house foundation 4

[rway]

My friend had a house inspected and the foundation walls are cinder block. The inspection report says the walls have come in by up to .5 inch. There are some vertical cracks and horizontal cracks. A contractor told her the horizontal cracks are more concerning than the verttical. The house is in Wisonsin. Is this foundation something to be worried about, or is less than .5 inch movement to the inside of the house ok? Also, why would horizontal be more concerning?

 

[bjb]

In my opinion this foundation is something to be very worried about. Residential foundation walls are typically not reinforced and depend on the masonry or concrete resisting the flexural tension stress. Unfortunately, masonry and concrete have relatively low tensile strengths. These foundation walls typically work by spanning vertically between the floor framing and the basement floor slab. When they crack horizontally, that means the bending strength of the wall has been exceeded, and they no longer span vertically anymore. Therefore, these cracked walls will continue to move inwards under the soil pressure from the backfill. If these walls had properly designed full height vertical reinforcing in them they would have the structural capacity to function despite cracking.

I have worked on several of these walls, and the solution that I have used is to design steel soldier beams that get connected to the floor slab and the floor framing above. These beams are fit tight to the foundation wall and resist the forces from the soil pressure. There may also be a problem with unsuitable soil being used for the foundation wall backfill and lack of a foundation drain. If these problems also exist the unsuitable material should be removed and be replaced with granular material. Definitley not cheap.

 

[jcali]

Horizontal cracks in foundation walls are usually caused by stress. As earth pushes against the wall, the wall tries to bend inward. Since the wall is supported by floors at the top and bottom, the maximum inward movement will occur near mid-height. Whe it bends inward, the inside face of the wall is subjected to tension stress. Since masonry has low tension stress capacity, a crack occurs.

This is a problem that should be addressed. There are a number of ways to address the cracking: such as vertical soldier beams placed along the inside of the wall; Drilling thru the wall and installing tie-back rods perpendicular to the wall; total wall replacement; and a relatively new idea using vertical carbon fiber strands that are adhered to the inside face of the wall. The repair method will depend on the severity, the use of the space inside, and the budget. Good luck.

-JCali