Here in the Greater Chicagoland Area, there are two main types of foundation walls - poured concrete and concrete block. Both are widely used and can be severely damaged by soil pressure on the exterior of the foundation walls.
When soil pressure against a foundation wall is greater than what the foundation wall can withstand, horizontal movement beings to occur. This movement manifests itself by cracks in the foundation walls, seepage and even above grade damage such as drywall cracking or cracking in exterior brickwork.
The repair methods for a leaning foundation wall depend on the amount that the wall has moved inward. If the movement is minimal, carbon fiber straps or steel wall braces are an appropriate repair to prevent further movement and the possibility of having to excavate and straighten the wall later. If the wall has moved significantly, the soil outside the wall will have to be excavated and the foundation wall straightened, or in the worst cases, replaced altogether.
When to Straighten a Leaning Foundation Wall?
Due to its being built of many small pieces or blocks mortared together, needs to be excavated and straightened sooner than a poured concrete foundation wall.The mortar joints between the blocks are the weakest point in a concrete block foundation wall.
Typical signs of inward movement of a concrete block foundation wall include the following: wall bowing at or near the center of the wall, horizontal cracks in the mortar joints and the blocks being displaced laterally.
A concrete block foundation wall should be straightened when the inward movement exceeds two and a half inches, the blocks shatter or if the second course of block has shifted laterally more than 1 inch. All three of these scenarios indicate that the concrete block foundation is unstable and a failure is more likely to occur.
These foundations get their strength from the fact they are a monolithic piece of concrete rather than a mosaic of small individual pieces. While very strong when compared to a concrete block foundation, a poured concrete foundation can still experience major problems when subjected to significant soil pressure.
Symptoms of inward movement on a poured concrete foundation include severe cracking of the wall, angle cracks at the ends of the wall, cracks in the corners of the wall, even the beam cracking and poking out of the foundation wall on the exterior as well as the foundation wall sliding out from under the floor joists.
The general rule of thumb for a poured concrete foundation wall is 30% of the wall thickness. This is the maximum the foundation wall can be moved inward before the appropriate course of action is to excavate and straighten the wall. Example: a ten inch thick foundation wall can be stabilized with inward movement up to three inches. Anything beyond the three inches of movement is when excavation and straightening the wall would be the repair method of choice.
The reason for these rules of thumb is that as a leaning foundation wall gets more significant, the weight of the house and gravity have a greater affect and the likelihood of a foundation wall failure increases. Foundation failure, as one would expect, not only affects the foundation, but the entire above grade structure as well.
Figuring out whether a leaning foundation wall needs to be excavated and straightened or just stabilized is the job of an experienced foundation repair contractor. At U.S. Waterproofing, our foundation repair experts use the latest techniques and information to diagnose and repair bowed, cracked or leaning foundation walls for homeowners all over Chicagoland, Southeastern Wisconsin and Northwest Indiana. Contact us for free advice on your leaning foundation wall.