Building an ADU in Arcadia. Rules, costs, timeline.

Can I build an ADU in Arcadia?

Five things to know before you start

If you read nothing else here, read these. They are the five points that change the most projects in this city.

How many units your lot can take

Everything in this section is grounded in Arcadia Development Code § 9102.01.080 and the Government Code it implements; we won’t re-cite the local section on every line. Assume it under each heading unless we say otherwise.

On a single-family lot the ordinance allows a conversion ADU plus a junior ADU under subsection (D)(1)(A), and separately one new detached ADU of up to 800 square feet — the ordinance’s own words are “in addition to any JADU” — under (D)(1)(B). Combined, that is up to two ADUs plus a junior unit, and both routes need only a building permit. It is the same stack Gov. Code § 66323(a)(1)–(2) requires of every city. If anyone tells you the ceiling here is “one ADU plus one JADU,” the worked example in the HCD ADU Handbook (March 2026), p. 17 is the reference point.

Apartment properties work differently. On a lot with an existing multifamily building you may convert space that is not livable — storage rooms, boiler rooms, passageways, attics, basements, garages — into at least one ADU and up to 25% of the existing unit count (Gov. Code § 66323(a)(3)(B)). Detached units are allowed up to eight, never exceeding the number of existing units (Gov. Code § 66323(a)(4)(A)(ii)). With a proposed multifamily building the detached limit is two. Junior ADUs are a single-family product only (Gov. Code § 66333(a)).

Owner-occupancy

You do not have to live on the property to build or rent an ADU in Arcadia. Subsection (E)(6)(A) states plainly that ADUs created on or after January 1, 2020 carry no owner-occupancy requirement, which is what Gov. Code § 66315 requires of every city. An investment build works here the same way a family-flex build does.

The junior ADU is where the local text sits behind the statute. Subsection (E)(6)(B) requires a natural person holding legal or equitable title to live in either the primary dwelling or the junior unit, with an exception where the property is owned entirely by a governmental agency, land trust or housing organization. That language predates AB 1154. Most cities are in the same position; almost none have amended their text yet.

What about an unpermitted unit already on the lot?

Arcadia may not deny an ADU or junior ADU application because of a nonconforming zoning condition, a building-code violation or an unpermitted structure elsewhere on the lot. The condition has to be one that does not threaten public health and safety, and that the new construction does not touch (subsection (H)(1)).

A unit built before January 1, 2020 gets more protection still. The City may not refuse a permit to legalize it on the ground that it violates building standards, or that it does not comply with ADU law. The narrow exception is a finding under Health and Safety Code § 17920.3 (subsection (H)(2); Gov. Code § 66311.7, added by AB 2533).

What an ADU costs in Arcadia (2026)

Our Signature plans are fixed-price — architectural design and full permit processing included, the same number whether the lot is in Arcadia, Pasadena or the Westside. Construction is separate: once your plans are permitted, you build it yourself, bring your own licensed contractor, or build with one of our vetted construction partners. The figures below are the estimated cost to build each model with an independent licensed general contractor.

The two-story models are shown for reference. On an Arcadia lot the detached envelope is single story, so the Lincoln at 1,000 sqft is the largest plan that permits as drawn — and it lands exactly on the city’s 1,000 square-foot ceiling for a two-bedroom-plus unit. Custom work is priced per project, $9,990–$19,990 for design and permit processing.

City fees and pass-throughs

The dollar figures come from the City’s Planning Fees schedule adopted by Resolution No. 7684, effective July 1, 2026, and both include a 5% General Plan update surcharge. Two things worth knowing. A unit on the by-right building-permit track under (D)(1) does not need an ADU permit at all, so the $775 does not apply to it. And a converted ADU on a single-family lot generally needs no new utility connection, connection fee or capacity charge (§ (G)(2)(B)).

What it returns: renting your ADU

Long-term rental only, at 31 days or more. For a rent benchmark, the government figure is HUD’s Fair Market Rent for the Los Angeles–Long Beach–Glendale HUD Metro FMR Area, which covers Arcadia. For FY 2026, as revised effective May 21, 2026: $2,079 for a studio, $2,328 for a one-bedroom, $2,903 for a two-bedroom, and $3,681 for a three-bedroom. Those are metro-wide figures spanning the full range of housing stock and unit ages, so treat them as a floor rather than a forecast — a newly built detached ADU generally rents above FMR. A local property manager can price your specific street.

A newly constructed ADU first occupied after February 1, 1995 is generally outside California’s local rent-ceiling controls under the Costa-Hawkins Rental Housing Act (Civ. Code § 1954.50 et seq.). The statewide rent-cap framework under AB 1482 (Civ. Code § 1947.12) may still apply depending on the ADU’s structure and ownership. Confirm both with a landlord-tenant attorney before you write the lease.

HUD FMR figures: FY 2026 Fair Market Rents, Los Angeles–Long Beach–Glendale HUD Metro FMR Area, as revised effective May 21, 2026 (91 FR 21301). Your ADU’s actual performance depends on finish level, lot, access, parking and the rental market at the time you lease it. For payback math keyed to your lot, use the ADU ROI calculator or the ADU calculator.

When an ADU isn’t the right move

Not every Arcadia property is a good ADU candidate, and it is cheaper to learn that now than after you have paid for plans. Four situations where we would tell you to wait, pick a different unit type, or not build:

• Your numbers depend on short-term rental income. They will not work. The ordinance sets a 28-day floor and state law requires a term longer than 30 days on the units it reaches. Run the math on a 31-day-plus tenancy or reconsider.
• You want a separate-sale exit. Arcadia has not opted into AB 1033, so the ADU cannot be sold apart from the house. If a condominium-style exit is the plan, this is the wrong jurisdiction for it.
• Your lot already carries two detached accessory structures. Section 9102.01.060(A)(2) reduces the two-structure maximum by the number of legal ADUs. Something has to come down, or the ADU has to go inside the existing house. Settle that before you commission a site plan.
• You need two stories of detached space exactly as our stock plans draw it. The detached envelope is 16 feet, or 18 near qualifying transit. The honest routes are a single-story plan, a modified two-story plan, or a custom design — not a variance, which takes the project out of ministerial review entirely.

The rules that make Arcadia different

Objective design standards, written down

Most cities leave ADU appearance to a sentence or two. Arcadia lists it. Subsection (F)(8) sets out a full set of architectural requirements for any ADU on the ADU-permit track, and the word that matters is objective: these are measurable requirements a plan checker confirms, not a design board’s opinion. Review stays ministerial under Gov. Code § 66317. The standards shape the drawing; they do not open a discretionary hearing.

• Lighting. Exterior lighting is limited to down-lights, except where the building or fire code requires otherwise.
• Entrance and entry porch. The ADU needs its own exterior entrance, separate from the house’s. On an attached unit that entrance must not be visible from the public right-of-way. An attached porch or covered entry is allowed up to 60 square feet and no more than six feet deep.
• High windows. Any window nine feet or more above the finished floor must be a clerestory in frosted or obscure glass, with no dormers — a privacy rule aimed at the neighbors.
• Form and access. No mezzanine, loft or partial floor. The ADU shares the primary home’s driveway unless the Fire Department requires otherwise. Address numbers at least four inches high, visible from the street, shown on the curb next to the primary address.

The historic-siting rule

Subsection (F)(9) requires an ADU on a property listed in the California Register of Historic Resources to be located so that it is not visible from any public right-of-way. In practice that usually means tucking the unit behind the main house, which is where a backyard ADU naturally goes anyway. Arcadia has no city-wide historic ADU overlay beyond this; the rule reaches listed properties specifically. Like the design standards above it, (F)(9) sits inside subsection (F), which by its own preamble reaches only the ADU-permit track — but it is drafted in universal terms. If you are on the by-right track and your property is listed, ask Planning which reading they apply before you fix a location in the yard.

There is a second, more widely useful historic provision. A property inside an architecturally and historically significant historic district is exempt from the ADU parking requirement altogether (§ (F)(7)(B)(2); Gov. Code § 66322). Confirm your parcel’s status with the Planning Division before you assume either rule applies to you — listing and district membership are different questions with different answers.

The City’s pre-approved ADU plans

Under AB 1332 (Gov. Code § 65852.27) every California city was required to run a pre-approved ADU plan program by January 1, 2025. Arcadia actually runs one — the PAADU program — which is less common than it should be. It covers detached, new-construction ADUs only, and the eligible plans are ones the City itself already approved after January 1, 2023 under its current objective design standards. Designers submit their approved sets; the City lists the ones it accepts, with the designer’s contact details, and homeowners contract directly with that designer to use the plan.

For a homeowner the advantages are concrete. First, no Planning review. The City publishes that saving as $696; the fee schedule effective July 1, 2026 sets the ADU permit at $775, so read $696 as the City’s own figure rather than today’s arithmetic. Second, expedited plan check in the Building Division. Third, a shorter statutory clock: Gov. Code § 65852.27(b) requires a local agency to approve or deny a detached-ADU application within 30 days of a complete submittal where the application uses a plan the agency pre-approved within the current triennial California Building Standards Code rulemaking cycle, or a plan identical to one the agency already approved in that cycle. That is half the ordinary 60-day ADU clock, and it is a right most applicants never invoke. As of this review the City lists one pre-approved plan — PAADU 26-0178, a 1,000 square-foot two-bedroom, two-bathroom unit with central split air conditioning and a 50-gallon heat-pump water heater.

The 28-day rental floor, and why 31 is the real number

Subsection (E)(4) bars renting an ADU or junior ADU for a term shorter than 28 days, and says so regardless of when the unit was created. That rules out nightly and weekly stays. But 28 is not the operative floor on every unit, and this is the one place where Arcadia’s text is more permissive than the statute rather than less.

Separate sale: two statutes, and only one of them is open

Subsection (E)(5) permits an ADU or junior ADU to be rented, but bars selling or conveying it separately from the lot and the primary dwelling, except as Gov. Code § 66341 provides. That carve-out is worth reading carefully, because it is not the statute most people mean.

• Gov. Code § 66341 is a narrow statewide pathway, and it is mandatory — no local opt-in is needed, which is why Arcadia’s own text carves it out. It applies only where the ADU or the primary dwelling was built or developed by a qualified nonprofit corporation and is sold to a qualified low- or moderate-income buyer under a recorded tenancy-in-common agreement. It is a below-market-housing tool, not a route for an ordinary homeowner.
• Gov. Code § 66342 is the condominium route people usually mean by “AB 1033.” It says a city may adopt a local ordinance permitting the house and the ADU to be conveyed separately as condominiums. Arcadia has not adopted one, so that exit is closed here. Among LA-area cities only a handful have — Santa Monica (SMMC § 9.31.026) and Culver City (CCMC § 17.400.096) among them.

A junior ADU carries a recorded deed restriction saying the same thing, binding future owners (§ (E)(7)). For practical purposes: build here for rental income, family housing, or long-term value in the primary asset.