Building an ADU in La Mirada. Rules, costs, timeline.

What you can build on your lot

Everything in this section is grounded in La Mirada Municipal Code § 21.54 and the California Government Code that supersedes it where the two disagree. Because the City’s 2018 text is narrower than current state law on most points, we name the local rule, then the state rule that controls. Assume § 21.54 under each heading unless we tell you otherwise.

Number of ADUs per lot

• Single-family lot. The ordinance allows only one ADU (§ 21.54.020(a)(2)) and prohibits junior ADUs outright (§ 21.54.020(a)(20)). Both limits are preempted. State law requires the City to allow a conversion ADU created from existing space, plus a junior ADU, plus a new detached ADU of up to 800 sqft — up to two ADUs and a JADU on one lot (Gov. Code § 66323(a)(1)–(2); Gov. Code § 66316).
• Multifamily lot — existing building. Conversion ADUs in non-livable space — at least one, up to 25% of the existing units — plus up to eight detached ADUs under SB 1211, not to exceed the number of existing units (Gov. Code § 66323(a)(3)–(4)). The 2018 ordinance does not contemplate this at all.
• Existing accessory structures. A detached accessory structure may be converted to an ADU — an old workshop or oversized garage can become a unit without being held to the new-construction size limits (Gov. Code § 66323(a)(1)).

Size limits

• The local 800 sqft / one-bedroom cap is preempted. § 21.54.020(a)(13)(B) caps an ADU at 800 sqft and § 21.54.020(a)(14) limits it to one bedroom. State law requires the City to allow at least 850 sqft for a studio or one-bedroom and 1,000 sqft for two or more bedrooms (Gov. Code § 66321(b)(2)) — multi-bedroom ADUs included.
• The 800 sqft unit is protected outright. An 800 sqft ADU must be allowed regardless of any FAR, lot-coverage, or open-space limit (Gov. Code § 66321(b)(3)).
• Conversion ADU: no separate square-foot cap when created within existing permitted space; a converted accessory structure may add up to 150 sqft for ingress and egress (Gov. Code § 66323(a)(1)).
• Junior ADU: up to 500 sqft inside the single-family home (Gov. Code § 66313(d)) — allowed despite the local prohibition.

Setbacks

The ordinance asks for a five-foot side and rear setback for a detached ADU (§ 21.54.020(a)(9)), but state law caps the requirement at four feet (Gov. Code § 66314(d)(7)), so four feet is the operative number. The front setback follows the underlying zone. No added setback is required for an ADU built within an existing structure, whether a conversion or a same-footprint replacement. On a typical La Mirada parcel the practical move is to set the unit in the rear yard and let the four-foot envelope do the work.

Maximum height — single story by right

The ordinance limits a detached ADU to one story and 15 feet (12 feet for a flat roof) (§ 21.54.020(a)(7)), but Gov. Code § 66321(b)(4)(A) guarantees 16 feet for a detached ADU statewide, so the lower local cap is preempted. An attached ADU may reach 25 feet or the height of the primary dwelling (Gov. Code § 66321(b)(4)(D)). For a standalone detached backyard ADU, this is a single-story market: our three two-story Signature Homes — the Fairfax, Venice, and Culver — are detached designs that need roughly a 25-foot standalone envelope, and we do not sell them as attached units, so on a La Mirada lot the right move is one of our six single-story models. La Mirada does have one unusually generous height rule of its own — a 35-foot allowance for an ADU above an existing garage — which the next section explains.

Parking

La Mirada requires one off-street parking space for an ADU (§ 21.54.020(a)(15)), waived when the ADU is within one-half mile of public transit (measured along the pedestrian path of travel), in a historic district, part of the existing primary residence, or within one block of a car-share vehicle (§ 21.54.020(a)(16)). That list tracks the state framework in Gov. Code § 66322. A junior ADU never requires parking (Gov. Code § 66334(a)). And the City’s rule requiring replacement parking when a garage is converted (§ 21.54.020(a)(15)(E)) is preempted — Gov. Code § 66314(d)(11) bars requiring replacement parking when a garage, carport, or covered space is demolished or converted for an ADU.

Lot coverage, FAR, and open space

The ordinance applies the underlying zone’s lot-coverage limit to the combined primary residence and ADU (§ 21.54.020(a)(11)), but that, and any FAR or open-space limit, is expressly subject to the 800-sqft floor: none may force an ADU below 800 square feet (Gov. Code § 66321(b)(3)). On La Mirada’s generous single-family lots these rarely bind a backyard unit, and where a tighter parcel comes into play, an 800-sqft unit is still protected.

Owner-occupancy

La Mirada’s ordinance requires the owner to occupy the primary dwelling or the ADU as a principal residence (§ 21.54.020(a)(5)(A)), recorded by a declaration of restrictions. That requirement is preempted for an ADU: Gov. Code § 66315 bars an ADU owner-occupancy mandate statewide. The recorded declaration still validly records the 30-day-or-longer rental term and the bar on separate sale, but its owner-occupancy clause is unenforceable as to an ADU. For a junior ADU, owner-occupancy now applies only when the JADU shares a bathroom with the main house — AB 1154 amended Gov. Code § 66333(b) to that effect effective January 1, 2026, well after the City’s 2018 text.

Impact fees and utility connections

No development impact fee may be charged on an ADU under 750 sqft, and state law exempts ADUs of 750 sqft or less outright (Gov. Code § 66311.5(c)). Above that threshold, impact fees are charged proportionally to the primary dwelling’s square footage — not a flat per-unit charge. The ordinance routes an ADU’s utilities through the primary dwelling’s connections (§ 21.54.020(a)(17)); where a separate connection is required, the connection and capacity charge are priced to the burden the unit actually adds.

Permitting timeline

ADU applications run as a ministerial Site Plan Review through the Community Development Department (§ 21.54.020(a)) — no public hearing, no discretionary design review, no neighbor sign-off (Gov. Code § 66317). The City must approve or deny a complete application within 60 days or it is deemed approved. SB 543 (effective January 1, 2026) adds a written completeness determination within 15 business days (Gov. Code § 66317(a)(2)(A)).

How state law overrides La Mirada’s 2018 ordinance

Because La Mirada’s ADU chapter predates the modern state framework, the list of places state law overrides it is longer than usual. Under Gov. Code § 66316 the state standard controls wherever the local text is narrower — here is what that changes for your plan.

• Junior ADUs are allowed. The ordinance prohibits them (§ 21.54.020(a)(20)), but state law requires every city to permit a JADU — up to 500 sqft inside the home (Gov. Code §§ 66333–66339; § 66313(d)). The local ban is preempted.
• You can build more than one ADU. The ordinance caps the lot at one ADU (§ 21.54.020(a)(2)). State law requires the full stack: a conversion ADU, plus a junior ADU, plus a new detached ADU of up to 800 sqft — up to two ADUs and a JADU on one single-family lot (Gov. Code § 66323(a)(1)–(2); HCD ADU Handbook, March 2026, pp. 17–18).
• No owner-occupancy for an ADU. The ordinance requires it (§ 21.54.020(a)(5)(A)); Gov. Code § 66315 bars it statewide. For a JADU, AB 1154 narrows owner-occupancy to shared-bathroom cases as of January 1, 2026 (Gov. Code § 66333(b)).
• Taller and larger than the old code. 16 feet for a detached ADU (Gov. Code § 66321(b)(4)(A)) overrides the local 15-foot cap, and the 850 / 1,000 sqft size floors plus multi-bedroom units (Gov. Code § 66321(b)(2)) override the local 800-sqft, one-bedroom limit.
• Four-foot setbacks, and no replacement parking. Gov. Code § 66314(d)(7) caps side and rear setbacks at four feet (below the local five), and Gov. Code § 66314(d)(11) bars requiring replacement parking when a garage is converted — overriding § 21.54.020(a)(15)(E).
• The 800-sqft unit is guaranteed. An 800-sqft ADU at 16 feet with four-foot setbacks must be approved regardless of lot-coverage, FAR, or open-space limits (Gov. Code § 66321(b)(3)).

Renting an ADU in southeast LA County

Plan a La Mirada ADU around 30-day-or-longer tenancy. The City’s recorded declaration of restrictions requires a rental term longer than 30 days (§ 21.54.020(a)(5)(B)) — the 30-day minimum state law lets a city set (Gov. Code § 66323(e)). Nightly and weekly short-term rental is out; the compliant model is a long-term lease or a furnished mid-term rental — corporate, traveling-medical, or academic tenants.

For a sense of the ceiling, the federal Fair Market Rent benchmark for the Los Angeles–Long Beach–Glendale area — which includes La Mirada — runs about $2,328 for a one-bedroom, $2,903 for a two-bedroom, and $3,681 for a three-bedroom (HUD Fair Market Rents, FY 2026, effective May 21, 2026). A new, detached, never-lived-in ADU typically rents at or above those figures, because FMR is a market-wide midpoint that includes older stock. Because state law lets you build a two- or three-bedroom unit the City’s old one-bedroom cap would have blocked, the Melrose (800 sqft, two-bedroom) and the Lincoln (1,000 sqft, three-bedroom) open up the upper end of that range — demand helped by Biola University and the city’s spot on the Los Angeles–Orange County line.