One of the most common problems we see with concrete foundation walls is that they are not properly secured or connected to the floor framing. This is usually caused by a lack of toe nails connecting the floor joists to the sill plate, an inadequate number of anchor bolts connecting the sill plate to the foundation wall, or improperly placed anchor bolts which cause the sill plate to split. As this connection to the floor framing along the top of the foundation wall fails, the foundation wall tips or leans inward under the lateral soil pressure and develops significant tension cracks. The cracks that form are generally diagonal cracks at each end of the foundation wall and a vertical crack in the center. These cracks are much more pronounced and obvious than your typical shrinkage cracks (shrinkage cracks are usually 1/8″ or less in width and are generally vertical). This problem is made worse as the foundation wall height increases and as the soils behind the wall become more saturated with ground water. Proper grading down and away must be maintained to direct water away from the foundations.
Stabilizing concrete foundation walls which are shifting inward because of a failed connection between the floor framing and the top of the foundation wall can be accomplished in a number of ways. Bracing the foundation walls with vertical steel beams is effective but may be more than is required except in areas where the strength and integrity of the concrete foundation wall has been compromised by numerous cracks, this typically occurs at the ends of the foundation wall where diagonal cracking develops. Other ways to stabilize the foundation wall involve re-establishing a connection between the top of the foundation wall and the floor framing. This can be accomplished by installing properly designed angle braces, or by installing continuous 2x material to the underside of the floor joists and tight against the foundation wall. This may not be feasible if there is interference with utilities. In some cases, if access allows, the floor joists can be toe nailed into the sill plate.
Foundation Walls Not Properly Secured By Beam Lines
Foundation walls which run parallel to the floor framing typically rely on the beams which support the floor framing being pocketed into the foundation wall to provide lateral resistance against soil pressure. Another problem we see with concrete foundation wall stability, that is not so common, is where the concrete around the beam pocket fails as the foundation wall is forced inward by the lateral soil pressure, or the beam line may not be continuous across the basement so it is free to shift as the foundation wall moves inward under the lateral earth pressure. The foundation wall cracks that develop are the same as those that develop when the floor framing is not properly connected to the foundation wall as discussed above. Bracing is typically accomplished with vertical steel beams tied into newly installed solid bridging. If installation of bridging is not possible, then tie backs may be required.
Framed Knee Walls
Foundation instability can also result from a framed knee wall being constructed on top of a concrete wall. The problem with this configuration is that the connection between the concrete foundation wall and the framed knee wall acts as a hinge and the concrete foundation wall is free to rotate inward as the lateral soil pressure pushes against the concrete foundation wall. This is generally not a problem where the exterior grade is 3′-6″ or less up along the concrete wall, and if the wall length is not relatively long. This situation can be stabilized using vertical beam braces or tie backs. If the foundation wall needs to be pushed back to a plumb position the exterior will have to be excavated to relieve the soil pressure.
Deterioration of The Sill Plate
Deterioration of the sill plate can result in the connection between the floor framing and the top of the foundation wall becoming compromised. This may result in the foundation wall moving inward under the lateral soil pressure. This situation can be stabilized using vertical beam braces or tie backs. If the foundation wall needs to be pushed back to a plumb position the exterior will have to be excavated to relieve the soil pressure.