Cripple walls are wooden stud walls on top of the exterior foundation. The diagram on the left shows how these cripple walls may be braced with plywood.
Cripple walls are used to support a dwelling between the concrete foundation and the floor of a dwelling and to elevate the dwelling above ground to allow access to the utility lines or to level a dwelling built on a slope. Crawl space is the area created underneath the floor. The height of a cripple wall generally ranges from 14 inches to 4 feet. Typically, buildings with a “cripple wall” have 3 or more steps to the first floor. Cripple walls are typically found on dwellings built prior to 1960. Many newer dwellings utilize concrete perimeter walls to elevate or level the dwelling. These are not cripple walls. A dwelling built on a flat concrete slab without a crawl space beneath it will not have cripple walls.
Unbraced Cripple Walls
Unbraced cripple walls may collapse with the side to side swaying of the house during an earthquake, causing the house to fall. The picture you will find below shows a typical unbraced cripple wall that poses an earthquake hazard.
Cripple Walls are usually being braced by adding new lumber as backing to create solid edges for the shear wall nailing, and also the expansion bolts in place and the framing anchors connecting the rim joist to the top of the cripple wall.
Bracing the cripple walls by using structural-grade plywood is simple and provides greater resistance to earthquakes. Connect Us to get your home retrofitted.
Wooden Floors and Stud Walls
Wooden floors and stud walls are generally built on top of an exterior foundation to support a house and create a crawl space.
These are called cripple walls and they carry the weight of the house, as we talked about in the previous sections.
During an earthquake, these walls can collapse if they are not braced to resist horizontal movement If the cripple wall fails, the house may shift or fall.
How to Identify
There are several steps to go through to identify the cripple walls of your buildings.
Before the main process, go under the house through the crawl space, to see if there are any cripple walls. If there are cripple walls, check to see if they are braced.
- There should be plywood panels adequately nailed to the studs OR there should be diagonal wood sheathing.
- If you have neither of these, the cripple walls are probably insufficiently braced or unbraced.
- Horizontal or vertical wood siding is not strong enough to brace cripple walls.
Plywood, or other wood products allowed by code, should be nailed to the studs.
The following are important:
- Type of wood product used
- Plywood thickness
- Nail size and spacing
- Do not cover vents.
Consult your local Building Department for permit requirements before starting work.