Building an ADU in Monterey Park. Rules, costs, timeline.

What you can build on your lot

Everything in this section is grounded in the City of Monterey Park’s ADU Development Standards (Oct. 14, 2025), MPMC Ch. 21.50, and the state code those documents defer to, with state-law citations called out where they supply or override the rule. We won’t re-cite the City handout on every line — assume it under each heading unless we tell you otherwise.

Number of ADUs per lot

• Single-family lot. Per Gov. Code § 66323(a), you may combine a conversion ADU created from existing space, a junior ADU (≤ 500 sqft, inside the home), and a newly built detached ADU of up to 800 sqft — up to two ADUs plus a JADU. The City’s June 2025 handout describes one ADU plus one JADU; where the local summary is narrower than the state stack, state law controls (see the state-law section below).
• Multifamily lot — existing building. Up to eight detached ADUs, not to exceed the number of existing units, plus conversion ADUs in non-livable space — at least one, up to 25% of the existing units. The City’s handout already reflects the SB 1211 eight-unit allowance (Gov. Code § 66323(a)(3)–(4)).
• Multifamily lot — proposed building. Up to two detached ADUs (Gov. Code § 66323(a)(4)).

Size limits

• Detached ADU: up to 1,200 sqft — a notably generous cap that fits a full three-bedroom single-story home.
• Attached ADU: up to 50% of the primary dwelling’s floor area or 800 sqft, whichever is greater.
• Statewide-exemption ADU: an 800-sqft unit at 16 feet with 4-foot side and rear setbacks must be permitted regardless of the underlying zone’s lot coverage, floor-area ratio, or open-space limits (Gov. Code § 66321(b)(3)).
• Conversion ADU: no square-foot cap when created within existing permitted space. A garage may be converted and expanded by up to 150 sqft for ingress and egress (Gov. Code § 66323(a)(1)(A)).
• Junior ADU: up to 500 sqft inside the primary dwelling, attached garage included (Gov. Code § 66313(d)).

Setbacks and building separation

Side and rear setbacks are 4 feet for a new attached or detached ADU — matching the state-law floor in Gov. Code § 66314(d)(7). A conversion ADU keeps the existing setbacks when it is built in the same location and to the same dimensions. The City’s handout also applies building-separation standards between a detached ADU and other structures on the lot: 5 feet between habitable and non-habitable buildings, 10 feet between habitable buildings at the first floor, and 11 feet at the second floor, measured between the nearest sections of the buildings. On a typical Monterey Park lot, the practical move is to place the ADU in the rear yard — where the handout locates new attached and detached units — and let the 4-foot envelope do the work.

Maximum height — what this means for design

A detached ADU in Monterey Park is capped at 16 feet — the state floor in Gov. Code § 66321(b)(4)(A). The cap rises to 18 feet when the lot sits within a half-mile walking distance of a major transit stop or high-quality transit corridor — with 2 more feet allowed to match the primary home’s roof pitch (Gov. Code § 66321(b)(4)(B)) — and to a flat 18 feet on a lot that holds a multistory multifamily building (§ 66321(b)(4)(C)). An attached ADU may reach 25 feet as part of the primary structure (Gov. Code § 66321(b)(4)(D)). Read plainly: Monterey Park is a single-story detached-ADU market. Our two-story Signature Homes are detached-only designs that need roughly 25 feet of envelope to permit, so they sit out on Monterey Park lots. All six of our single-story models clear the 16-foot bar with conventional roof forms. The 25-foot attached envelope is not a path to a two-story product here; it applies to additions built into the primary home.

Parking

One parking space is called for per attached or detached ADU, and it can be tandem on the driveway. The requirement is waived when the ADU is within one-half mile walking distance of public transit, and the remaining state exemptions in Gov. Code § 66322(a) apply as well — a historic-district parcel, an on-street permit area where the occupant is not offered a permit, or car-share within a block. A JADU never requires parking (Gov. Code § 66334(a)), and neither does a conversion. When a garage, carport, or covered space is demolished or converted in conjunction with an ADU, those spaces never have to be replaced (Gov. Code § 66314(d)(11)) — the City’s handout states this rule in full. Much of Monterey Park’s bus-served grid along Garvey, Atlantic, and Garfield falls within the half-mile transit radius.

Lot coverage, FAR, and design criteria

The dividing line in Monterey Park is 800 sqft. An ADU of 800 sqft or smaller must comply with state requirements only — the City’s handout says outright that local planning requirements may not be imposed on it, which mirrors the statewide-exemption rule in Gov. Code §§ 66321(b)(3) and 66323(b). Above 800 sqft, the City’s design criteria at MPMC § 21.08.080(J) apply: the ADU must be architecturally compatible with the primary building in color, materials, roof type and pitch, and scale. That is a real standard, not a veto — review stays ministerial — and our Signature Homes are designed to read naturally beside the San Gabriel Valley’s Spanish, ranch, and mid-century housing stock either way.

Owner-occupancy

Monterey Park does not require the owner to live on the property for an ADU — matching Gov. Code § 66315, which bars the requirement statewide. For a junior ADU, the City requires owner-occupancy of the primary residence or the JADU only if the JADU does not have its own bathroom. That is the post-AB 1154 rule: effective January 1, 2026, AB 1154 amended Gov. Code § 66333(b) so JADU owner-occupancy applies only when the JADU shares sanitation facilities with the primary dwelling. Most cities’ published summaries still describe the broader pre-2026 rule; Monterey Park’s October 2025 handout is already current — a JADU with its own dedicated bathroom carries no owner-occupancy mandate.

Impact fees and city fees

No development impact fees may be charged on any ADU under 750 sqft, and a JADU under 500 sqft is exempt as well (Gov. Code § 66311.5(c) — the renumbered former § 66324). Above 750 sqft, MPMC § 21.50.040 charges impact fees proportionally to the primary dwelling’s square footage — the formula state law requires, not a flat per-unit charge. On the city-fee side, the FY 2025–26 Planning Fee Schedule lists planning review for a new ADU at $792.83 and the planning plan-check fee for single-family residential / ADU at $401.02; building-permit and plan-check fees are valuation-based on top. Separate utility metering is optional — if you elect it, connection fees are proportional under the same MPMC section.

Permitting timeline

ADU and JADU applications are reviewed ministerially — 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, and SB 543 (effective January 1, 2026) requires a written completeness determination within 15 business days (Gov. Code § 66317(a)(2)). The City’s process runs planning approval, then plan check, then building permit — the sequence its handout publishes for every ADU type.

How California state law overrides Monterey Park

Because MPMC Ch. 21.50 defers its dimensional standards to the Government Code, Monterey Park has fewer state-local conflicts than most cities — its October 2025 handout already tracks AB 1154, SB 1211, and the no-replacement-parking rule. But a few points still deserve the preemption flag, and under Gov. Code § 66316 the state standard controls wherever a local summary reads narrower.

• More units per single-family lot. The City’s June 2025 Number of Permitted ADUs handout shows “1 ADU & 1 JADU” for a single-family lot. State law allows more: under Gov. Code § 66323(a)(1)–(2) and the HCD ADU Handbook (March 2026, pp. 17–18), a single-family lot may combine a conversion ADU, a JADU, and a new detached ADU of up to 800 sqft — up to two ADUs plus a JADU. We submit under the state stack and document the preemption.
• The 800-sqft floor beats local coverage and design rules. An 800-sqft ADU at 16 feet with 4-foot setbacks must be approved regardless of lot-coverage, floor-area-ratio, or open-space limits (Gov. Code § 66321(b)(3)), and a § 66323 statewide-exemption unit is exempt from local development and design standards entirely (Gov. Code § 66323(b)) — so the architectural-compatibility criteria at MPMC § 21.08.080(J) cannot reach an ADU of 800 sqft or less. The City’s handout says the same.
• Attached ADUs get 25 feet by right. Whatever the underlying zone says, state law guarantees an attached ADU up to 25 feet or the zone’s primary-dwelling height limit (Gov. Code § 66321(b)(4)(D)) — the figure the City’s handout publishes.
• JADU owner-occupancy is narrower than the old rule. AB 1154 amended Gov. Code § 66333(b) effective January 1, 2026 so JADU owner-occupancy applies only when the JADU shares a bathroom with the main home. Monterey Park’s handout already states the narrowed rule — rare among LA County cities — so here the flag is confirmation, not conflict.
• Garage-conversion replacement parking is barred. Gov. Code § 66314(d)(11) prohibits requiring replacement parking when a garage is demolished or converted for an ADU. The City’s handout reflects this in full.

Renting an ADU in the San Gabriel Valley

Plan a Monterey Park ADU around 30-day-or-longer tenancy. The City prohibits short-term rental of an ADU or JADU outright, and MPMC § 21.50.020 records a covenant at planning clearance limiting ADU rentals to 30 days or longer — the term state law lets a city require (Gov. Code § 66323(e); § 66333(g) for JADUs). The compliant income model is a long-term residential lease or a furnished mid-term rental — corporate, traveling-medical, or academic tenants.

The benchmark worth anchoring to: HUD’s Fair Market Rents for the Los Angeles–Long Beach–Glendale metro area, revised effective May 21, 2026, put a one-bedroom at $2,328, a two-bedroom at $2,903, and a three-bedroom at $3,681 per month (FY 2026 FMRs, huduser.gov; 91 Fed. Reg. 21301). A newly built detached ADU with in-unit laundry and a private entrance typically rents at or above those figures, and Monterey Park’s drivers are durable: Cal State LA and East Los Angeles College a short hop away, the downtown LA job base via the I-10 and 60, and a deep multigenerational housing culture that keeps well-built backyard homes occupied — often by family rather than tenants at all.

For payback math keyed to your lot and financing assumptions, use the ADU ROI calculator.

Newly constructed ADUs first occupied after February 1, 1995 are generally exempt from California 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 before you lease.

HUD Fair Market Rents are a federal benchmark for the metro area, not a guarantee of what your unit will rent for. Actual performance depends on finish level, lot, access, parking, and the rental market when you lease.