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

Up to two ADUs plus a junior ADU. Duarte Development Code § 19.60.160.C allows one detached, attached or converted ADU on a single-family lot, one JADU, and — at C.3 — a JADU together with a detached or converted ADU where both meet the state statewide-exemption criteria. C.3 reaches the state stack, but it does so by citing a repealed section number.

The operative rule is Gov. Code § 66323(a)(1)–(2): one conversion ADU from existing space, one JADU, and one newly constructed detached ADU of up to 800 sqft, combinable on the same lot, confirmed by the HCD ADU Handbook (March 2026, p. 17). On a lot with an existing multifamily building, C.4 caps detached ADUs at two — that is preempted by Gov. Code § 66323(a)(4)(A)(ii), which allows up to eight, capped at the number of existing units. Converted ADUs in a multifamily building are limited to 25% of the existing units, minimum one, in non-living space.

Up to 850 sqft for a studio or one-bedroom and 1,000 sqft with two or more bedrooms, per Duarte Development Code § 19.60.160.F.1–F.2. The minimum is 150 sqft. An attached ADU may not exceed 50% of the primary dwelling’s floor area, but that percentage may never cut the allowance below 800 sqft. Gov. Code § 66321(b)(2) puts the same floor under it from the state side: no city may cap an ADU below 850 sqft for a studio or one-bedroom, or below 1,000 sqft with two or more bedrooms.

Size also interacts with lot coverage. Under F.5 the underlying zone’s maximum lot coverage may be exceeded for an ADU of 800 sqft or less, but an ADU over 800 sqft must meet lot coverage, minimum landscape area, maximum hardscape area and every other development standard in the Code. A JADU is capped at 500 sqft (Gov. Code § 66313(d)).

Eighteen feet for a detached ADU — and it is the height that binds, not the story count. Duarte Development Code § 19.60.160.F.4, as amended by Ordinance 916, limits a detached ADU to “a maximum height of 18 feet and one story in height”. The 18 feet is generous. It sits above the 16-ft state floor in Gov. Code § 66321(b)(4)(A), and Duarte grants it to every detached ADU with no transit test — where state law only reaches 18 feet within a half-mile of a major transit stop or high-quality transit corridor. On a qualifying transit-proximate lot, Gov. Code § 66321(b)(4)(B) supplies an additional 2 feet to match the primary dwelling’s roof pitch, which Duarte’s text does not restate but cannot refuse.

The “one story” half is a different matter. In a findings letter dated March 17, 2026, HCD found that this provision fails to comply with State ADU Law, because state law contains no limit on the number of stories and a local agency must allow at least two. So design to the 18-foot envelope, 20 feet on a transit-proximate lot, and treat what you do inside it as a design question.

An attached ADU may not exceed the height or number of stories of the existing primary dwelling, except that an attached single-story ADU may be built to 25 feet (F.3). Gov. Code § 66321(b)(4)(D) independently protects 25 feet, or the zone’s primary-dwelling height limit, for any attached ADU.

Yes — and the City’s own limit on how is contested. Duarte Development Code § 19.60.160.F.4 reads: “A detached ADU shall be limited to a maximum height of 18 feet and one story in height. Two story detached ADUs that include heights above 18 feet are allowed for existing or proposed detached garages where the first floor garage is maintained as off-street parking for two or more vehicles, and the second floor ADU is equal to or less than the footprint of the first floor garage itself.”

Read literally, that offers one two-story route and prices it at a two-car garage on the ground floor. HCD disagrees. Its findings letter of March 17, 2026 holds that this provision fails to comply with State ADU Law, because there is no limit on the number of stories in State ADU Law and a local agency must allow at least two stories. Gov. Code § 66321(b)(4) governs instead, setting 16, 18 or 20 feet for a detached ADU on stated conditions.

Two things follow. A detached two-story ADU that fits inside the 18-foot envelope should not be refused for being two stories, and keeping a garage below it is not the price of admission. And the above-garage route in F.4’s second sentence still stands on its own terms, where the ordinance states no height ceiling at all and the garage may be newly built, because the text says “existing or proposed”.

Be clear about what has happened and what has not. HCD made a formal finding, not a court ruling. The City’s written response was due April 16, 2026, no amending ordinance has appeared, and the one-story sentence is still printed in the Code. Bring the letter to the counter.

Yes. Duarte Development Code § 19.60.160.F.4 extends the two-story path to “existing or proposed detached garages”, so a garage that does not exist yet qualifies — you are not limited to building over the one already on the lot. The conditions travel with it: the first-floor garage must be maintained as off-street parking for two or more vehicles, and the second-floor ADU must be equal to or less than the footprint of the garage below. After HCD’s March 2026 findings letter this is no longer the only way to reach a second story in Duarte, but it is still the one place the ordinance itself sets no height ceiling, and it is the cleanest thing to file.

Our Garage + ADU Above plan was drawn for exactly this shape — a new two-car garage with a studio or one-bedroom apartment of roughly 440 to 500 sqft above it, permitted as a single structure, with a fixed plan fee of $12,990. Two Duarte details to design around. F.6 prohibits a second-story balcony or similar second-story open space on any ADU, and requires materials, color, style, massing and form similar to the house — HCD found both of those subjective rather than objective under Gov. Code § 66314(a)(2), so treat them as contested rather than settled. F.11 requires rooftop solar on a new detached ADU as the Building Code prescribes.

Often not. Duarte Development Code § 19.60.160.F.12 requires one off-street space per ADU in addition to the parking the primary dwelling already needs, then waives it in five situations: the lot is within a half-mile walking distance of public transit; the ADU is wholly or partly within a proposed or existing primary dwelling or other existing structure; the lot is in a historic district; on-street permits are required but not offered to the ADU occupant; or a City-approved car-share space sits within one block. That list tracks Gov. Code § 66322, but it is one short. HCD found in March 2026 that F.12 omits § 66322(a)(6), which waives parking where the ADU application is filed alongside an application for a new single-family or multifamily dwelling on the same lot.

F.13 bars replacement parking when a garage, carport or covered parking structure is converted or demolished. Gov. Code § 66314(d)(11) reaches further and covers an uncovered space too, which HCD found F.13 fails to reflect. Where a space is still required, F.14 sets a 20-foot minimum length, allows it to be uncovered, and requires the driveway serving it on a single-family lot to be paved in Portland cement concrete — and HCD found that those standards cannot be imposed on a unit approved under Gov. Code § 66323, which is the statute most Duarte backyard units are built under. A JADU never needs parking at all (Gov. Code § 66334(a)).

Not for an ADU — the local rule saying otherwise is preempted. Duarte Development Code § 19.60.160.D.2.e still reads “Owner-occupancy for all ADU/JADUs shall be required after January 1, 2025”, and Ordinance 916 did not remove it. Gov. Code § 66315 bars a city from imposing an owner-occupancy requirement on an accessory dwelling unit, with no sunset and no exception, and Gov. Code § 66316 makes a noncompliant local provision null and void until the city fixes it. You may build an ADU in Duarte and rent both the house and the ADU while living elsewhere.

JADUs are different: D.2.e and G.1 require the owner to occupy either the single-family dwelling or the JADU, waived at G.2 only for a governmental agency, land trust or housing organization owner. AB 1154 narrowed that from January 1, 2026 — Gov. Code § 66333(b) now permits a JADU owner-occupancy requirement only where the JADU shares sanitation facilities with the primary dwelling. HCD has told the City the same thing directly: its findings letter of March 17, 2026 requires Duarte to remove owner-occupancy for all ADUs and to require it for a JADU only where sanitation facilities are shared with the primary dwelling.

No. Duarte Development Code § 19.60.160.D.2.c requires a minimum rental term of 30 days, recorded in the deed restriction every ADU and JADU carries. That is not a local preference the City could drop: Gov. Code § 66323(e) requires a local agency to impose a term longer than 30 days on a § 66323 unit, and Gov. Code § 66333(g) does the same for a JADU.

Nightly and weekly letting is out for these units everywhere in California. Month-to-month leases, annual leases and furnished mid-term tenancies are all unaffected, and Duarte has not layered anything stricter on top of the state rule.

Not as a condominium. Duarte has not adopted an AB 1033 opt-in ordinance, so the condominium route at Gov. Code § 66342 is unavailable here, and the deed restriction required by Duarte Development Code § 19.60.160.D.2.b prohibits conveying the ADU or JADU separately from the primary residence.

One narrow path survives anyway. D.2.b carves out conveyances “as permitted by Government Code 65852.26” — a repealed section — and the provision that now occupies that ground is Gov. Code § 66341 (AB 587), under which a qualified nonprofit that built the unit may convey it separately to a qualified low- or moderate-income buyer under a recorded tenancy-in-common agreement. That route is mandatory statewide and needs no city opt-in. Treat § 66341 and § 66342 as two different statutes, because they are.

Signature plan fees are fixed at $7,490 to $12,990, which includes architectural design and full permit processing. Building the unit with an independent licensed general contractor is estimated at roughly $180K–$420K across the lineup, depending on size. The Garage + ADU Above plan — a new two-car garage with a studio or one-bedroom above — carries a fixed plan fee of $12,990.

City charges are separate. A conforming ADU in Duarte is a ministerial building permit, and building-permit and plan-check fees are valuation-based, so confirm the current figures with the City’s Building and Safety Division before you budget. Duarte Development Code § 19.60.160 imposes no local ADU impact-fee schedule of its own.

Not below 750 sqft. An ADU of 750 sqft or less pays no development impact fees anywhere in California (Gov. Code § 66311.5(c)(1)), and above that threshold impact fees must be proportional to the primary dwelling’s square footage rather than charged flat per unit. Duarte Development Code § 19.60.160 sets no local ADU impact-fee schedule, so the state rule is the whole rule here.

A JADU of 500 sqft or less is exempt as well, and an ADU or JADU under 500 sqft is not subject to school impact fees (Gov. Code § 66311.5, § 66311.5(c)(3)). That makes 750 sqft the single largest cost line in the ordinance: on a one-bedroom rental, the difference between 740 and 780 sqft changes the fee bill far more than it changes the product.

The City must approve or deny a complete ADU application within 60 days, and the review is ministerial — no public hearing, no neighbor notice, no discretionary design review (Gov. Code § 66317). If the City misses that clock, the application is deemed approved. It must also determine completeness and notify you in writing within 15 business days (SB 543, effective January 1, 2026; Gov. Code § 66317(a)(2)(A)).

On a pre-engineered Signature plan, expect roughly 2 weeks of plan preparation, a permit cycle measured in weeks rather than months, then 4 to 6 months of construction — about 6 to 9 months start to finish. Custom designs run longer at both ends because the City is reviewing the drawings for the first time. Build the deed restriction into the schedule: Duarte Development Code § 19.60.160.D.2 requires it to be approved by the Community Development Director and the City Attorney before the building permit issues. HCD found in March 2026 that the City cannot require that instrument for an ADU at all, but the requirement is still in the Code, so plan the calendar around it.

Yes. The City runs a Pre-Approved ADU Program, published on the Duarte Community Development pages — the local answer to the statewide pre-approval mandate of AB 1332 (Gov. Code § 65852.27), which required every city to have a program running by January 1, 2025.

A pre-approved plan is the fastest route across the counter, and it is built as filed. CALI ADU does not participate in the program: our Signature plans are individually permitted on your lot and adapted to its grade, setbacks, driveway and utility routing. If you want a standard plan built as-is on a straightforward lot, the City program is a real option worth looking at first.

On paper yes, on every ADU and every JADU — but HCD says the City cannot require one for an ADU at all. Duarte Development Code § 19.60.160.D.2 requires a deed restriction approved by the Community Development Director and the City Attorney before the building permit issues, and recorded before the certificate of occupancy. Its listed contents include the no-separate-sale covenant (D.2.b), the 30-day minimum rental term (D.2.c), the owner-occupancy clause (D.2.e) and a bar on utility services separate from the main residence (D.2.g).

HCD’s findings letter of March 17, 2026 reaches the instrument itself, not only its clauses. Gov. Code § 66315 permits no additional standards beyond those in Gov. Code § 66314, and HCD reads a deed restriction as exactly such an additional standard: lawful for a JADU, not for an ADU.

Two of the listed clauses fail on their own terms as well. Gov. Code § 66315 bars owner-occupancy on an ADU outright. The separate-utilities ban is inconsistent with Gov. Code § 66311.5, which contemplates a separate connection for a new-construction ADU subject to a proportionate connection fee and bars requiring one for a conversion ADU — though that provision reads as a power of the agency rather than an entitlement of the applicant, so do not count on a separate meter on the strength of preemption alone. What to do in practice: the section has not been amended, so budget the time for both reviews, and read the instrument before you sign it.