Los Angeles County Municipal Code Ch. 18 Soils and Foundations

SECTION 1807 - FOUNDATION WALLS, RETAINING WALLS AND EMBEDDED POSTS AND POLES

1807.1.4   Permanent wood foundations systems.

Permanent wood foundation systems shall be designed and installed in accordance with AWC PWF. Lumber and plywood shall be preservative treated in accordance with AWPA U1 (Commodity Specification A, Special Requirement 4.2), and shall be identified in accordance with Section 2303.1.9.1. Permanent wood foundation systems shall not be used for structures assigned to Seismic Design Category D, E, or F.

(Ord. 2025-0047 § 29, 2025.)

1807.1.6   Prescriptive design of concrete and masonry foundation walls.

Concrete and masonry foundation walls that are laterally supported at the top and bottom shall be permitted to be designed and constructed in accordance with this section. Prescriptive design of foundation walls shall not be used for structures assigned to Seismic Design Category D, E, or F.

(Ord. 2025-0047 § 30, 2025.)

Retaining walls shall be designed in accordance with Section 1807.2.1 through 1807.2.4. Retaining walls assigned to Seismic Design Category D, E, or F shall not be partially or wholly constructed of wood.

(Ord. 2025-0047 § 31, 2025.)

1807.3.1   Limitations.

The design procedures outlined in this section are subject to the following limitations:

The frictional resistance for structural walls and slabs on silts and clays shall be limited to one-half of the normal force imposed on the soils by the weight of the footing or slab.

Posts embedded in earth shall not be used to provide lateral support for structural or nonstructural materials such as plaster, masonry or concrete unless bracing is provided that develops the limited deflection required.

Wood poles shall be treated in accordance with AWPA U1 for sawn timber posts (Commodity Specification A, Use Category 4B) and for round timber posts (Commodity Specification B, Use Category 4B). Wood poles and posts embedded in direct contact with soil shall not be used for structures assigned to Seismic Design Category D, E, or F.

Wood poles and posts embedded in accordance with Methods 2 and 3 of Section 1807.3.3 shall not be permitted for structures assigned to Seismic Design Category D, E, or F, except when used to support nonhabitable, nonoccupiable structures such as fences when approved by the Building Official.

(Ord. 2025-0047 § 32, 2025.)

SECTION 1809 - SHALLOW FOUNDATIONS

. . .

For structures assigned to Seismic Design Category D, E, or F, the stepping requirement shall also apply to the top surface of continuous footings supporting walls. Footings shall be reinforced with four No. 4 reinforcing bars. Two bars shall be located at the top and bottom of the footings as shown in Figure 1809.3.

(Ord. 2025-0047 § 33, 2025.)

FIGURE 1809.3 STEPPED FOOTING

(Ord. 2025-0047 § 34, 2025.)

Where a specific design is not provided, concrete or masonry-unit footings supporting walls of light-frame construction shall be permitted to be designed in accordance with Table 1809.7. Prescriptive footings in accordance with Table 1809.7 shall not be used to support structures that exceed one story above grade plane and are assigned to Seismic Design Category D, E, or F.

(Ord. 2025-0047 § 35, 2025.)

TABLE 1809.7 PRESCRIPTIVE FOOTINGS SUPPORTING WALLS OF LIGHT-FRAME CONSTRUCTIONa, b, c, d, e

. . .

c [Reserved].

. . .

g [Deleted].

(Ord. 2025-0047 § 36, 2025.)

Timber footings shall be permitted for buildings of Type V construction and as otherwise approved by the Building Official. Such footings shall be treated in accordance with AWPA U1 (Commodity Specification A, Use Category 4B). Treated timbers are not required where placed entirely below permanent water level, or where used as capping for wood piles that project above the water level over submerged or marsh lands. The compressive stresses perpendicular to grain in untreated timber footings supported upon treated piles shall not exceed 70 percent of the allowable stresses for the species and grade of timber as specified in the ANSI/AWC NDS. Timber footings shall not be used in structures assigned to Seismic Design Category D, E, or F.

(Ord. 2025-0047 § 37, 2025.)

SECTION 1810 - DEEP FOUNDATIONS

1810.3.2.4   Timber.

Timber deep foundation elements shall be designed as piles or poles in accordance with ANSI/AWC NDS. Round timber elements shall conform to ASTM D25. Sawn timber elements shall conform to DOC PS-20. Timber shall not be used in structures assigned to Seismic Design Category D, E, or F.

(Ord. 2025-0047 § 38, 2025.)