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SEC. 91.1809.  SHALLOW FOUNDATIONS.
   (Amended by Ord. No. 182,850, Eff. 1/3/14.)
 
   Section 1809 of the CBC is adopted by reference, except Section 1809.3, 1809.4 and 1809.12 are not adopted; and, in lieu, LAMC Subsections 91.1809.3, 91.1809.4, 91.1809.7 and 91.1809.12 are added.  (Amended by Ord. No. 185,587, Eff. 7/16/18.)
 
91.1809.3.  Stepped Footing.  (Amended by Ord. No. 185,587, Eff. 7/16/18.)  The top surface of footings shall be level.  The bottom surface of footings shall be permitted to have a slope not exceeding one unit vertical in 10 units horizontal (10-percent slope).  Footings shall be stepped where it is necessary to change the elevation of the top surface of the footing or where the surface of the ground slopes more than one unit vertical in 10 units horizontal (10-percent slope).  For structures assigned to Seismic Design Category D, E or F, the stepping requirement shall also apply to the top surface of grade beams supporting walls.  Footings shall be reinforced with four 1/2 inch diameter (12.7 mm) deformed reinforcing bars.  Two bars shall be placed at the top and bottom of the footings as shown in LAMC Figure 1809.3.
 
 
Figure 1809.3
STEPPED FOUNDATIONS
 
91.1809.4.  Depth and Width of Footings.  (Amended by Ord. No. 185,587, Eff. 7/16/18.)  The minimum depth of footings below the surface of undisturbed soil, compacted fill material or CLSM shall be 12 inches (305 mm).  Where applicable, the requirements of CBC Section 1809.5 shall also be satisfied.  The minimum width of footings shall be 12 inches (305 mm).
 
91.1809.7.  Prescriptive Footings for Light-Frame Construction.  (Amended by Ord. No. 185,587, Eff. 7/16/18.)  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 LAMC Table 1809.7.  Prescriptive footings in LAMC Table 1809.7 shall not exceed one story above grade plane for structures assigned to Seismic Design Category D, E or F.
 
TABLE 1809.7
PRESCRIPTIVE FOOTINGS SUPPORTING WALLS OF LIGHT-FRAMED CONSTRUCTION
a, b, c, d, e
 
 
NUMBER OF FLOORS SUPPORTED BY THE FOOTINGf
WIDTH OF FOOTING (inches)
THICKNESS OF FOOTING (inches)
1
12
6
2
15
6
3
18
8 g
For SI: one inch = 25.4 mm, one foot = 304.8 mm
a.   Depth of footings shall be in accordance with CBC Section 1809.4.
b.   The ground under the floor is permitted to be excavated to the elevation of the top of the footing.
c.   Not adopted.
d.   See CBC Section 1908 for additional requirements for footings of structures assigned to Seismic Design Category C, D, E or F.
e.   For thickness of foundation walls, see LAMC Subdivision 91.1807.1.6.
f.   Footings are permitted to support a roof in addition to the stipulated number of floors.  Footings supporting roof only shall be as required for supporting one floor.
 
91.1809.12.  Timber Footings.  Timber footings shall be permitted for buildings of Type V construction and as otherwise approved by the Department.  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 AF&PA NDS.  Timber footings shall not be used in structures assigned to Seismic Design Category D, E or F.