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

What you can build in Duarte

Everything in this section is grounded in DDC § 19.60.160 and Gov. Code §§ 66310–66342, with state-law citations called out on their own where they preempt or supplement the local rule. We won’t re-cite the Duarte ordinance section on every line below — assume it under each subsection unless we say otherwise.

Number of units allowed

Per DDC § 19.60.160(C):

• Single-family lots: one detached, attached, or converted ADU, plus one JADU. The ordinance also allows a JADU together with a detached or converted ADU where they meet the requirements of Government Code § 65852.2(e) — the old-numbering citation for what is now the § 66323 framework. Current state law is more generous than this reading — see the state-law section below.
• Multifamily lots: up to two detached ADUs, plus conversion ADUs within the multifamily structure limited to 25% of existing dwelling units (minimum one), in non-living-space portions of the building. Note: California SB 1211 (2024) raised the state-law detached-ADU floor to eight on multifamily lots — see the state-law section below.

Size limits

Per DDC § 19.60.160(F)(1)–(2):

• Studio or one-bedroom ADU: up to 850 sqft.
• ADU with two or more bedrooms: up to 1,000 sqft.
• Minimum ADU size: 150 sqft.
• Attached ADU: up to 50% of the primary dwelling’s floor area, but never reduced below 800 sqft regardless of how small the primary home is.
• Junior ADUs: 150–500 sqft, per DDC § 19.60.160(B).

Statewide Exemption ADU floor: per Gov. Code § 66323, every eligible lot is entitled to at least one ADU of up to 800 sqft, 16 ft in height, with 4-ft side and rear setbacks, regardless of local development standards — as long as the unit meets building code and health/safety requirements.

Setbacks

Duarte’s ADU ordinance, as adopted, does not carve out a distinct side or rear setback standard for ADUs separate from the base residential zone. In that silence, the state-law floor controls: no more than 4 feet side and rear setback may be required for a conforming ADU (Gov. Code § 66314(d)(7)). Front setbacks follow the base zone’s standard and cannot be applied to block an 800-sqft ADU (Gov. Code § 66321(b)(3)). Converting an existing structure into an ADU in the same footprint does not trigger a new setback requirement.

Maximum height

This is Duarte’s defining constraint. Per DDC § 19.60.160(F)(3)–(4):

• Detached ADU — default: maximum 16 feet and one story.
• Two-story exception: a detached ADU may exceed 16 feet only when built above an existing or proposed detached garage. The ground floor must remain dedicated off-street parking for two or more vehicles, and the second-floor ADU footprint cannot exceed the garage footprint below it.
• Attached ADU: cannot exceed the height or number of stories of the existing primary dwelling.

What this means for design: Duarte is, by default, a 1-story detached-ADU market. Our two-story Signature Homes are detached-only products designed for roughly 22 to 25 feet of envelope — they don’t fit Duarte’s 16-ft standard lot, and we don’t offer them as an above-garage custom structure at this time. For the large majority of Duarte homeowners, a 1-story detached Signature Home is the direct, permit-ready path. More on this in “Building within the 16-foot height cap” below.

Parking

Per DDC § 19.60.160(F)(12)–(14):

• Default rule: one off-street parking space per ADU.
• Waived when the lot qualifies for any of five triggers — matching the statewide exemption framework in Gov. Code § 66322:
  • Within ½ mile walking distance of public transit.
  • Within a proposed or existing primary dwelling, or an existing structure.
  • Within a historic district.
  • On a lot where on-street parking permits are required but not offered to the ADU occupant.
  • Within one block of a car-share vehicle.
• Garage or carport conversion/demolition: no replacement parking is required for the primary dwelling while the ADU remains in use.
• Dimensions: required spaces must be at least 20 feet long and may be uncovered.

Lot coverage and FAR

Per DDC § 19.60.160(F)(5), lot coverage limits may be exceeded for an ADU up to 800 sqft. An ADU larger than 800 sqft must meet the base zone’s lot coverage, landscape, hardscape, and other local development standards.

Owner-occupancy

DDC § 19.60.160(D)(2)(e) states plainly: “Owner-occupancy for all ADU/JADUs shall be required after January 1, 2025.” That is a significant conflict with state law. California Gov. Code § 66315 prohibits any city from imposing an owner-occupancy requirement on an ADU — full stop, with no sunset date and no exception. A local ordinance provision that conflicts with state ADU law is null and void under Gov. Code § 66316; the city is required to apply state law until its ordinance is corrected. In practice, this means Duarte homeowners are not required to live on-site to build and rent out an ADU, notwithstanding Duarte’s own published text. Junior ADU owner-occupancy is a different, narrower question — see the JADU section below and the AB 1154 discussion in the state-law section.

Junior ADUs (JADUs)

Per DDC § 19.60.160(G):

• Size: 150–500 sqft, entirely within the walls of an existing or proposed single-family dwelling.
• Density: one JADU per single-family lot. A JADU may not connect to a detached ADU.
• Entrance: separate exterior entry required.
• Kitchen: efficiency kitchen required, per the statute governing JADU cooking facilities.
• Parking: no additional parking may be required for a JADU — unless the JADU is created from a converted attached garage, in which case Duarte’s ordinance calls for replacement off-street garage parking. This conflicts with state law: Gov. Code § 66334(a) does not allow a city to require parking for a JADU under any circumstance, including a garage-conversion JADU. The state-law rule controls.
• Owner-occupancy: the owner must occupy either the single-family dwelling or the JADU as a principal residence, unless the owner is a government agency, land trust, or housing organization. AB 1154 narrows this — see the state-law section below.

Design standards, fire, and solar

• Architectural match: new ADUs must architecturally match the primary residence, and a second-story balcony is not permitted on an above-garage ADU (DDC § 19.60.160(F)(6)).
• Soundproofing: attached ADUs require common-wall soundproofing (DDC § 19.60.160(F)(9)).
• Fire sprinklers: only required in a new ADU if the primary dwelling is already required to have them (DDC § 19.60.160(F)(10)) — matching the state-law rule in Gov. Code § 66314(d)(12).
• Solar: new detached ADUs require rooftop solar per the Building Code (DDC § 19.60.160(F)(11)).

Impact fees and permitting timeline

Duarte’s ADU ordinance text does not itemize its own impact-fee threshold. In that silence, the state-law floor applies: an ADU of 750 sqft or less is exempt from impact fees, and a larger ADU is charged fees proportional to the primary dwelling’s size (Gov. Code § 66311.5(c)(1)). Building permit and plan-check fees in Duarte are valuation-based — calculated from the fair-market value of labor and materials for your specific project rather than a flat ADU fee — so Duarte’s own Building & Safety Division is the source for your project’s exact number. Review is ministerial: the Community Development Director approves or denies a complete application without a public hearing (DDC § 19.60.160(E)), on the timeline described in “Permitting your ADU in Duarte” below.

The ADU permit process, step by step

Per DDC § 19.60.160(E) and Gov. Code § 66317, Duarte must review a complete ADU or JADU application ministerially — no public hearing, no neighbor notice, no discretionary design review. If your plans meet the objective standards in DDC § 19.60.160, the city must approve.

For a CALI ADU Signature plan, the permit step runs in weeks, not months. Here is the real start-to-finish math:

• Signature plan preparation: about 2 weeks — a pre-engineered plan customized to your lot.
• Completeness check: Duarte must determine completeness and notify you in writing within 15 business days (SB 543, eff. Jan 1, 2026; Gov. Code § 66317(a)(2)).
• Ministerial approval: up to 60 days from a complete application — deemed approved if the city misses that clock (Gov. Code § 66317). Because a Signature plan is pre-engineered, Duarte’s review is a conformance check against a plan already vetted for state and local compliance, not a from-scratch evaluation — that’s what keeps this phase in weeks rather than months.
• Construction: 4 to 6 months depending on the model — under 600 sqft runs about 4 months, 600–800 sqft about 5 months, and over 800 sqft about 6 months. This is the guaranteed phase: your construction schedule is set in writing in your contract with the independent licensed general contractor you choose to build it.
• Total, start to finish: roughly 6 to 9 months for a Signature plan, design through move-in.

A custom-designed ADU runs slower — a bespoke design adds drafting time up front, and Duarte’s Building & Safety Division is reviewing your drawings for the first time rather than confirming a plan it has already seen in a similar form. The 6–9 month figure above is for Signature plans only.

CALI ADU handles design, permitting, and construction management under one contract. You build with an independent licensed general contractor of your choice — we don’t self-perform construction as the general contractor at this time.

One Duarte-specific note worth knowing: the city runs a Pre-Approved ADU Program offering standard ADU plans already reviewed and approved by the Building and Safety Division. Using one of those plans as-is (no modifications) can shorten the design-and-permitting timeline further — ask Duarte Planning whether your lot and goals fit that program before committing to a custom design.

Renting out your new ADU

Duarte’s ordinance sets a 30-day minimum rental term for ADUs and JADUs (DDC § 19.60.160(D)(2)(c)) — matching the California state-law floor exactly (Gov. Code § 66323(e)). There is no local tightening here: a Duarte ADU is a standard long-term rental, not a nightly or weekend unit, and Duarte hasn’t layered on anything stricter than what state law already requires.

For a rent anchor, we start with the federal government’s own benchmark: HUD’s Fiscal Year 2026 Fair Market Rents for the Los Angeles-Long Beach-Glendale HUD Metro FMR Area (which includes Duarte), effective October 1, 2025, list $2,085 for a one-bedroom, $2,601 for a two-bedroom, and $3,298 for a three-bedroom unit. A newly built, privately-owned detached ADU in a well-kept San Gabriel Valley foothill neighborhood typically rents at or somewhat above these HUD figures — a private entrance, in-unit laundry, and new finishes are exactly what commands a premium over the FMR benchmark, which reflects a broad mix of housing stock across the whole HUD Metro area.

New Duarte ADUs also typically fall outside California’s statewide rent-cap law (AB 1482, Civ. Code § 1947.12), which exempts buildings under 15 years old on a rolling basis — confirm current status with a California real estate attorney before setting rent, since rules in this area change often.