There can be many reasons why your home’s foundation list may need to be strengthened, including:
* The foundation has shifted or moved due to earthquakes
* Soil has eroded beneath or around the foundation, causing cracks, sloping or sinking
* You want to add a second story to the existing structure, which will exceed the amount of weight the building and foundation can support
* The foundation has decayed over time
* There has been a change in how the structure is being used
* The soil was poorly compacted when the home was built
* Weak and poor quality materials were used when the home was built
* A basement has been added to the structure
* A new building has been constructed near the home with a deeper foundation
* The foundation has settled due to poor soil conditions or a lowered water table
In Los Angeles, homes that were constructed before 1940 were not bolted to their foundations. During an earthquake, these structures can be easily shaken off their foundation. Many homes that were built after 1940 used weak materials on cripple walls. A cripple wall is the wall that surrounds the crawl space under a house and connects the home to the foundation.
If you live in an older home, bolting the house to your foundation is critical for earthquake preparedness. The bolts should be placed every 4 to 6 feet and more than one foot away from every joint. For homes that are built on a hill, make sure you also bolt the wood that is “stepping down” on the grade.
Underpinning can also increase the strength and stability of your foundation. The process involves either extending the foundation in depth or breadth so it rests on stronger soil or distributes its load across a broader area.
Using concrete foundation repair is one of the primary methods used for underpinning. Sections beneath or around the home are excavated and then filled by the concrete. The concrete is usually mixed with aggregates. Once the concrete is poured, it will typically take 2 days to set.
Other ways of underpinning involves the use of screw piles, brackets and beams. Sometimes the soil can be strengthened by adding grout.
The strength of cripple walls can be increased with plywood. How do you know if your cripple wall needs strengthening? If the exterior of your cripple wall is made of wood siding or stucco, it will need to be strengthened with plywood. The plywood should be nailed to the walls on every side of the house.
In addition to stabilizing a home and preventing future damage, strengthening a foundation will make the structure much safer to live in, as well as easier to insure and sell.