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Foundation Cracks: What Is Normal and When to Worry

Learn about how foundation cracks can affect your home and how to evaluate any significant issues in your foundation.

Cracks and chips on the ruined foundation of the old building structure Adobe

Foundations are essential to every building structure. They serve to distribute the vertical load of building materials, occupants, and belongings to the soil. Foundations also keep the soil around and under the building from pushing it out of position. Therefore, when you discover an issue with the foundation, there is a need for considerable concern.

Since foundation problems are among the most expensive issues to repair, it is crucial to determine their severity. While some foundation problems are simple cosmetic problems, others require professional attention. This article will identify the types of foundation problems and recommend troubleshooting steps to help assess the issues.

Foundation Types and Materials

Several types of foundations can have unique problems. Knowing your foundation type and materials is helpful to make the most educated assessment when evaluating foundation problems.

Basement

A basement is often defined as an area mostly below ground and has a ceiling height of at least 7 feet. The basement floor is usually a nonstructural slab of concrete, although a basement may have soil as the floor.

Common basement foundation wall materials use poured concrete and concrete blocks in newer houses. Common basement foundation wall materials in older homes are bricks and stones.

Crawl Space

A crawl space is an area below the living areas with a ceiling height of less than 7 feet. The crawl space floor is usually soil. Crawl space foundation wall materials are concrete blocks and bricks.

Concrete Slab-on-Grade

A slab-on-grade foundation is built by removing the topsoil, leveling the soil, and pouring concrete on top.

The concrete may be a thick slab of uniform depth (a mat slab). The entire mat slab is effectively a footing. Mat slabs are used only in warm climates where the frost line is near the surface.

In cold climates, footings are dug around the perimeter of the building to below the frost line. Then, a thin, nonstructural slab of concrete is poured over the rest of the foundation (a monolithic slab).

Concrete Slab-on-Stem Wall

A slab-on-stem wall foundation is built by digging footings around the perimeter of the building to below the frost line. Walls are built on the footings to a point where the foundation is level and high enough to allow water to drain away from the foundation. The area inside the walls is backfilled, and a thin slab of concrete is poured on top.

The concrete may be thicker at load-bearing points inside the walls, but aside from these points, the rest of the slab is not considered a structural load-bearing element. Note that garage floors in basement foundations are often concrete slabs-on-stem walls.

Indicators of Foundation Problems

Here are some indicators to look for that may indicate a foundation problem. Note that these symptoms can have other causes, too.

  • Windows and doors that once operated properly now stick, rub, or do not open or close properly.
  • Floors that were once level are now noticeably out of level.
  • Tip: You can test if your floor is level by placing a marble on it. If it rolls, the floor is out of level.
  • Cracks appear at the corners of door frames and window frames, especially if the cracks are wider at the top.
  • Gaps appear between the base molding and the floor covering, especially if the gaps are wider at some points.

What Are Foundation Cracks?

Foundation cracks are one of the most common foundation problems. Bad soil, or soil that is too wet around the foundation, can cause the foundation to crack and lead to other foundation problems such as:

  • Settlement: Downward movement of the foundation
  • Uplift: Upward movement of the foundation
  • Rotation: Movement of foundation walls either inward or outward
  • Bulging: Part of the foundation wall protrudes outward from the rest of the wall.

Cracks that occur with other foundation problems may indicate a structural problem. A qualified professional, such as a structural engineer, should evaluate these cracks to determine the causes and appropriate repairs.

What Are Concrete Slab Cracks?

Concrete slabs may not crack if proper construction procedures are followed to near perfection. However, if any steps aren’t followed correctly, slab cracks can occur. Because many slab cracks are cosmetic, the cost often exceeds the benefit; thus, it is common and reasonable to see minor cracks in residential concrete slabs.

Hairline Cracks

Most cracks in nonstructural concrete slabs are caused by failure to follow one or more of the proper procedures. For example, the concrete finishers may add too much water to the concrete mix to make it more malleable. They may also need to rehydrate concrete after exposure to prolonged heat. When this water evaporates, the concrete fractures and shrinks in volume. These cracks are called hairline cracks (or shrinkage cracks).

Hairline cracks are cracks in a nonstructural slab that:

  • Remain about one-eighth-inch wide
  • Present no vertical displacement (one side of the crack is higher than the other)
  • Does not admit water
  • Doesn’t increase in size

You usually do not need to be concerned about cracks in concrete slabs that satisfy all of these conditions.

How to Evaluate Major Concrete Slab Cracks

When evaluating cracks in concrete slabs that do not qualify as hairline/shrinkage cracks, you will need to take extra steps to assess the situation. Use these four questions to help guide you through the process.

Where Is the Crack?

Areas intended for vinyl, tile, or wood/laminate floor coverings might adversely affect cosmetic and functional performance. Cracks with vertical displacement can cause cracks in tile and grout and squeaks in wood/laminate floor coverings.

How Big Is the Crack, Both Vertically and Horizontally?

Size matters when evaluating concrete cracks. The National Association of Home Builders (NAHB) standard for cracks in interior slabs requires repairing cracks that exceed three-sixteenths inches wide or high (vertical displacement). State regulators may have different standards.

Although smaller cracks may be patched, the patch may be more noticeable than the original crack. In addition, the patching material may crack or become dislodged.

Cracks with vertical displacement in driveways, walkways, and patios can create a trip hazard. Displacement of one-quarter-inch or more can present a trip hazard. Extra care should be taken if children or those with reduced mobility regularly use concrete slabs with greater than one-quarter-inch vertical displacement.

Is the Crack Admitting Water?

Water can damage materials used to build a house, causing the growth of fungus (or mold). Any crack that admits water is a cause for concern. These issues indicate a water problem that needs to be addressed to avoid damage to the structure.

The source of the water should be identified and eliminated as part of any crack repair. Do not simply seal the crack. Sealing a crack without dealing with the water sources can create more significant foundation problems.

Is the Crack Active?

Evaluating continuing activity is a matter of judgment and experience. Evidence of ongoing crack activity can greatly impact how best to deal with the problem. For example, when a crack appears where prior repairs have been attempted, it can signify continuing activity. It can also be a sign of a poor repair job or the normal aging of the repair material.

Crack monitoring devices exist, but they often are not practical on slab cracks, and they usually require monitoring over a long period.

How to Evaluate Foundation Wall Cracks

Evaluating a foundation wall crack is similar to evaluating concrete slab cracks. Use these six questions in your evaluation of foundation wall cracks.

What Foundation Material Is Cracking?

Evaluating a crack in a concrete foundation wall is often different from assessing a crack in a concrete block or brick foundation wall. For example, a stair-step crack only in the mortar between concrete blocks or bricks may be less of a concern than a crack that runs through the concrete blocks or bricks. It usually takes more force to crack blocks and bricks than crack mortar.

Where Is the Crack?

Crack location and direction are essential. For example, a crack in the upper area of the foundation wall may be nothing more than damage when the foundation was backfilled. A long horizontal crack near the middle of the wall (vertically) may indicate pressure on the wall from the soil. A long diagonal crack may indicate foundation settlement or uplift, especially if the crack is wider on one end.

How Big Is the Crack, Both Vertically and Horizontally?

The NAHB standard for cracks in foundation walls requires repairing cracks that exceed one-quarter-inch wide. State regulators may have different standards. Crack repair may be patching, according to the NAHB, although the proper crack repair depends on the cause of the crack.

Is the Crack an Indication of Other Foundation Problems?

Cracks sometimes occur as a result of other foundation problems. A crack associated with other foundation problems may be more of a concern, regardless of the crack size, location, and direction. Therefore, it is essential to look at the entire foundation wall, not just the crack.

Is the Crack Admitting Water?

Any crack that admits water is a concern for the same reasons as wet cracks in concrete slabs. The water sources should be identified and corrected before dealing with the crack.

Is the Crack Active?

Foundation wall crack activity is difficult to determine for the same reasons as concrete slab crack activity. There are ways to evaluate crack activity, but you should usually leave this to professionals who have the equipment and experience required to determine the crack activity and causes accurately.

Avoiding Foundation Problems

The best way to deal with foundation problems is to avoid them. The following suggestions can help you avoid the vast majority of foundation problems and can help keep your basement and crawl space dry.

  • Slope the soil away from the foundation at least 6 inches in the first 10 feet from the foundation. This method helps keep the soil near the house dry. Hard surfaces, such as driveways and porches, should slope away from the foundation at least one-quarter-inch per foot.
  • Keep gutters and downspouts clear and in good condition. Slope the gutters toward the downspouts. Use splash blocks or downspout extensions to discharge water at least 5 feet from the foundation.
  • Install and maintain irrigation systems to not discharge water near the foundation.
  • Install foundation plants that will remain at least 1 foot (preferably 2 feet) from the house when the plant is fully grown. This will help keep irrigation water away from the foundation and help prevent damage to the house wall coverings.
  • Install trees so that the branches will not hang over the house when the tree is fully grown. While uncommon, tree roots can damage the foundation. Tree branches can damage the roof covering.
  • Installing good soil under and around the foundation can reduce foundation problems when the house is built. Good soil means properly compacted soil with good load-bearing capacity. The ideal soil also lets water drain through if it gets wet. Coarse sand, gravel, stable clay, and mixtures of these are examples of good soil. Avoid soil that is high in organic materials or made with unstable clay.

Our Conclusion

Evaluating foundation problems can be challenging, even for professionals who see them every day. While some cracks can be ignored, others will require more time and money to resolve the issue. This article provides some general guidelines, but it does not substitute for professional training and experience.

If you are concerned about a foundation problem, we recommend calling a professional, such as a structural engineer. Foundation problems can worsen, so it is often easier and less expensive to repair them sooner rather than later.

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