By Tom Feiza, Mr. Fix-It, Inc.
Concrete block full-depth foundations can effectively create a basement space and support a home. However, block foundations are subject to cracking and horizontal movement if the surrounding soil is poorly drained. Poor maintenance of grading, gutters, and downspouts can also make basement walls move, and frost can push them inward. Be aware of local conditions and knowledgeable about construction or repair issues with block basements.
Check all exposed basement walls with a level to ensure they are plumb. Movement of more than ¾ inch in 4 feet vertically or horizontally as well as horizontal and step cracks can signal a serious inward movement problem. As the wall pushes in, the horizontal crack develops, and then step cracks occur when the wall separates from the corner (photo – Horizontal and Step Cracks). This problem often signals the need for inspection by a specialist.
One common repair method
How are displaced and cracked walls repaired? Interior steel braces with site-specific engineering are a common repair method in my area (illustration B035). Interior structural steel tubes are placed against a displaced wall and bolted to the joist framing. At the base, braces are bolted through the floor into the footings.
Beams are spaced at 36 to 48 inches, and the gap to the wall is filled with cement grout. Cracked mortar joints are removed and re-pointed. While this method does not straighten a wall, it restores structural integrity and prevents further movement.
When braces are placed on a beam end wall with joists parallel to the wall, the beams are attached to blocking between joists (illustration B036). The blocking is then extended back at least three joists to prevent them from twisting and moving horizontally.
Follow up if you spot those conditions
If you spot this type of repair during your inspection, suggest that the buyer obtain details from the seller on the engineering analysis and contracted repair. Often there is a guarantee on the repair. When in doubt, recommend that the buyer obtain a specialty inspection.
When inspecting a block basement with interior braces, check for rusting or movement of the steel braces, fasteners, and joist (photo – Beams on Basement Walls). Walls that have been braced should not move. Any new cracking in the mortar joints indicates ongoing movement since the repair, which could present a serious problem.