What do they mean?

Disclaimer: I am a home inspector with basic knowledge in this area. I am not a structural engineer, concrete, or masonry professional. The information in this article is the information I use when preforming a home inspection.

There are 3 basic types of foundation walls.

Poured concrete walls. This type of wall is the most common type of foundation wall you will see in current residential construction. The concrete is poured into a form. When dry the forms are removed.

Concrete masonry units. Other names are CMU’s, cinder blocks or concrete blocks. These are the rectangular blocks that are stacked on top of each other with mortar in between holding them together. This type is the second most common type of foundation wall.

The third type is constructed of brick, stone, or clay tiles. Most of these foundation walls are in older or historic homes.

Cracks in foundation walls can be caused by a few basic reasons. Pressure is pushing against the wall itself, called a lateral load. The soil or foundation under the wall is moving or shifting. Water, is the water in the soil getting to much or is it drying out? Or, is it just the drying process of the material used to build the wall?

Here are the most common types of cracks seen in a foundation wall.

Shrinkage cracks.
These cracks are very common with poured concrete walls. They are a thin, hairline crack that is shallow or just on the surface. They tend to happen within the first year of pouring. They are not straight, just normally meander. Shrinkage cracks are usually caused by the drying process of concrete. General concession is that these cracks are cosmetic in nature.

Vertical cracks.

These cracks go up and down the wall. Most of the time they are caused by foundation settlement, with most of them not considered structural issues.

When you have a vertical crack that is wider at the top than the bottom or wider at the bottom than the top, it is cause for concern due to the forces that are causing this. Most of the time when you see this it is due to differential settling. This requires evaluation by a structural engineer or masonry contractor.

Horizontal cracks.
These cracks are serious and need prompt attention. They are caused by either soil or water pressure against the foundation wall pushing in, also called lateral load. When you look at the wall it will be bowed inwards.

  • Some features that cause horizontal cracks.
  • Back filling before the concrete has cured.
  • Heavy equipment driving near the foundation wall.
  • Moisture or hydrostatic pressure in soil around the wall pressing against it.
  • Freeze thaw cycle.
  • Expansive soils.

Diagonal cracks.

Most diagonal cracks do not pose a serious threat. These cracks, as opposed to vertical cracks, run at about a 30-degree angle. The most common cause of diagonal cracks is concrete curing or settlement over time. What to do about them? Take a picture and measure the width of the crack. If the width is less than the width of a quarter, check back in 6 months to see if any change has happened. If you are considering covering the crack/wall, have evaluation for repair prior to covering.

Stair Step cracks.

These cracks are found in concrete block, brick, and stone walls. They occur along mortar joints. These cracks form due to foundation settlement or moisture issues outside the wall. Stair Step cracks are an indication of a serious issue and need evaluation promptly by a qualified individual.

If you see a crack in a foundation floor and it aligns with a crack in the wall. Get it evaluated by a qualified professional promptly. This is serious.

Those are the most common types of cracks you will see in a foundation wall. If you see any of these, take a picture and measure the width of the crack for a baseline. If you are new to an older property, ask about how long the cracks have been there, are they getting worse or have any repairs been done to them?

Lastly for your peace of mind, have any cracks in the foundation walls or slab you find evaluated by a qualified professional.