Structural

How can you be certain that a crack is structurally deficient?

• There are generally three types of cracks—vertical, horizontal and diagonal. However, this forum does not allow for every variation to be discussed. If you understand the three basic crack patterns outlined below, you will have a reasonable understanding of approximately 85% of all of the cracks that you will see. Let’s cover them one at a time.

Vertical Cracking

• Vertical cracking is not structurally related or deficient unless there is lateral movement, displacement, bowing, or if the crack is uneven from top to bottom. If the plane of the wall is the same on both sides of the crack, it is typically a contraction crack and not a structural issue.
• Since everything expands and contracts, it is common in commercial work to provide control joints in areas where expansion and contraction is expected. However, control joints are not typically installed in residential construction. Ridged materials, such as poured-in-place concrete, tend to crack from expansion and contraction much easier than more flexible materials.
• If all loads were evenly distributed on this type of wall, were a consistent thickness and were the same height for the entire length, the vertical cracks would most likely occur at or close to the center of the wall.
• If there is a window or door in the wall, the crack will occur at this opening, as a window or door creates a void or weakness in the wall. The crack would typically occur in the center of the wall if there were no such opening. The vertical cracking in this situation may be 5–10 degrees out of plumb (vertical), however, it is still considered a vertical crack. Such cracks are most common in poured-in-place concrete and concrete block construction.
• The rule of thumb is to expect vertical cracking if a wall made of ridged material is 32' or longer and forms a straight line without pilasters, jogs or other structures, such as a masonry chimney. First look in the center of the wall, unless there is a window. The crack will almost always occur at the window in this scenario.

Horizontal Cracking

• Horizontal cracking in block construction is structurally related because the bond between the block is broken, however, this does not mean that the wall will collapse. The amount of movement and the cause of movement are important issues to consider. Frost, backfilling, or a significant unbalanced load may cause cracking.
• While no cracking is desirable, it is important that you understand the differences. A frost line crack is not likely to have serious repercussions unless the conditions, such as negative grades, are not corrected.
• Cracking due to poor backfilling practices, or heavy equipment close to the walls, is usually a one-time occurrence.
• Movement caused by an excessive unbalanced load presents the most serious situation, and failure is progressive. A significant unbalanced load may be destined for collapse. Example: A 4' unbalanced load against an 8'' block wall is the current limit. It was not unusual to build homes with 8'' block and 6' or 7' of unbalanced load in the 1940s and 1950s in many areas of the country.
• The engineering community suggests a rule of thumb that if a wall has moved 1/3 of its thickness, then the wall is considered to be in imminent danger of collapse. This may also suggest that if there is only 1/2'' of movement, it is not likely that the wall will collapse.

Diagonal Cracking

• Diagonal cracking is almost always structurally related. Diagonal cracking is defined in this example as a crack that tears through the material, not a step crack that follows the mortar joints. To understand the source or cause of a diagonal crack, draw an imaginary line perpendicular to the center of the crack, down. This should point to the source or reason for the cracking.
• Example: Assume that a frame floor system is carrying enough weight to cause it to sag, and the subject wall is parallel to the joist system. The sag would typically be farthest from the bearing points (at mid-span), where there is likely to be diagonal cracking. Draw an imaginary line perpendicular to the crack, from the center of the crack, downwards toward the floor. This should point to mid-span of the floor joist.
• In the above example, the cracking would typically occur 1'–4' from the corner of the settled wall, because the wall that is perpendicular to the settled wall is likely to be supported differently and resist movement. A wall that is on a foundation, beam or is perpendicular to the floor joists, will be supported better than a wall that is parallel to the floor joists.
• you are looking at a foundation wall with diagonal cracking, you should be concerned, however, determining the source is fairly easy—again, draw an imaginary line perpendicular to the diagonal crack and follow to the floor. This does not mean straight down to the floor, or 90 degrees to the floor. It means that you follow the line on the angle that is perpendicular to the crack.
• Being able to determine the cause or the source of the cracking problem will be a guide to the action or solution needed. By understanding a number of different crack patterns and their significance, causes and sources, the solutions are relatively straightforward.
• If a design solution may be required, a structural engineer should be consulted for an opinion, options and an recommended solution.  Learn more about the structure of a home.

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