Thousand Oaks, CA Fence Regulations: Retaining Walls (2026)
Key Facts
- Permit-exempt height
- 4 feet, footing to top of wall
- Exempt retention depth, no surcharge
- 36 inches above grade
- Exempt retention depth, with surcharge
- 18 inches above grade
- Minimum slope setback for footings
- 5 feet or per Figure 1808.7.1
- Enforcing office
- Building Official, City of Thousand Oaks
- Governing ordinance
- Ord. 1741-NS, eff. Jan. 1, 2026
Summary
Thousand Oaks requires a building permit for most retaining walls under TOMC § 8-4.09. A wall stays permit-exempt only if it is 4 feet or less from footing bottom to top, doesn't extend a downslope yard, and keeps soil retention depth to 36 inches without a surcharge or 18 inches with one.
Retaining walls that are not over 4 feet (1219 mm) in height measured from the bottom of the footing to the top of the wall, not extending a yard on a downslope and/or with a soils retention depth of: (i) Thirty-six (36") inches maximum above grade without a surcharge or (ii) Eighteen (18") inches maximum above grade with a surcharge or supporting a slope.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: 2026 S-78: 2026 S-78 Supplement contains: Current city legislation passed through March 31, 2026).
Full Breakdown
09(b)(3), the City's amended Building Code exempts a retaining wall from a building permit only when it meets every one of three conditions at once: the wall is not over 4 feet (1219 mm) measured from the bottom of the footing to the top of the wall, it does not extend a yard on a downslope, and its soil retention depth is capped at 36 inches above grade without a surcharge or 18 inches above grade if it carries a surcharge or supports a slope.
Any wall that exceeds the height cap, extends a downslope yard, or retains soil beyond those depth limits needs a building permit reviewed by the Building Official before construction. Because retaining walls sit within the City's amended California Building Code chapter, plans submitted for a permitted wall go through the same plan-check process as other structural work, and the Building Official can require engineering calculations to support the design. 1 or 5 feet, whichever is greater, unless a soils engineering or engineering geology report justifies less, and it lets the Building Official approve a retaining wall specifically to reduce that slope setback.
14, charged per the Council's adopted fee schedule, separate from any building permit fee for the wall itself. 09 was adopted by § 3 of Ordinance 1741-NS, effective January 1, 2026, as part of the City's current three-year Building Code adoption cycle.
Violations & Fines
Building a retaining wall over the 4-foot/36-inch/18-inch exemption thresholds without a permit is unpermitted work under the Building Code adopted in TOMC Chapter 4 of Title 8. The Building Official can red-tag construction, require removal or retrofit engineering, and withhold final approval on any related permit until the wall is brought into compliance or torn out. Property owners remain liable for damage the wall causes to neighboring property regardless of permit status.
Frequently Asked Questions
Do I need a permit for a 3-foot retaining wall in Thousand Oaks?
What counts as the height of a retaining wall under city rules?
Can a retaining wall reduce a required slope setback?
Sources & Official References
Other rules in Thousand Oaks
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