluates homes and prices and does the repairs. If you have a crack you are unsure about, we can look at it with the rest of the house and send you a priced estimate.

Sources

1. National Ready Mixed Concrete Association, CIP 7: Cracks in Residential Basement Walls
2. InterNACHI, Inspecting Foundation Walls and Piers
3. ASCE Texas Section, Guidelines for the Evaluation and Repair of Residential Foundations, Version 2
4. National Park Service, Common Problems with Brick Masonry
5. U.S. General Services Administration, Monitoring and Evaluating Cracks in Masonry