What Is Cripple Wall?
Acripple wall is less than a full story height built to support the home between the concrete foundation and the first floor. These are the short stud walls that enclose the crawl space created to allow access to utility lines or to level a home built on a slope. The height of a cripple wall can be up to 4 feet and usually has steps built to the first floor. This kind of wall is designed to be able to receive the full force of a building. Many homes on the west coast were built with cripple walls when there was no building code or the building code had no provisions for making a home earthquake resistant. Many homes built with cripple walls pre-1960 have since been retrofitted to protect the structure of the home from future earthquake threats. Homes built after 1960 are now usually constructed with concrete perimeter walls to elevate them to create a crawl space or simply exist on a flat concrete slab. Turning a cripple wall into a shear wall reduces the risk of collapse during an earthquake.
How Do I Know If My Cripple Wall Is Safe?
Retrofitting your home can greatly reduce the risk of damage that can render a home unsafe to live in after a catastrophic earthquake hits. Many homeowners find themselves having to relocate to temporary housing when their home has been put to the test from ground forces that have torn it apart. If you live in an area that is prone to earthquakes, it’s important that the structural frame of your home is strong enough to absorb the energy of an earthquake. After much scientific research, advances in structural engineering have paved the way for the development of new construction techniques that better equip homes to withstand an earthquake. Local and regional building codes now require all new houses to meet these higher construction and safety standards. New provisions have been introduced for raised floor or cripple foundations by the International Existing Building Code (IEBC) intended to improve the seismic performance of a home’s structure and greatly reduce the risk of earthquake damage.
You can check with your local building department to see if your home meets these guidelines.
There are some immediate steps you can take to examine the condition of your cripple walls and how fit they are currently to withstand an earthquake. Start by entering your crawl space with adequate lighting.
Check The Mud Sill
Check to see if the wood that rests directly on the foundation, called the mud sill, is bolted to the foundation. If not, this creates a serious structural weakness that can cause your home to slide off of the foundation during an earthquake. The mud sill should be bolted at 4 to 6 feet intervals and at one foot of every joint, but no closer than nine inches to the end of the board. Bolting your mud sill to the foundation and adding plywood to the cripple walls are the two most cost effective steps you can take to strengthen your home to withstand earthquakes. If the cripple wall’s exterior is covered with only stucco or wood siding, you’ll need to add plywood to make sure the cripple walls are supported adequately.
Check For Structural Weakness
When concrete foundations are porous or crumbly they create a hazard. Unstable brick or stone masonry may need to be replaced or strengthened. Look for insect damage and dry rot areas in the wood. Cracks wider than ⅛”, large voids or “honeycomb” concrete should be repaired. Make sure to check for water damage as well. If the concrete chips or flakes when you poke at it with a screwdriver, your home could be unsafe and need immediate attention.
Once you’ve assessed the extent of your home’s integrity, you may need an expert to design these types of repairs for your home. There are architects, engineers and pest control specialists that can design a retrofitting plan and help guide you through the process.