Residential raised floor foundations represent a hazard during an earthquake provided they are not adequately bolted and braced. The homeowner can determine if these conditions are present by:
Identifying the Sill Plate – With the use of a flashlight, the homeowner is to look at the top of the concrete footing. There will be a horizontal wood member 1 1/2 inches thick on top of the concrete footing.
Verifying the Sill Plate Bolting – The sill plate should be connected to the concrete footing with bolts spaced no more than 6 feet apart. The bold ends and the nuts should be visible above the sill plate.
Verifying the Cripple Wall Bracing – The cripple walls should be braced either by the presence of plywood sheathing nailed onto the cripple studs or with a wood element nailed diagonally across the studs.
If the sill plate is not bolted, or the cripple wall is not braced, we strongly encourage the homeowner to consider seismically retrofitting their foundation.