Same zip, different jurisdiction: this page covers LA County Public Works (DPW). The same zip code(s) also cover parts of Monrovia (Monrovia (its own permits)). Verify your parcel's jurisdiction before filing, different agencies, different rules.
San Gabriel Valley · LA County (Unincorporated)
ADU permits in South Monrovia Islands
Zip codes:91016
South Monrovia Islands is a small unincorporated 'island' community of about 2,500 people in the central San Gabriel Valley, scattered as multiple unincorporated pockets within the City of Monrovia and adjacent cities. It is not a city. Building permits run through Los Angeles County Public Works (Building & Safety).
Unincorporated LA County, not LADBS
South Monrovia Islands is unincorporated territory. Building permits go through LA County Public Works (Building & Safety) ↗ under LA County Code Title 22, not the Los Angeles Department of Building and Safety (LADBS). Our address checker pulls real feasibility data for any LA County address; the South Monrovia Islands-specific permit pathway is detailed below.
South Monrovia Islands by the numbers
Rounded figures from the 2020 US Census, LA County Assessor parcel data, and LA County DPW permit records.
Population
2,500
2020 Census
Single-family homes
~700
LA County Assessor
Median lot size
6,400 sqft
Approximate
ADU permits filed 2025
~12
Source: HCD 2025 total (1,278) distributed proportionally across 2024 per-area shares. 2024: 14.
What makes South Monrovia Islands different
South Monrovia Islands is one of LA County's classic 'unincorporated islands', pockets of unincorporated land surrounded by incorporated cities. Permits run through LA County DPW Building & Safety at the Alhambra office. Parcel-by-parcel jurisdiction verification is essential.
LA County ADU rules for South Monrovia Islands
Last verified: 2026-04-15
Current LA County rules from Title 22 of the County Code, as applied to South Monrovia Islands. State preemption (Gov Code §§ 66310-66342) means the county can't reduce below the state baseline. We note where that applies.
| Max detached ADU size | 1,200 sqft (state default) |
| Max ADU height | 16 ft / 18 ft with second-story setbacks |
| Setbacks | 4 ft side / 4 ft rear (state minimum) |
| Permitting agency | LA County Public Works (Building & Safety), Alhambra office |
| Local processing time | 60 days from complete submittal (state-mandated) |
Active overlays + extra rules in South Monrovia Islands
LA County overlays + state-level designations that hit a meaningful share of South Monrovia Islands parcels.
Watch-outs specific to South Monrovia Islands
- 01
'Island' jurisdiction, parcel-by-parcel verification essential
South Monrovia Islands is a patchwork of unincorporated pockets within Monrovia + adjacent cities. Neighbors a few houses apart can be in different jurisdictions.
Amenities + civic services in South Monrovia Islands
Parks, libraries, and the school district that serve the area. Context that matters for renter appeal, family relocation, and long-term resale.
Public schools
School assignments vary by exact address. Performance levels below are from the official California School Dashboard, California's official accountability system uses colored levels (blue highest, red lowest) rather than 1-10 numeric scores.
District
Monrovia Unified School District
Getting around South Monrovia Islands
Walkable + Metro A Line nearby.
Transit + walkability
Bus lines
- Foothill Transit 187
Nearest rail
Metro A Line (Gold), Monrovia Station (about 1 mi)
Walkability
Moderately walkable.
Nearby airports
Distance + type for each major Los Angeles-area airport reachable from South Monrovia Islands. Useful for travel, commute, and any flight-path noise concerns on specific parcels.
Hollywood Burbank Airport (BUR)
~13 miRegional / domestic
Nearby areas to South Monrovia Islands
Other Los Angeles-area pages worth a look. Each one runs different Accessory Dwelling Unit (ADU) rules depending on jurisdiction, we show you what changes when you cross a city or county line.
LA County unincorporated
Mayflower Village →
Small premium-mid-tier SGV unincorporated community between Arcadia + Monrovia. LA County jurisdiction shapes the Accessory Dwelling Unit (ADU) permitting path.
LA County unincorporated
Altadena →
Altadena's large historic lots and Los Angeles County jurisdiction (LADBS rules don't apply here) make Accessory Dwelling Unit (ADU) economics attractive, but the active rebuild context, Very High Fire Hazard Severity Zone (VHFHSZ) rules, and county-not-city permitting all add complexity worth understanding upfront.
LA County unincorporated
East Pasadena →
Premium small unincorporated community east of Pasadena. LA County (not Pasadena city) jurisdiction + premium Pasadena-adjacent home values shape Accessory Dwelling Unit (ADU) economics.
Frequently asked questions about South Monrovia Islands ADUs
›Can I build an ADU in South Monrovia Islands?
Yes. South Monrovia Islands allows ADUs under LA County Code Title 22, aligned with California Gov Code §§ 66310-66342. Most single-family lots can host one ADU plus one JADU. Permits go through LA County Public Works (Building & Safety), not LADBS, since South Monrovia Islands is unincorporated territory rather than a city.
›Why does South Monrovia Islands use LA County rules instead of LA City rules?
South Monrovia Islands is unincorporated. It's never been formally incorporated as its own city, so LA County serves as the local government. Building permits, zoning, sheriff, libraries (in many cases), and most other services run through county departments rather than city ones.
›Where do I submit my South Monrovia Islands ADU permit?
Online via LA County's EPIC-LA portal, or in-person at the LA County Public Works Building & Safety counter in Alhambra (900 S. Fremont Avenue). The EPIC-LA online portal handles most ADU submittals end-to-end, so you rarely need to visit in person.
›How long does the ADU permit process take in South Monrovia Islands?
LA County DPW targets the state-required 60-day plan check for ADUs from a complete submittal. Hillside, VHFHSZ, or environmental-review parcels can extend timelines by 4 to 12 weeks. South Monrovia Islands-specific overlays may add additional time. See the watch-outs above.
›Are LA County's pre-approved ADU plans free?
Yes. LA County maintains three pre-approved standard ADU plans (Plans A, B, and C) usable in any unincorporated area, including South Monrovia Islands. They're free to use, similar to LADBS's YOU-ADU program. The trade-off is reduced design flexibility, but for a fast, low-cost permit path they're the strongest option.
Ready to see what your South Monrovia Islands lot can do?
Our free address checker pulls real zoning, overlay, and parcel data for any Los Angeles County address, including unincorporated South Monrovia Islands. Start there and we'll surface what applies to your specific lot.
Check your address →Reviewed by Yair Harpaz, Founder, PermitPathLA. California DRE-licensed broker with 30+ years of Los Angeles real estate and mortgage industry experience.
South Monrovia Islands ordinance data last reviewed .
See an error or stale rule? corrections@permitpath.la
Primary sources: LA County DPW ADU info · LA County Code Title 22