Dan Bowers @ Holmes Inspection Company
Cracks in the walls are not restricted to homes owned by the Addams Family or Dr. Frankenstein. Cracks are found in most homes, but you=ll be glad to know that in most cases, they are not related to structural problems.
Approximately 80% of the cracks we see in residential structures are horizontal, vertical or diagonal. A large number are minor and do not require repairs outside of some basic caulk and repainting.
The following will help you better understand which cracks are potential problems and which are not: Horizontal Cracks: Horizontal cracks are usually structurally related. However, their significance depends on whether there is lateral movement and, if so, how much.
If a wall has moved one-third of its thickness out of plumb, it is in imminent danger of falling. If it has not moved, or if the movement is less than one-third of its thickness, the wall can probably be reinforced.
Vertical Cracks: Vertical or nearly vertical cracks are only structurally related when there is lateral movement (e.g., bow or shear). This assumes the crack is a consistent width from top to bottom.
In most cases, vertical cracks are hairline or slightly wider and are caused by normal shrinkage or contraction. Expansion and contraction are normal bor building materials. The more rigid the material is, the more likely it is that a crack will develop. Porous or less dense materials will be flexible and less likely to crack.
Vertical cracks in a wall with a bow or sheared wall planes are structurally related. Contraction cracks are hardly ever a structural concern.
Diagonal Cracks: Diagonal wall cracks that break through the building material are almost always structurally related. Step cracks in a block wall that only crack at the mortar joints and not through the block wall are not typically a structural problem, unless lateral movement is present.
When the bearing or foundation under a wall is not adequate, the wall will settle or sink at the weak area. The adjacent wall structures that are adequately supported will resist this movement. This situation will typically cause diagonal cracking.
To determine the cause or locate the source of a diagonal crack, draw a line perpendicular to the crack down from the approximate center of the crack. Once you locate and understand the source of the crack, proper corrections will be relatively easy to determine and address.
Cracks in Plaster Ceilings: There are generally 2 reasons why cracks in plaster ceilings occur:
1) Over the years, gravity will cause the plaster to crack. Typically, cracks develop in larger ceilings, in the direction of the longer dimension, at approximately 30 to 40 years. Cracks develop perpendicular to the first cracks at approximately 40 to 60 years. The ceiling loosens at approximately 70 to 90 years. Repair or replacement is then necessary.
2) When the frame structure above a ceiling is not stiff enough to keep the plaster from cracking, premature cracks are inevitable.
Excessive weight or bouncing can cause floors to flex and cause plaster on the ceiling below to crack.
There are various solutions to these problems. These solutions are influenced by such things as thickness, height and span of the wall; source of the problem; and available space.
If there is a structural problem with any of the cracks as explained above, it is highly recommended that you consult a professional engineer.