These rules apply to UNINCORPORATED Los Angeles County - communities like East Los Angeles, Altadena, Hacienda Heights, Rowland Heights, South Whittier, and Florence-Firestone - not the City of LA or the county's 88 incorporated cities, which each run their own ADU programs. The county's current ordinance (2025-0029, effective August 28, 2025) allows up to three accessory units on a single-family lot (attached ADU + detached ADU + JADU), caps new ADUs at 1,200 sq ft, and approves everything ministerially through the EPIC-LA portal under Title 22 Sec. 22.140.640. Note: where the county code conflicts with state ADU law (HCD flagged several provisions in December 2025), state standards control.
Zoning & Size Requirements [1][2]
Yes — unincorporated Los Angeles County allows ADUs. A detached ADU can typically be up to 1,200 sq ft under California state law and the County's zoning code.
See what this means for your lot — get 3 free quotes from Los Angeles County ADU builders →
| Where ADUs Are Allowed | Any lot zoned for single-family or multifamily residential use with an existing or concurrently built primary dwelling (Title 22 Sec. 22.140.640); state-exemption ADUs must be approved even in Very High Fire Hazard Severity Zones |
| Max Size (Detached) | 1,200 sq ft for new construction (conversions of existing detached structures have no maximum, +150 sq ft for ingress/egress); the 800 sq ft state-exemption ADU is approved with no local standards |
| Max Size (Attached) | 1,200 sq ft uniform limit since August 2025 (conversions entirely within the existing home have no maximum) |
| Max Size (JADU) | 500 sq ft within the single-family residence or attached garage (state standard) |
| Max Height | 25 ft for new-construction ADUs on single-family lots (state minimums of 16-20 ft still apply where a Community Standards District says less); 25 ft on multifamily lots |
| Max Units | Single-family lot: up to 3 accessory units - 1 attached ADU + 1 detached ADU + 1 JADU. Multifamily lot: converted ADUs up to 25% of existing units plus detached ADUs (state SB 1211 allows up to 8 detached, which controls over the county's 2). |
Setback & Parking Requirements [1][2]
Unincorporated Los Angeles County requires a rear setback of about 4 ft for a detached ADU, and parking requirements vary by unit size or location. Owner-occupancy is not required — you can rent it out without living on the property.
| Rear Setback | 4 ft for new construction; none for conversions or same-footprint rebuilds |
| Side Setback | 4 ft; 10 ft from a reversed corner lot line; no windows or doors within 3 ft of a property line |
| Front Setback | Standard Title 22 front setback - but an ADU of 800 sq ft or less may encroach into it if no other ground-level location exists (since Aug 2025) |
| Parking Required | None outside Very High Fire Hazard Severity Zones (and never for JADUs). In a VHFHSZ: 1 uncovered space unless exempt (near transit, ≤800 sq ft detached, conversion, historic district, car-share nearby). No replacement parking when a garage is converted |
| Owner Occupancy | Not required for ADUs. JADUs: the county requires owner occupancy via recorded covenant, but state AB 1154 (Jan 2026) bars that for JADUs with their own bathroom - state law controls |
| Min Lot Size | None - California law prohibits minimum lot sizes for ADUs |
Permit Process & Fees [3][4]
An ADU in unincorporated Los Angeles County is approved ministerially (by-right) within the state's 60-day ministerial deadline from a complete application, with a 15-business-day completeness check since January 2026 (SB 543); permit fees are valuation-based through Regional Planning and Building & Safety - no flat rate; get an estimate through EPIC-LA before budgeting.
| Approval Process | Ministerial - no hearing. File a DRP Base Application with plot plan via the EPIC-LA portal for Regional Planning review, then plan check and permit through Public Works Building & Safety; JADUs need a recorded covenant |
| Review Timeline | the state's 60-day ministerial deadline from a complete application, with a 15-business-day completeness check since January 2026 (SB 543) |
| Permit Fees | valuation-based through Regional Planning and Building & Safety - no flat rate; get an estimate through EPIC-LA before budgeting |
| Impact Fees | Development impact fees are waived for ADUs under 750 sq ft under California law (SB 543 clarified this from Jan 2026), and apply proportionally above that |
| Plan Check | Standard plan check via Building & Safety; using a pre-approved Standard Plan substantially shortens review |
| Pre-Approved Plans | Yes - the county's free Standard ADU Plans program (county catalog plus a private-designer catalog) provides pre-checked plans for unincorporated parcels |
Get Free ADU Quotes in Los Angeles County
Tell us about your project and we'll connect you with ADU builders serving Los Angeles County. Free, no obligation — you choose who to work with.
Takes about a minute.
Up to 3 independent local ADU builders — never more, and we tell them nothing you don't submit here.
Compare quotes, verify license & insurance, hire (or don't). No spam either way.
🔒 Your info is secure. We share it only with contractors quoting your project. No spam, no obligation.
Just browsing? Search ADU builders near you by ZIP code.
Construction Costs [5]
Building an ADU in unincorporated Los Angeles County typically costs $150,000-$350,000 (LA-metro market estimate) ($200-$400 (market estimate) per sq ft); a garage conversion runs $80,000-$180,000 (market estimate).
See what this means for your lot — get 3 free quotes from Los Angeles County ADU builders →
Construction costs in unincorporated Los Angeles County mirror the surrounding Inland Empire market. Rural parcels can cost more due to septic, well, access, and fire-hazard (WUI) requirements, so treat these as planning ranges and get local bids.
| Average Build Cost | $150,000-$350,000 (LA-metro market estimate) |
| Cost per Sq Ft | $200-$400 (market estimate) |
| Garage Conversion | $80,000-$180,000 (market estimate) |
| Prefab ADU (Installed) | $120,000-$270,000 (market estimate) |
Finance Your ADU Project
Most ADU projects are funded through HELOCs, construction loans, or cash-out refinancing. Compare rates from top lenders.
Some links on this page are affiliate links. We may earn a commission at no extra cost to you. Learn more
Rental Income Potential [6]
| Avg Rent (1 Bedroom) | $1,700-$2,400/mo (East LA and Florence-Firestone below Altadena/Hacienda Heights) |
| Avg Rent (2 Bedroom) | $2,100-$3,000/mo |
| Short-Term Rental | No - the county's short-term rental ordinance (effective September 2024) limits STRs to a host's primary residence and expressly bars ADUs and guesthouses from listing; the ADU ordinance separately requires rentals of 30+ days |
| Est. Annual ROI | 6-9% annual return (market estimate) |
Recent Law Changes
What's Changed Recently
- August 28, 2025: Ordinance 2025-0029 took effect - uniform 1,200 sq ft attached-ADU limit, 1,200 sq ft cap on detached ADUs on multifamily lots, state-exemption ADUs allowed in Very High Fire Hazard Severity Zones regardless of access, unpermitted structures may be converted, and sub-800 sq ft ADUs may encroach into front setbacks
- December 1, 2025: California HCD found the county ordinance partially non-compliant with state ADU law - state standards override the county code where they conflict
- January 1, 2026: SB 543 (15-business-day completeness review, impact-fee waiver under 750 sq ft) and AB 1154 (no JADU owner-occupancy where the JADU has its own bathroom; JADU STR ban) took effect
- March 3, 2026: the Board accepted a $3.8M state grant funding ADU construction for 35-50 unincorporated-area households, prioritizing Eaton fire survivors in the Altadena area; AB 462 lets fire survivors occupy a finished ADU before the main house is rebuilt
Tips for Building an ADU in Unincorporated Los Angeles County
- East LA, Altadena, Hacienda Heights, Rowland Heights, South Whittier, and Florence-Firestone are unincorporated - County rules apply, not City of LA rules
- Use the free Standard ADU Plans catalog to cut design costs and plan-check time on unincorporated parcels
- Keep the ADU at or under 750 sq ft to avoid development impact fees entirely
- In fire-hazard zones (much of Altadena and the foothills), the 800 sq ft state-exemption ADU must be approved regardless of road-access standards - a strong fallback if the county flags your access
- Eaton fire survivors: ask about the county's ADU grant program and AB 462's early-occupancy rule before waiting on the main-house rebuild
ADU Builders in Los Angeles County
Looking for an ADU builder in Los Angeles County? ADU projects need a contractor experienced with local zoning, the permit process, and utility connections — not every general contractor has built one. We match Los Angeles County homeowners with experienced local ADU contractors who provide free, no-obligation quotes. Getting at least three bids typically saves 20-40% on the same scope.
Cities Within Los Angeles County
If your property is inside one of these incorporated cities, follow that city's ADU code — not the County rules above:
Sources & References
All data on this page is sourced from official government records and verified market data. View our full methodology.
- LA County Regional Planning - ADU Ordinance Amendment certified ordinance (Ord. 2025-0029, eff. 8/28/2025) Planning Department — Accessed 2026-07-30
- LA County Regional Planning - Accessory Dwelling Units program page Planning Department — Accessed 2026-07-30
- LA County Regional Planning - ADU Ordinance Amendment FAQs Planning Department — Accessed 2026-07-30
- California HCD - ADU ordinance findings letter, County of Los Angeles (12/1/2025) Government Data — Accessed 2026-07-30
- Angi - ADU Construction Cost Data Market Data — Accessed 2026-07-30
- HUD Fair Market Rents Government Data — Accessed 2026-07-30
- California ADU Handbook - HCD Government Data — Accessed 2026-07-30
- LA County Regional Planning - Eaton Fire disaster recovery Planning Department — Accessed 2026-07-30
Frequently Asked Questions
What are the ADU rules in unincorporated Los Angeles County?
How much does an ADU permit cost in Los Angeles County?
Do I need owner-occupancy for an ADU in Los Angeles County?
Is my property in unincorporated Los Angeles County or inside a city?
How many ADUs can I build in unincorporated Los Angeles County?
Building in Unincorporated Los Angeles County?
Get free, no-obligation quotes from ADU contractors who work in Los Angeles County.
Get Free Quotes →