How Solid Is My Foundation?
Foundations have two primary functions: to lift your house off the ground and protect it from earthquakes.
It is understandable to be concerned about existing foundations, cracks, and earthquake performance. However, a foundation is rarely wrong off enough to warrant a replacement. Similarly, it will not make sense to replace segments of your foundation if they are decaying. Most houses have an adequate amount of strong foundation.
When an earthquake hits a seismic retrofit house, all of the force transfers into the bolts. The bolts then move the force into a soft piece of redwood in the concrete foundation. These three components hold each other accountable for keeping your house stable.
If anything were to break during an earthquake, it would be the mudsill- the delicate piece of redwood. The Structural Engineer’s Association has run many tests to prove that the strength and condition of the concrete do not affect the earthquake brace bolt in the presence of seismic activity. The primary failure of these tests was the mudsill.
How Should You Deal With Foundation Cracks?
Existing foundations, cracks, and earthquake performance have very little in common.
Almost all older home foundations have cracks. These occur when soil expands and contracts underneath old, brittle concrete. Having a few breaks is common, and there’s no reason to worry. With enough foundation for your house to remain attached, your home will stay structurally sound against earthquakes.
However, severe foundation cracks can cause floors to become uneven and cracks in stucco or plaster walls.
If you find a half-inch crack, it is likely that your foundation was heaved upward or pulled downward by half an inch due to contracting soil.
How Does An Earthquake Affect My Foundation?
Earthquakes compress your concrete foundation by pushing on the sides, not pulling up or down. Homes use concrete for foundations because it can stand against a tremendous amount of compression force.
To visualize this, imagine pushing a pencil on both ends. That is what compression on your home is like during an earthquake. Regardless of how hard you try, the pencil will not break.
California’s existing building code assumes that all old foundation buildings feature 1500 psi concrete- which is what the Structural Engineer’s Association tested. Therefore, existing concrete foundations will perform well in a retrofitted house.
Foundation Rotation
When building a house, its weight pressures evenly on the foundation, inside and out. The rotation occurs when the outer side of your foundation is drenched in moisture while the inner crawlspace is dry.
When the soil outside becomes wet and soft, the foundation starts to sink on that edge, thus pulling the inner side up.
While this may sound alarming, it will not affect your foundation’s ability to keep your house off the ground and withstand an earthquake. At most, you may notice uneven floors.
If you are looking for foundation repair in Los Angeles to help inspect your home’s existing foundations, cracks, and earthquake performance, check out the experts at Seismic Safety!