SEC. 91.9302. SCOPE.

The provisions of this division shall apply to all existing buildings of wood-frame construction, or wood-frame portions thereof, where:

A permit for construction of a new building was applied for before January 1, 1978, or, if no permit can be located, the structure is determined by the Department to have been built under building code standards enacted before January 1, 1978; and
The ground floor portion of the structure contains parking or other similar open floor space that causes soft, weak or open-front wall lines, and there exists one or more stories above.

EXCEPTIONS: This division shall not apply to any building containing three dwelling units or less if the building is used solely for residential purposes. Moreover, notwithstanding any provision of this Code, compliance with this division shall not require existing electrical, plumbing, mechanical or fire-safety systems to be altered to comply with existing code unless they constitute a hazard to life or property.

SEC. 91.9303. DEFINITIONS.

The following words and phrases, whenever used in this division, shall be construed as defined in this section. Words and phrases not defined here shall be construed as defined in Division 2 of this Code.

CRIPPLE WALL is a wood-framed stud wall extending from the top of the foundation wall to the underside of the lowest floor framing of the building.

DWELLING UNIT shall include any individual residential unit within either an R-1 or R-2 occupancy building, including a mixed-occupancy building when part of it is either an R-1 or R-2 occupancy. A dwelling unit shall include the area of a building that is occupied as a dwelling unit, whether the building is approved or unapproved for residential use.

GROUND FLOOR is any floor within the wood-frame portion of a building whose elevation is immediately accessible from an adjacent grade by vehicles or pedestrians. The ground floor portion of the structure does not include any floor that is completely below adjacent grades.

OPEN-FRONT WALL LINE is an exterior wall line, without vertical elements of the lateral force-resisting system, which requires tributary seismic forces to be resisted by diaphragm rotation or excessive cantilever beyond parallel lines of shear walls. Diaphragms that cantilever more than 25 percent of the distance between lines of lateral force resisting elements from which the diaphragm cantilevers shall be considered excessive. Exterior exit balconies of six feet or less in width shall not be considered excessive cantilevers.

QUALIFIED HISTORICAL BUILDING is any building designated or currently in the process of being designated as a "qualified historical building" as defined in Part 8, Title 24 of the California Code of Regulations.

RETROFIT is an improvement of the lateral force-resisting system by alteration of existing structural elements or addition of new structural elements.

SOFT WALL LINE is a wall line, the lateral stiffness of which is less than what is required by story drift limitations or deformation compatibility requirements of this division. In lieu of the engineering analysis required by this division to determine whether a wall line's lateral stiffness is less than the aforementioned story drift limitations or deformation compatibility requirements, a soft wall line may be defined as a wall line in a story where the wall stiffness is less than 70 percent of the stiffness of the exterior wall above for the direction under consideration.

STORY is as defined in this Code, but includes any basement or underfloor space of a building with cripple walls exceeding four feet in height.

STORY STRENGTH is the total strength of all seismic-resisting elements sharing the same story shear in the direction under consideration.

WALL LINE is any length of a wall along a principal axis of the building used to provide resistance to lateral loads.

WEAK WALL LINE is a wall line at the ground floor where the wall strength is less than 80 percent of the strength of the wall above in the direction under consideration.