Why Are Cracks Appearing In My Foundation?
Do you have cracks appearing in your foundation walls? There can be many reasons for cracks to appear, some may be harmless, while others may be signs of serious problems. The Bay Area is known for earthquakes, and the constant shifting of the ground can cause a foundation to crack over time.
A foundation is the substructure on which a building rests. In The Bay Area, this is usually reinforced concrete although some elevated homes may be exceptions. The concrete sub-base can take two different forms. It could be a series of strips mirroring the walls above, or a solid sheet.
The correct application depends on the soil type. If it is stable, the strip method may suffice. However if the soil is clayey and likely to heave during wet periods, then the correct solution is a concrete “raft” that insulates the structure overhead from the movement that occurs below.
The Common Problem
Many builders design foundations on the basis that they will be stable once laid. Over time, outside forces make shift and put stress on the concrete structure:
- The earth beneath the foundations settles because it was not properly compacted in the first place and ground water flows in through the gap
- Earth movement occurs as a result of seismic events, mining activity or construction work on an adjacent site
- The ground expands and contracts during alternating wet and dry seasons, especially if it has a clay component
When foundations move and crack below, this movement transfers to the structure above where masonry courses separate. It is most likely to be evident in the vicinity of weaker points like corners and above window and door frames.
Warning Signs
Unless caused by seismic activity, masonry cracking is usually a gradual process that occurs almost imperceptibly. Early indications can include:
- Doors and windows that jam up in wet periods but begin to rattle in the wind when the weather’s dry
- Cracks stepping up the masonry courses or appearing horizontally through bricks
- In extreme cases, distorted walls and tilting chimneys
It goes almost without saying that these problems must be dealt with before serious structural damage occurs.
Remedial Action
While the ostensible cause of foundation cracking is ground movement or soil erosion, the true reason is that the foundation may be inadequate for local circumstances, or was earth around it was not settled properly before creating the foundation. Short of tearing down the structure the only practical solution is to strengthen the foundation. Foundation engineers achieve this with a variety of solutions that include steel or helical peers, plate and tie anchors, hydraulic lift slab piers and concrete underpinning.
In Summary
Cracks appear in foundations for two related reasons. Either the substructure is inadequate, or an event occurred outside the design specification. While the settlement may be slight and the visible evidence purely cosmetic, it may be the beginning of a far more serious problem if left untreated.
Some foundation cracks may not be an indicator of serious foundation problems, while others may signal the start of serious foundation problems.
