Cal. Code Regs. tit. 25, § 1334.4 – Footings in Areas Subject to Ground Freezing.

(a) Support footings shall be placed below the frost line depth, determined by the local jurisdiction, in areas subject to ground freezing.
(b) The lowest point of the footing shall be below the frost line on firm undisturbed soil.
(c) Footings shall be precast or poured in place concrete not less than three and one-half (3 ½ ) inches in thickness, or other approved materials listed for use below grade. The concrete shall have a minimum twenty-eight (28)-day compressive strength of not less than two thousand five hundred (2500) psi.
(d) No wood, or other non-masonry material not listed for use below grade, shall be below the surrounding grade and only pressure-treated wood and wood with natural resistance to decay and termites is permitted within six (6) inches of the soil.
(e) Holes for footings shall be open for inspection and backfilled prior to final inspection.
(f) Metal supports shall not be imbedded in soil or concrete.
(g) An additional inspection is required for verification of either footing depth or backfill, if not conducted at the time of the unit's installation.

Note: Authority cited: Sections 18300 and 18613, Health and Safety Code. Reference: Section 18613, Health and Safety Code.

1. New section filed 7-6-2004; operative 7-6-2004 pursuant to Government Code section 11343.4 (Register 2004, No. 28).