Why is my basement wall cracked?

basement foundation crack Morguefile x400
Basement foundation cracks can be serious, or just an annoyance, depending on the direction of the crack and the angle of displacement. Source: Morguefile

A homeowner’s nightmare: You walk into the basement on a cold dreary night… only to discover a crack in your basement wall! Before you panic and think your entire house needs to be reconstructed, there are a few things you need to know about basement wall cracks.  Basement walls crack for several reasons, and some are more severe than others.

  1. Horizontal cracks are the most severe and are found parallel to the ground. They are caused by lateral pressure from the surrounding soil and can cause the basement wall to bow out.
  2. Diagonal cracks that run from the top of the basement diagonally to the floor are normally caused by soil pressure. Other types of diagonally cracks that start anywhere in the wall or from a window or door corner can be caused by foundation settling and concrete shrinkage as it dries during construction.
  3. Vertical cracks run up and down. Shrinkage of materials, wall movement, or tipping walls can cause vertical cracks. They become a problem when combined with other cracks or when horizontal or shear movement occurs.
  4. Foundation floor cracks are usually caused by shrinkage of cement and often don’t pose a threat. Floor cracks to be concerned with are ones that cause displacement at the cracks or align with wall cracks. These may indicate water pressure from a damaged sump pump or drain tile.
  5. Step cracks are similar to diagonal cracks but occur in concrete block basement walls.

Most cracks occur gradually and may go unnoticed for many years until a leak is discovered. Most basement wall cracks can change seasonally, depending on where you live. Water is the threat to the foundation. Seasonal variations can cause basement walls to crack. If the soil is an expanding clay, the wall cracks may not be permanent but change as the water content in the soil changes at different times of the year. For example, in the spring when snow melts and the soil becomes saturated the wall may bow out slightly and crack. Come late summer when moisture has been drawn out by plants and evaporation, the crack may close. The same goes for winter and freezing soil. Ice can cause a similar movement and cracking as ice builds up and melts.

Two permanent issues caused by seasonal variation are:

  • When the soil settles and remains displaced
  • Sudden adverse climatic conditions such as snowmelt or rain and changing temperatures can cause rapid cracks in basement walls

Differentiating between a minor and a major crack can be difficult. If you are ever concerned about a crack developing in your basement wall, it is best to consult an expert. Structural engineers can review your basement walls to assess the magnitude of your crack. The engineer should have extensive knowledge of residential structures. They will be able to determine a cause and repair for the specific issue in your basement wall.

Before calling an engineer you may want to assess the wall yourself. The simplest way to do this is to measure the displacement. Using a 4-foot or longer level, laser level or plumb bob measure over the height of the wall and compare it to the corner measurements. Corners typically do not move due to being woven into a joint that resists any kind of movement.

Repairing basement walls can be simple fix.  Determining whether they are structural or non-structural will help to assess your fix. Types of repairs are:

  1. Patching using a polyurethane injection or hydraulic cement that expands forcefully to seal leaking cracks for non-structural cracks. Vertical and diagonal cracks can usually be repaired with a patch.
  2. Repair beams can be installed tight to the wall and are attached to the floor framing and concrete floor to add additional support to the wall. Excavation and straightening may be necessary if the displacement is serious.
  3. Rods and concrete reinforce block walls. Rods are placed within the hollow center of the block and cemented with concrete. It may be difficult to control how the rods are placed and cannot be installed into the top block.

A structural engineer can help evaluate how to fix the crack when using a repair beam or rods and concrete approach. It is always best to consult a professional contractor to do structural repairs.

Whether you’re building a new home or if you’re a long time home owner, there are several questions you may need to ask yourself about your basement foundation.

  • How do I know if I need a foundation repair?
  • Can I prevent a water issue?
  • Do I live in an area where expanding soils occur?
  • Does the climate vary significantly from season to season?
  • Should I install drain tiles to help deal with excess water around my basement?
  • What is the capacity of my sump pump?
  • What type of crack am I dealing with?

These questions can help you and your contractor determine if basement cracks may occur and the best ways to prevent them. It may be that you need extra reinforcement or to be sure to monitor your walls often to ensure a minor crack doesn’t become a major one.

Answered by Christina Hebb, Duraroot

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7 thoughts on “Why is my basement wall cracked?

  1. Don’t forget to divert outside water away from the foundation. Cracks or no cracks, basements will get damp if water collects near the outside wall.

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