San Marcos | Ridgelines and Hillsides
San Marcos, California Ridgelines, Hillsides and the Airport Overlay: Ridgeline Setbacks, Height, Grading, the Ridgeline Development Permit, Slope Lot Sizes and McClellan-Palomar Airport Rules
San Marcos sits among hills, and three parts of its code add rules for lots on or near them. The Ridgeline Overlay Zone in Chapter 20.260 protects the City's main ridges. The gross slope analysis in Section 20.300.040 makes lots larger on steep land. And the Airport Overlay Zone in Chapter 20.265 adds a review for land under the flight area of McClellan-Palomar Airport. An overlay zone is a second layer of rules placed on top of the base zone of a lot; both apply, and Section 20.260.110 says that where they conflict "the more restrictive shall apply." The rules are in the San Marcos Municipal Code. The San Marcos overview has the summary.
San Marcos hillside rules in six facts
- No building may stand within 100 vertical feet of a primary ridgeline or 50 vertical feet of a secondary ridgeline, unless the Planning Commission approves a modification. Source: San Marcos Municipal Code 20.260.050(E)(1)(e)
- New buildings and additions in the Ridgeline Overlay Zone may not exceed 28 feet, or 24 feet for a building approved inside the vertical setback. Source: San Marcos Municipal Code 20.260.050(E)(1)
- Two or more main buildings or lots in a ridgeline setback area need a Ridgeline Development Permit approved by the Planning Commission. Source: San Marcos Municipal Code 20.260.060(A) and (C)
- Grading in the Ridgeline Overlay Zone is limited to no more than 25 percent of the lot area. Source: San Marcos Municipal Code 20.260.050(D)(1)(c)
- On a 15 to 25 percent slope, the minimum lot in R-1-10 and R-1-7.5 is 20,000 square feet, and at 25 percent or more it is one acre. Source: San Marcos Municipal Code, Table 20.300-2
- Every permit, including a building permit, in the McClellan-Palomar Airport Influence Area goes through Site Development Plan Review. Source: San Marcos Municipal Code 20.265.030(A)
Where the Ridgeline Overlay Zone Applies
Chapter 20.260 "shall become effective February 14, 2006" and aims "to preserve Primary Ridgelines in their natural state and minimize visual impact to Secondary Ridgelines." A primary ridgeline is "the centerline or crest of the predominant ridge of a mountain", and a secondary ridgeline is "the centerline or crest of a ridge descending from a primary ridgeline." The ridgelines are drawn on three area maps:
- North City Area #1, in the College Area Community Plan and Twin Oaks Valley Community, "which includes portions of "P" Mountain and Owens Peak."
- South East and West City Area #2, in the Questhaven/La Costa Meadows Community Plan, which includes Franks Peak and Mount Whitney, and also "Double Peak and Cerro de Las Posas as defined by the San Elijo Hills Specific Plan."
- Southern City Area #3, also in the Questhaven/La Costa Meadows Community Plan, with "a southerly primary ridgeline extending from east to west near the San Marcos abandoned landfill."
The City judged the ridges from listed "viewing platforms": points along Twin Oaks Valley Road, State Route 78 and Borden Road, seven City parks, and Cesar Chavez Plaza at California State University San Marcos. Projects near a ridgeline may need a photo simulation from those points. Check the area maps (Figures 20.260-1 to 20.260-3) or ask the Planning Division whether a lot is in the overlay before you buy.
Primary and Secondary Ridgelines
| Rule | Primary ridgeline | Secondary ridgeline |
|---|---|---|
| Vertical setback | 100 feet below the crest | 50 feet below the crest |
| Structures and grading in the setback | None, unless exempt or modified | None, unless exempt or modified |
| Uses outside the setback | Uses permitted by the zone, if they meet the chapter | Single-family large-lot homes; clusters allowed in large-lot zones |
| Temporary or portable structures | Barred in the setback | Placed to avoid views of the primary ridgeline |
| Wireless facilities | Barred in the setback | Barred in the setback |
Source: San Marcos Municipal Code Table 20.260-1 and Section 20.260.050(E).
The vertical ridgeline setback is measured downhill in height from the crest: "one hundred (100) vertical feet from primary ridgelines and fifty (50) vertical feet from secondary ridgelines." Section 20.260.050(E)(1)(e) says no new main or accessory structure shall be built inside it unless computer or photo simulation shows that the building "cannot be seen from the identified viewing platform locations or does not adversely affect the ridgeline silhouette", the Planning Commission approves a modification, and "the structure shall not exceed a height of twenty-four (24) feet."
Near the secondary ridgelines the land uses are limited to "single-family large-lot residential consistent with the underlying General Plan designation", with clusters allowed in large-lot zones. Section 20.260.050(A) says the number of homes "shall comply with the City's Slope Density Formula, even with clustering through a Specific Plan." Clustering, which puts the homes on the flatter part of a site and leaves steep land open, "shall be permitted for a residential development consisting of five (5) residential lots or more through a Specific Plan." Without clustering, lots follow the gross slope analysis.
Building and Grading Rules in the Overlay
- Height. "Build new structures or room additions to not exceed a height of twenty-eight (28) feet." Exposed basement or stem walls count in the height.
- Grading. "Grading shall be limited to no more than twenty-five percent (25%) of the lot area." Cuts and fills over 20 feet deep are discouraged, and slopes are contour graded.
- Roofs and walls. "Flat roofs are prohibited." Facades step with the slope, and underpinnings more than 6 feet above grade "shall be avoided."
- Colors. Earth tones such as "browns, greens, and terra cotta"; reflective glass and polished metal are to be avoided.
- Retaining walls. Walls higher than 8 feet "shall be divided into terraces and landscaped."
- Fences. Wrought iron or dark vinyl-clad chain-link without slats; electrified, razor and concertina wire are prohibited.
- Fire. Buildings "should be setback a minimum of twenty (20) feet from down slopes", with "A one hundred fifty (150)-foot clearance" of vegetation around structures, or as the Fire Marshal approves.
- Lighting. Flood lighting is prohibited and fixtures must be full cut-off.
- Accessory buildings. Existing ones over 400 square feet may grow by up to 25 percent; ADU size follows Chapter 20.410.
Section 20.260.050(N) adds five findings for "Projects of two (2) or more dwellings units", including that the project "Conforms to the General Plan" and "Substantially conforms to the ridgeline development guidelines." All development in the overlay must also be consistent with the City's Multiple Habitat Conservation/Subarea Plan.
Existing Homes and Exemptions
| Situation | Exempt from Chapter 20.260 if |
|---|---|
| Existing home outside the vertical setback | Additions up to 1,000 sq ft of new footprint, total up to 4,500 sq ft, height up to 28 ft |
| Existing home inside the vertical setback | Additions up to 500 sq ft of new footprint, footprint up to 3,000 sq ft, height up to 24 ft |
| Home damaged by fire, earthquake or landslide | May be rebuilt as before; only building and grading permit fees |
| New accessory building | Up to 200 sq ft of footprint and 24 ft tall |
| View fences of wrought iron or plexiglass | Up to 6 ft tall |
Source: San Marcos Municipal Code 20.260.030.
Section 20.260.030 also exempts projects whose maps, site plans or permits were issued before February 14, 2006, if nothing new is proposed or the change is in substantial conformance with the earlier approval. An exemption "does not exempt any project or parcel from Code or regulatory requirements", so the base zone rules still apply.
The Ridgeline Development Permit
Section 20.260.060(A) requires a Ridgeline Development Permit for "two (2) or more main structures or parcels located within a primary or secondary ridgeline setback area that involves grading, or construction into or onto the areas identified as the City's ROZ Map." The Planning Commission reviews and approves the permit and the building plans. One single-family home on a legal lot that meets the chapter needs no permit, but the City still gives notice. Within 20 working days of receiving the permit or the plans, the Planning Division mails a notice of intent "to the surrounding property owners within 1,000 feet of project boundary; or expand the NOI to include a minimum of one hundred (100) property owners, whichever is greater," and posts it on the City's website.
An application lists 16 items, among them a slope map at two-foot contours, a preliminary soils report, a hydrology report, an erosion control plan, a fuel management plan, a landscape plan and a materials board; "A photo simulation may be required for subdivisions of five (5) or more lots." Relief from a standard goes through the variance procedure, with the Planning Commission as the final decision maker. Its third finding reads "Granting of any modification will be adversely affect the silhouette of any ridgeline", which is missing a word; VanPlex reads it, with the purpose of the chapter, as a finding that the modification will not adversely affect the silhouette. Ask the City for its reading. A decision becomes final 10 calendar days after it is adopted unless appealed.
The permit rule meets state law at one point. SB 9 projects and lot splits must be approved "ministerially, without discretionary review or a hearing" under Government Code 65852.21 and 66411.7. A second main home on a ridgeline setback lot would trigger the Planning Commission permit in Section 20.260.060. The statute controls where the two conflict, and the 28-foot height and design rules that are objective may still apply. Get the City's position in writing before planning an SB 9 project in the overlay.
Slope Lot Sizes and the Downhill Story
Outside the overlay, steep land still changes the rules. Section 20.300.040 requires "a gross acreage analysis" in the A and R-1 zones "where the slopes may vary from relatively easy (moderate) slopes to excessive slopes." Table 20.300-2 sets the minimum lot by slope: in R-1-7.5, 7,500 square feet on flat land, 15,000 at 10 to 15 percent, 20,000 at 15 to 25 percent, and one acre at 25 percent or more. In R-2 it is 3,500, 7,500, 10,000, 20,000 and one acre over 35 percent. The lots and subdivisions page has the full table.
Section 20.300.050(A)(2) helps hill lots on height: "An additional story on the downside of any building shall be permitted for lots with an average slope greater than a one to seven (1:7) ratio (rise to run), or where no established grade exists at the property line due to the slope location of the lot." The extra story and the building design "shall be subject to Chapter 20.260." Site Development Plan Review findings in Section 20.515.060 also ask that a project "preserve natural landforms and ridgelines" and not include "excessive or unsightly grading of hillsides."
The McClellan-Palomar Airport Overlay
Chapter 20.265 regulates "land use and building design within the Airport Influence Area defined in the Airport Land Use Compatibility Plan for McClellan-Palomar Airport." Its provisions "shall prevail in all cases where regulatory conflicts exist between this chapter and any other chapter of this Zoning Ordinance." Inside the Airport Influence Area:
- Review. "All permits, including building permits, for land uses and structures within the Airport Influence Area shall be subject to Site Development Plan Review", checking FAA height and safety rules.
- FAA notice. The applicant files a Notice of Proposed Construction or Alteration with the Federal Aviation Administration, and no building permit issues until the FAA response is submitted.
- Disclosure. New subdivisions, new homes, condominium conversions and sales of existing homes in the overlay need a real estate disclosure that the property is near an airport.
- Overflight notice. Developers of new residential projects write an overflight notification document as a condition of approval.
The review step applies even to an ADU building permit, which state law requires the City to decide ministerially within 60 days. Site Development Plan Review is "an administrative process" under Section 20.515.020, but ask the City how it meets the 60-day ADU deadline in the overlay. The airport compatibility plan itself sets the noise and safety zones; VanPlex did not read it.
Best For
- ✓ Hill lots outside the Ridgeline Overlay Zone, where a downhill extra story is allowed on slopes steeper than 1 to 7.
- ✓ One new single-family home on a legal lot in the overlay, which needs no Ridgeline Development Permit.
- ✓ Existing homes outside the vertical setback adding up to 1,000 square feet of footprint.
Usually Fails When
- ✕ A plan puts any building inside 100 vertical feet of a primary ridgeline.
- ✕ A hillside subdivision assumes flat-land lot sizes without a gross slope analysis.
- ✕ A schedule leaves out the Planning Commission ridgeline permit for two or more main buildings.
What To Verify Before Spending Money
- → Whether the lot is in the Ridgeline Overlay Zone or the Airport Influence Area.
- → The average slope of the lot and the gross slope analysis result.
- → The City's written position on SB 9 projects in the ridgeline setback areas.
Where to Go Next
Related on VanPlex: the San Marcos overview, the California SB 9 page and the California property tax, fire zones and insurance page.
Frequently Asked Questions
What is the San Marcos Ridgeline Overlay Zone?
How tall can a house be in the San Marcos ridgeline zone?
Do I need a ridgeline permit to build one house in San Marcos?
Can I build an SB 9 duplex on a San Marcos ridgeline lot?
How much of a San Marcos hillside lot can be graded?
What fire rules apply to San Marcos ridgeline homes?
Can I add onto an existing home in the San Marcos ridgeline zone?
Why does a sloped San Marcos lot need a gross slope analysis?
What does the San Marcos airport overlay require?
Can a San Marcos ADU go on a ridgeline lot?
Official sources (checked October 2026)
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