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

Can I build an ADU in La Mirada?

Five things to know before you start

If you read nothing else here, read these. They are the five points that change the most La Mirada projects.

How many units your lot can hold

La Mirada is a planned post-war suburb of roughly 48,000 people, mostly California Ranch houses on flat, regular tract lots. The 2025 ordinance treats those lots generously. LMMC § 21.18.060(c)(2)(A) permits one unit from each of three categories on a single-family parcel: an ADU created inside the existing house or an existing accessory structure, one newly built detached ADU, and one junior ADU inside the house. That is the same stack Gov. Code § 66323(a)(1)–(2) requires, written into the local code rather than left to preemption.

Two details are worth holding on to. A conversion of an existing accessory structure may add up to 150 square feet, but only to create a way in and out. And a parcel that has already been subdivided under both the urban lot split standards in LMMC Chapter 21.80 and the primary-and-secondary-unit standards is excluded from ADUs and JADUs (LMMC § 21.18.060(c)(2)(D)) — the SB 9 route and the ADU route are alternatives on that lot, not a stack. Confirm with Planning if your parcel has any subdivision history.

What the city cannot do

Review is ministerial. La Mirada applies objective standards to your drawings and approves the permit, or it tells you what is deficient. There is no public hearing, no public notice, and no discretionary design review (LMMC § 21.18.060(b); Gov. Code § 66317). The City may not require you to live on the property, may not demand replacement parking for a converted garage, and may not use lot coverage, floor-area ratio, open space, front setbacks or minimum lot size to stop an 800-square-foot ADU.

It also may not make you fix unrelated problems first. LMMC § 21.18.060(c)(10) says a single-family or multifamily dwelling is not required to correct legal nonconforming zoning conditions as a precondition of an ADU permit. The narrow exception is a condition the City finds necessary to protect health and safety, or a building already deemed substandard under Health and Safety Code § 17920.3.

What an ADU costs here in 2026

An ADU budget has three parts that behave very differently. The plan fee is fixed and known before you start. Construction is a range that narrows once we see your lot. City fees are mostly modest, and in La Mirada they are tied to construction valuation rather than published as a single ADU line item.

What the City of La Mirada charges

La Mirada does not publish a flat ADU-specific planning fee, and we will not invent one. An ADU is processed on the Site Plan Review and Zoning Clearance application. The Planning Division application fee schedule and the Building and Safety code fee schedules are both posted on the City’s Community Development fees page, and building fees are calculated from a building valuation table rather than a flat rate. Ask the Planning counter for a written estimate against your valuation before you set a budget.

What it returns

La Mirada sits inside the Los Angeles–Long Beach–Glendale HUD Metro Fair Market Rent Area. HUD’s revised FY 2026 Fair Market Rents for that area, published at 91 FR 21301 and effective May 21, 2026, are $2,079 for a studio, $2,328 for one bedroom, $2,903 for two bedrooms and $3,681 for three.

Read those as a floor, not a forecast. Fair Market Rents average across an entire metro and across housing of every age and condition, most of it decades older than anything you would build now. A new, permitted, detached two-bedroom unit typically rents at or above the two-bedroom figure. What it will actually fetch on your street is a question for a local agent, and worth asking before you commit.

The other half of the return is resale. A permitted ADU adds recorded square footage that comps into the sale of the property. An unpermitted conversion does the opposite: it is a disclosure problem and a financing problem, and it is why the state created a legalization path for pre-2020 units at Gov. Code § 66311.7.

When an ADU isn’t the right move

Not every La Mirada property is a good candidate, and it is cheaper to learn that now than after you have paid for drawings. Four situations where we would tell you to wait, change type, or not build:

• Your numbers depend on short-term rental income. They will not work. Neither an ADU nor a junior ADU may be rented for less than 30 days (LMMC § 21.18.060(c)(20)), and state law requires the same (Gov. Code § 66323(e)). Run the math on a month-to-month tenancy or reconsider the project.
• You need to sell the unit as its own condominium. La Mirada has not adopted an AB 1033 opt-in, which is the precondition Gov. Code § 66342 sets. Two narrower routes exist in the local code and neither is a general-purpose exit — see the separate-sale section below.
• Your parcel came out of an urban lot split. LMMC § 21.18.060(c)(2)(D) excludes a lot already subdivided under the Chapter 21.80 urban lot split standards together with the primary-and-secondary-unit standards. If you have already taken the SB 9 route on that parcel, an ADU is not the next move.
• Ten feet of separation leaves nothing worth building. After four-foot rear and side setbacks and ten feet clear of the house and garage, some La Mirada parcels cannot take a detached structure worth the money. On those lots a garage conversion or a junior ADU usually returns more than forcing a new build into the gap.

The rules that make La Mirada different

La Mirada has no Coastal Zone, no state-designated very-high fire hazard severity zone, and no historic-preservation overlay. The complications that dominate ADU projects on the Westside or in the foothills are not here. What is here is a young, permissive ordinance and a design code with teeth.

Two ADU chapters, one of them dead

Ordinance No. 736 moved accessory dwelling units into LMMC § 21.18.060 in 2025, as part of the zoning amendment implementing the City’s 6th Cycle 2021–2029 Housing Element. The section is comprehensive and current: its own purpose clause cites Gov. Code §§ 66310 through 66342, the numbering the Legislature adopted in 2024.

The older Chapter 21.54 is still printed in the published municipal code. It dates to 2008, was last touched in 2018, and still cites the repealed former Gov. Code §§ 65852.1–65852.2. It bans junior ADUs, allows one unit per lot, requires owner-occupancy and caps height at one story — none of which survives either the 2025 rewrite or state law.

The design standards, and what they actually ask for

Height, setbacks and size are what an ADU ordinance usually covers. La Mirada also adopted a full objective design standard at LMMC § 21.18.080, and § 21.18.060(c)(13) requires the design, materials, colors, architectural details and finish of an ADU to match the primary residence. Objective means the list is checkable rather than a matter of taste — which is what keeps review ministerial — but the list is long.

The provisions that most often change a drawing set: a decorative porch feature marking the primary entrance; bedrooms reached from a hallway or common area rather than through each other; four-foot paved walkways connecting the street, the entrances and the parking; at least 100 square feet of private open space per unit with a six-foot minimum dimension, outside the front and street-side setbacks; a defined base and a cornice or parapet cap achieved through at least two of four listed devices; no unbroken facade longer than 20 feet without an architectural element or a two-foot change in wall plane; and no roof line running more than 30 feet without a change.

Multifamily lots

On a lot with an existing multifamily building, LMMC § 21.18.060(c)(2)(B) allows ADUs converted from non-livable space — storage, boiler rooms, passageways, attics, basements, garages — up to 25 percent of the existing units, with at least one always allowed. Separately, LMMC § 21.18.060(c)(2)(C) allows up to eight detached ADUs on a lot with an existing multifamily dwelling, never exceeding the number of primary units on the property, at the same height ceiling and with rear and side setbacks of no more than four feet.

Both numbers match the state floor rather than falling short of it. The 25 percent conversion allowance tracks Gov. Code § 66323(a)(3)(B), and the eight-unit detached figure tracks Gov. Code § 66323(a)(4)(A)(ii), added by SB 1211 in 2025. Where an existing multifamily building already sits closer than four feet to a side or rear line, the City may not require it to be modified as a condition of approving the new unit. Junior ADUs remain single-family only.

Junior ADUs and the bathroom question

A junior ADU in La Mirada is created inside an existing or proposed single-family residence or an existing accessory structure, may not extend beyond that building’s envelope, and may add up to 150 square feet purely for a way in and out. It needs its own exterior access and its own kitchen, and it may either share the main house’s bathroom or have one of its own. Efficiency units are expressly permitted.

Separate sale — two routes, and the one the City has not taken

La Mirada bars separate conveyance of the primary dwelling and the ADU, with two exceptions written into LMMC § 21.18.060(d). The first is an ADU deed-restricted to occupancy by low- or moderate-income households for at least 45 years. The second is an ADU purchased by a qualified nonprofit — a 501(c)(3) corporation holding a welfare exemption under Revenue and Taxation Code § 214.15 for properties intended for sale to low-income families in a no-interest loan program.

That second exception is AB 587, codified at Gov. Code § 66341. It is mandatory statewide and needs no city opt-in — La Mirada has simply written it into its own code. It is a different statute from the AB 1033 condominium route at Gov. Code § 66342, which does require a city to opt in and which La Mirada has not adopted. If you are planning to sell the ADU on the open market as its own parcel, neither route gets you there.

Two parking exemptions the local list is missing

The exemption list at LMMC § 21.18.060(c)(15)(F) is generous on transit — one mile rather than the half mile state law requires — but it is short by two triggers. Gov. Code § 66322 also exempts an ADU that is part of an existing accessory structure, where the local text covers only a unit completely inside the primary residence, and an ADU in an on-street permit area where the occupant is not offered a permit. Where either applies to your lot, no parking may be required regardless of what the local list says.