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- 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.
- If 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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