Cracked Foundation Wall

Cracks in foundation walls can be of no significance or a major structural defect, which can be expensive to correct. Proper evaluation is therefore very important to determine:
(1) If repair work is warranted and,
(2) Details for effective repairs.

As a licensed professional engineer, I am called in to evaluate cracked foundation walls frequently. Unfortunately, repairs for defective foundation walls can easily cost tens of thousands of dollars. However, much money can also be wasted based on incorrect evaluation by unqualified persons.

Water in the soil around a basement is often one of the factors responsible for cracked foundation walls. Water in the soil may also be the source of water leaking into a basement. However, cracks in foundation walls are generally not the primary cause of water leaks. There are also other potential causes of water infiltration into a basement. Therefore, although increased pressure from water (against foundation walls) is relative to this discussion, the topics of water infiltration (leaks) into a basement and waterproofing should be discussed separately.

Much information provided online about this topic (cracked foundation walls) is grossly misleading or totally incorrect. Many descriptions tend to be vague, confusing or off-topic. Examples of incorrect online information are provided at the end of this discussion.

DISCOVERY OF FOUNDATION CRACKS
Cracks in foundation walls typically occur within several years after a house is built, although there are exceptions (such as tree roots). Owners often do not notice cracks until many years after initial formation. This is especially the case in dark basements. The most dangerous situation is when cracks occur in foundation walls when the basement is finished. Although catastrophic failures are relatively rare, cracked-wall conditions can progress over time to total foundation wall failure without anyone seeing the progression.

Cracks in foundation walls often become a major issue when discovered by a home inspector during a pre-purchase inspection. Although the owner usually contends a cracked wall has been that way “forever”, a buyer tends to become concerned when confronted with a warning in the inspection report. Homeowners selling a house often attempt to cover-up foundation cracks by painting the wall or filling cracks with flexible caulking. A qualified, experienced home inspector should highlight any such attempt in the home inspection report.

BASIC TYPES AND CAUSES OF CRACKS
Cracks are generally considered vertical, horizontal or “diagonal” (sloped), even though most cracked-wall conditions include all three categories.

Narrow vertical cracks are most often caused by minor settlement or normal shrinkage. Such cracks are not structural defects. Wide vertical cracks (such that the thickness of a 25-cent quarter coin can be inserted) may be caused by significant settlement problems that require detailed engineering inspection and evaluation. In concrete walls, you will almost always find numerous, very narrow (“hairline”) vertical cracks. These cracks are caused by normal shrinkage of concrete and are not a structural defect. Foundation walls built with concrete block (often, and incorrectly, described as “cinder” block) are much more likely to be cracked than solid concrete walls, especially if the block wall is constructed of 8-inch block.

Horizontal cracks are much more of a concern than vertical cracks, especially in block foundation walls. Foundation walls must of course support the vertical weight of a building. Foundation walls around a full basement must also resist inward (lateral) pressure from soil against the wall. If soil (backfill) becomes saturated with water, inward pressure can easily overload a block wall, resulting in cracks. Excessive inward lateral pressure against a block foundation wall all too often causes horizontal cracks in mortar joints. Telltale sign of excessive lateral soil pressure is a horizontal crack, about mid-height of the wall. Towards the ends of a straight foundation wall segment (near corners), horizontal cracks transition into “step” cracks, which are short vertical and horizontal cracks.

The building code includes standard limits for height of “unbalanced” backfill soil against a concrete block or plain concrete foundation wall. For an 8-inch hollow concrete block wall, height of backfill (above basement floor slab) is limited to 4 feet. Block foundation walls often remain cracked for many years without any obvious additional cracking or inward movement (bulging). However, once a horizontal crack occurs, the structural integrity of the wall is greatly reduced. If soil backfill becomes saturated during periods of heavy rainfall, cracks can increase or, in the worst case, the entire foundation wall can collapse into the basement.

Roots from large or even moderate size trees near a foundation wall can easily cause major problems with block foundation walls. Roots tend to grow towards foundation walls because water accumulates along the wall.

BASIC REPAIR METHODS – HORIZONTAL CRACKS
Cracked foundation walls can be permanently repaired, without complete replacement, as long as inward movement is not excessive, even though evaluation of excessive movement is somewhat subjective. The key issue is whether the wall can continue to provide vertical support for the house without risk of severe damage in the even vertical loads are increased. Inward movement is typically measured relative to base of wall, using four-foot carpenter level or plumb string-line. Maximum inward movement (deflection) usually occurs at the horizontal crack and near mid-height of the wall.

If inward movement of a cracked foundation wall exceeds 1-1/2 inches, or if a hinge has occurred at the horizontal crack, consideration must be given to complete replacement of the wall. Cost for replacement is typically much greater than cost of bracing. Therefore, having repair work performed before inward movement increases is essential to minimizing repair costs. Traditional repair methods involve bracing the foundation wall with steel post-braces or reinforced block piers. Steel post-braces may be less expensive than piers, which must be placed on a concrete foundation (footing). However, piers often provide a better finished appearance.

Steel post braces must be securely connected at base and top, which is all too often neglected if braces are not designed by a qualified engineer. Steel reinforcing bars have successfully been installed (grouted) into block walls to provide adequate strength to resist soil pressure. However, this method is highly dependent on quality of workmanship. Inspection is effectively impossible once bars are in the wall. Installation of bars also requires extensive removal of inside face of block wall, which can cause damage to unseen parts of the block.

In recent years, more exotic repair methods have been developed, such as tiebacks and carbon-fiber strips. Although these methods have been used successfully, there have also been failures, as there are with any relatively new technology. Careful application of newer methods is therefore warranted.

MISLEADING AND INCORRECT ONLINE INFORMATION
Examples of errors with online information, discussed below, demonstrate why it is important to obtain information about foundation wall problems from qualified professional engineers.

INSPECTAPEDIA
Currently (10-18-09) the top link obtained from a Google search of “cracked foundation wall” is an advertisement for inspection services on the “InspectAPedia” web site.

http://www.inspect-ny.com/structure/FoundationCracks.htm
Excerpts from a “book” (that apparently is not available other than online) provide some detailed information about evaluating cracked foundation walls. At end of the web page, the apparent author (Daniel Friedman) includes a long list of persons without any clear description as to the intent. The apparent intent is that these persons are contributors or perhaps fact-checkers.
Statement of qualifications notes that Mr. Friedman is an “Educator, author, Building failures researcher” and a “Consultant specializing in construction & environmental testing & inspection.”

Although much information presented is valid and useful, some claims are confusing and misleading, as noted with the following two examples:
(1) Claim that the location (within height of wall) of horizontal cracks explains the reason for the cracks are overblown. This claim is simply not reasonable considering the wide variety of factors that can result in horizontal cracks, including workmanship, materials, and various sources of loads over long periods of time. One major source of cracks (tree roots) is completely ignored.

(2) A diagram included with “Repair Methods for Bulged Foundation Walls” is grossly incorrect. Base of the vertical steel channel is shown above the floor slab, without any connection. This is a major mistake. Base of any such vertical brace must have secure connection to the floor slab to resist horizontal force, which is greatest at base of the brace.

ASK THE BUILDER
An example of misleading and incorrect information that you might trip over online (as of 10-18-09) is the following from the “Ask The Builder” web site:

Crack Appearance: Horizontal Crack in a foundation wall. Commonly seen in concrete block walls. Crack is usually 4 to 5 feet off the floor.

Possible Cause: Poorly designed foundation wall. Wall is actually a retaining wall trying to hold back dirt from falling into basement. Can be fixed with beams or helical piers.

Description of the crack is not complete since horizontal cracks in block walls always occur in one or more horizontal mortar joints. Comment about “usually 4 or 5 feet off the floor” is not correct. Most horizontal cracks occur at or below mid-height of a block foundation wall, where the largest flexural tension stress occurs. The vast majority of residential block foundation walls are less than 8 feet high, such that height of horizontal cracks is generally less than 4 feet above basement floor slab.

Horizontal cracks can be caused by defective construction as well as defective design. While the “retaining wall” comment is correct and useful for understanding, this is true of any foundation wall, not just a wall with a horizontal crack. Most important however is that the suggested repair methods (“beams or helical piers”) are grossly inadequate and incorrect. A beam is generally a horizontal element. A foundation wall with horizontal cracks must be braced with vertical elements, against the wall. “Helical piers” (a type of steel pile) are used only to underpin a foundation wall when settlement (downward movement) is the problem. Helical piers (also known as “auger piles”) are not useful in any way to repair a foundation wall that has been cracked due to inward soil pressure.

For more articles by this author, please go to Helium.com

John F Mann, PE
Structural Support
1212 Main Street, Suite 2
Belmar NJ 07719
732-556-6080
jmann77@optonline.net

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