BUILDING CODE MANUAL #14COUNTY OF LOS ANGELES 1808.6

DEPARTMENT OF PUBLIC WORKS Article 1BUILDING AND SAFETY DIVISION 07-12-11

Based on the 2011 LACBC Page 1 of 3

FOUNDATION REQUIREMENTS ON EXPANSIVE SOIL

ISSUE:One- and Two-Story Dwellings of Group R-3, R3.1 and R-4 Occupancies and AccessoryBuildings of Group U Occupancy

Foundation systems on expansive soils shall be designed and constructed in a manner that willminimize damage to the building from the movement of the soil. Slab-on-grade and mat-typefootings for buildings located on expansive soils shall be designed in accordance with BuildingCode Section 1808.6 or such other engineering design based on geotechnical report(s) asapproved by the Building Official. When such approved design and methods of construction arenot provided, the prescriptive requirements listed below may be used (see attached diagram):

POLICY:1. All exterior wall foundations and interior bearing wall foundations shall extend not less

than 24 inches and 18 inches, respectively, below undisturbed ground surface or finishgrade (certified fill).

2. Exterior walls and interior bearing walls shall be supported on continuous foundations.

3. Foundations shall be reinforced with a minimum of four continuous horizontal reinforcingbars. At least two 1/2 inch diameter (# 4-bar) deformed reinforcing bars shall be placedwithin four inches of the top of the footing and at least two 1/2 inch diameter (# 4-bar)deformed reinforcing bars shall be placed between 3 inches and 4 inches of the bottomof the footing.

Foundations for exterior walls and interior bearing walls shall be tied to the floor slabs byreinforcing bars (dowels) having a diameter of not less than 1A inch (# 4-bar) and spacedat intervals not exceeding 16 inches on center. The reinforcing bars shall extend at least40 bar diameters into the footings and the slab.

5. Concrete floor slabs-on-grade shall be cast over two layers of 2-inch sand fill with aminimum 6-mil moisture barrier membrane sandwiched between the two 2-inch layers.The slab shall be at least 4 inches thick and shall be reinforced with #4-bar at 16 incheson center each way.

6. The soil below an interior concrete slab shall be saturated with clean water to a depth of18 inches prior to pouring the concrete.

Note: Construction sites located within designated liquefaction zones shall comply with the morerestrictive foundation detailing requirements of BCM 1802.2.7, Article 1.

Supersedes BCM 1805.8 Article 1 dated 05-13-09

N ALAMChief Engineer

IN

(I' RAJ TEL 1Supe ntende t of Building

BUILDING CODE MANUAL Page 2 of 3#14 - 1808.6 Article 1

WRITTEN BY: JONATHAN LAM REVIEWED BY: JUAN MADRIGALCivil Engineer Senior Civil Engineer

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