San Gabriel Valley · LA County (Unincorporated)
ADU permits in Altadena
Zip codes:9100191003
Altadena is an unincorporated community of about 42,000 people in the San Gabriel Valley (SGV), immediately north of Pasadena at the foot of the San Gabriel Mountains. It is not a city. Building permits run through Los Angeles County Public Works (Building & Safety) under LA County Code Title 22, not through a city building department or the Los Angeles Department of Building and Safety (LADBS). The January 2025 Eaton Fire destroyed roughly 9,400 structures across Altadena and northern Pasadena, and most of west Altadena is currently in active rebuild, a context that materially changes the Accessory Dwelling Unit (ADU) calculation here.
Unincorporated LA County — not LADBS
Altadena is unincorporated territory. Building permits go through LA County Public Works (Building & Safety) ↗ under LA County Code Title 22, not LADBS. Different office, different portal (EPIC-LA), similar but distinct rules.
Altadena by the numbers
Rounded figures from the 2020 US Census, LA County Assessor parcel data, and LA County DPW permit records.
Population
42,000
2020 Census
Single-family homes
~13,500
LA County Assessor
Median lot size
8,500 sqft
Approximate
ADU permits filed 2024
~95
Pre-Eaton Fire estimate from LA County DPW data. 2025 figures dramatically reshaped by rebuild permitting — see local context.
What makes Altadena different
Altadena is divided by Lake Avenue into east and west halves, with substantially different post-Eaton-Fire conditions. West Altadena was the harder-hit area; east Altadena saw lighter damage. Building permits are issued by LA County DPW Building & Safety at the Alhambra office (not at LADBS). ADU permitting in unincorporated LA County follows the state baseline (Gov Code §65852.2) implemented through LA County Code Title 22.140 — broadly similar to LADBS but with separate forms, fees, and inspectors. LA County also runs a streamlined rebuild permitting program for parcels with primary-residence loss in the Eaton Fire, including expedited ADU + primary-residence combined permits.
LA County ADU rules for Altadena
Last verified: 2026-05-12
Current LA County rules from Title 22 of the County Code, as applied to Altadena. State preemption (Gov Code §65852.2) means the county can't reduce below the state baseline — that's noted where it 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 Not LADBS. Different forms, fees, and inspectors. Online submission via EPIC-LA portal. |
| Local processing time | 60 days from complete submittal (state-mandated) LA County DPW typically meets the 60-day clock. Post-Eaton-Fire rebuild permits are on a separate expedited track. |
| Rebuild + ADU combined permits | Available for Eaton Fire affected parcels LA County's rebuild program lets affected homeowners permit a primary-residence rebuild + an ADU concurrently on an expedited track. Specific eligibility through the LA County Recovery website. |
| Pre-approved standard plans | LA County A/B/C plans available (free, county-wide) Three LA County pre-approved ADU plans usable in unincorporated areas. Free, similar to LADBS YOU-ADU. |
Active overlays + extra rules in Altadena
LA County overlays + state-level designations that hit a meaningful share of Altadena parcels.
Eaton Fire rebuild zone
~40% of parcelsWest Altadena and parts of east Altadena were significantly affected by the January 2025 Eaton Fire. LA County maintains a Recovery Permitting program with expedited review for affected parcels. ADUs are permitted alongside primary-residence rebuilds.
Very High Fire Hazard Severity Zone (VHFHSZ)
~55% of parcelsMost of north Altadena (above Altadena Drive / Loma Alta) sits in the VHFHSZ. Triggers Chapter 7A construction (Class A roofing, ember-resistant venting, fire-rated assemblies) — adds roughly 7% to construction cost on top of base ADU build.
LA County Hillside Management Area
~30% of parcelsSlopes over 25% in the northern foothills trigger LA County's Hillside Management Area rules — geotech / soils review, grading limits, and ridgeline-protection rules.
Watch-outs specific to Altadena
- 01
LADBS rules do not apply — this is LA County
If your contractor or designer assumes LADBS rules, stop and verify. Altadena is unincorporated LA County. Submittal goes to LA County DPW Building & Safety in Alhambra, not the LADBS Van Nuys or Downtown office. The codes are similar but the forms, fees, inspectors, and online portal (EPIC-LA, not LADBS PermitLA) are all different.
- 02
Post-Eaton-Fire rebuild lots have additional verification steps
If your lot had primary-residence fire damage in January 2025, the rebuild permit requires environmental clearance (debris removal verification, soil testing for ash residue) before the building permit is finalized. Most lots have already completed this through Phase 1 + 2 county debris removal — but always verify your parcel's status with LA County Recovery before paying for plans.
- 03
Altadena Library District is independent
Heads-up that the Altadena Library District is not part of LA County Library. It's a separately governed special district (a quirk dating to 1926). The two libraries on Mariposa and Lincoln are Altadena Library District; LA County Library cards are not interchangeable.
- 04
Pasadena Unified covers Altadena schools, not LA Unified
Even though Altadena is unincorporated, the school district is Pasadena Unified (PUSD) — not LAUSD. PUSD school facility fees apply to ADUs over 500 sqft.
- 05
Eaton Canyon Natural Area + trails are partially still in recovery
Eaton Canyon Falls trail and surrounding county trails were heavily damaged by the Eaton Fire. Sections have reopened in stages through 2025–26. If you're using Eaton Canyon access as a selling point for a future ADU tenant, verify current trail status with LA County Parks.
Need a person, not a wizard?
Routes that fit Altadena
Based on what we know about Altadena, these are the lead types that usually make sense here. Pick whichever fits your situation. All free, no obligation.
Rebuild context
Rebuilding in Altadena?
If your primary residence was lost in a recent fire, you can permit the primary rebuild plus an Accessory Dwelling Unit (ADU) concurrently on an expedited track. We can connect you with contractors who've done post-fire rebuilds in Altadena and understand the Los Angeles County Recovery permitting program.
See rebuild-experienced contractors →Complex permit context
Request a Altadena permit referral
Coastal, hillside, historic, fire-zone, or multi-overlay parcels in Altadena usually mean a permit expediter pays for itself in saved months. We work with vetted Los Angeles permit expediters and expeditors (both spellings) who've handled Altadena projects.
Talk to our financing broker
Want someone to walk you through your options?
Our in-house broker has 30+ years in LA mortgage and ADU financing. He'll lay out HELOC, construction-to-perm, and ADU-specific products like Renofi against your situation — free, no obligation.
Plans that fit Altadena lots
For unincorporated Los Angeles County, the LA County A / B / C pre-approved Accessory Dwelling Unit (ADU) plans are free and usable here. California Department of Housing and Community Development (HCD)-approved prefab also bypasses local plan check entirely.
Amenities + civic services in Altadena
Parks, libraries, and the school district that serve the area. Context that matters for renter appeal, family relocation, and long-term resale.
Parks + sports
Loma Alta Park
Loma Alta Drive, west Altadena
LA County Parks branch with full sports facilities. Recreation center, swimming pool, picnic areas, and a long-running summer day camp program.
Public swimming pool
- Baseball
- Basketball
- Tennis
- Soccer
- Playground
- Pool
- Picnic
- Community Center
Farnsworth Park
Lake Avenue, north Altadena
Historic 1934 WPA-built park. Davies Memorial Building amphitheater hosts community concerts and the annual Mountain Festival.
1934 WPA amphitheater
- Amphitheater
- Tennis
- Basketball
- Playground
- Picnic
Charles White Park
Fair Oaks Avenue, central Altadena
Named for the artist Charles White, who lived in Altadena. Community center, library branch nearby.
- Basketball
- Playground
- Picnic
- Community Center
Eaton Canyon Natural Area
Altadena Drive / Pasadena border
190-acre LA County Natural Area on the southwest slope of the San Gabriels. Eaton Canyon Falls trail is the main draw. Partially burned in January 2025; trails reopening in stages.
- Trails
- Picnic
Sam Merrill Trail / Echo Mountain trailhead
Lake Avenue + Loma Alta
Historic Angeles Crest National Forest trail leading to the ruins of the Echo Mountain Resort and Mount Lowe Railway. Trail damaged in the Eaton Fire; status varies.
- Trails
Libraries
Altadena Main Library
Altadena Library District
Mariposa Street, central Altadena
Independent special district library (not LA County). Established 1926. Main branch is the larger of the district's two locations.
Bob Lucas Memorial Library + Literacy Center
Altadena Library District
North Lincoln Avenue, west Altadena
Second branch of the Altadena Library District, focused on adult literacy programs.
Public schools
School assignments vary by exact address. The district + notable schools below cover most of the area.
District
Pasadena Unified School District (PUSD)
Notable schools in the area
- John Muir High School Early College Magnet
- Eliot Arts Magnet Academy
- Aveson Charter Schools (Altadena-based K-12)
- Pasadena Waldorf School (private)
Although Altadena is unincorporated, the school district is PUSD — not LAUSD. PUSD's open-enrollment magnet programs are a meaningful Altadena draw.
Getting around Altadena
Car-dependent. The Metro A Line (Gold Line) in adjacent Pasadena is the nearest rail.
Transit + walkability
Bus lines
- Metro 267 (Altadena Drive to Sierra Madre)
- Metro 264 (Lake Avenue corridor)
- Pasadena Transit Routes 31/32
Nearest rail
Metro A Line — Lake Avenue Station (about 1 mile south, in Pasadena)
Walkability
Walkable pockets around Lake Avenue + the Mariposa village; car-dependent across most of the community.
Nearby airports
Distance + type for each major Los Angeles-area airport reachable from Altadena. Useful for travel, commute, and any flight-path noise concerns on specific parcels.
Hollywood Burbank Airport (BUR)
~12 miRegional / domestic
Closest commercial airport. Easier than LAX for short trips; domestic-only.
Whiteman Airport (WHP)
~12 miGeneral aviation
Pacoima GA field. LA County is considering closure (2023 motion); future operations uncertain.
Los Angeles International (LAX)
~25 miInternational
Community + landmarks in Altadena
Annual events, landmarks, and the places that anchor the area's identity. Context for renter appeal and long-term resale.
Annual events
Christmas Tree Lane
Mid-December to early January · since 1920
Santa Rosa Avenue, lined with 100-year-old deodar cedars, lit up nightly through the holidays. One of the oldest outdoor Christmas displays in the United States; California Historical Landmark No. 990.
Source ↗Altadena Old Fashioned Days Parade
October (Saturday)
Community parade down Lake Avenue. Operated by the Altadena Sheriff's Station and local volunteer groups.
Source ↗Farnsworth Park Mountain Festival
September
Day-long festival at Farnsworth Park's 1934 WPA amphitheater. Music, food, and history exhibits about Altadena and the San Gabriels.
Source ↗
What makes Altadena Altadena
Historic landmark
Christmas Tree Lane (Santa Rosa Avenue)
0.7-mile stretch of Santa Rosa Avenue lined with mature deodar cedars planted in 1885. Annual lighting since 1920. California Historical Landmark.
Historic site
Mount Lowe Railway ruins
Hiking-accessible ruins of the 1893 Mount Lowe Railway and Echo Mountain resort, via the Sam Merrill Trail.
Landmark
Zane Grey Estate
Former home of Western novelist Zane Grey. Private but visible from East Mariposa Street.
Observatory
Mt. Wilson Observatory (Angeles National Forest, adjacent)
Historic observatory at the top of Mount Wilson, accessed via Angeles Crest Highway above Altadena. Public tours seasonally.
Nearby areas to Altadena
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.
Independent city
Pasadena →
Large bungalow-belt lots support strong Accessory Dwelling Unit (ADU) economics, but Pasadena's Landmark Districts cover a meaningful share of the city and add design-review time to any exterior-visible ADU.
LA City
Eagle Rock →
No HPOZ (rare for NELA), basin geography, Oxy-adjacent rental demand. Cleanest NELA permit path of any neighborhood.
LA City
Highland Park →
Bungalow heaven + dense HPOZ coverage. ADU permits take 2-4 months longer here than non-HPOZ LA, but the lots and demand make it worth it.
Frequently asked questions about Altadena ADUs
›Can I build an ADU in Altadena?
Yes. Altadena allows ADUs under LA County Code Title 22, aligned with California Gov Code §65852.2. Most single-family lots can host one ADU plus one JADU. Permits go through LA County Public Works (Building & Safety) — not LADBS, since Altadena is unincorporated territory rather than a city.
›Why does Altadena use LA County rules instead of LA City rules?
Altadena 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 Altadena 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 — you rarely need to visit in person.
›How long does the ADU permit process take in Altadena?
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 4–12 weeks. Altadena-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 Altadena. 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 start your Altadena project?
Permits for Altadena go through LA County Public Works (Building & Safety) via the EPIC-LA online portal. Start there for the official submission path.
Open the LA County permit page ↗