You have the plans drawn, the contractor lined up and the budget worked out. Then a friend at the city mentions the airport overlay, and you realize nobody has checked which safety zone your lot falls in. In most California cities that question never comes up. In Monterey it can end the project outright.
Monterey allows an accessory dwelling unit (ADU) — a self-contained second home on your lot — on any parcel zoned for single-family or multifamily use, and approves qualifying units ministerially, meaning a checklist review with no hearing. But units are capped at 850 square feet for a studio or one bedroom and 1,000 square feet with more than one bedroom, and they are prohibited outright in Airport Safety Zones 1 and 6 (§ 38-112.6).
Key numbers in Monterey
| What | Monterey standard | Where it comes from |
|---|---|---|
| Maximum size, studio or one bedroom | 850 sq ft | § 38-112.6 |
| Maximum size, more than one bedroom | 1,000 sq ft | § 38-112.6 |
| Minimum size | No smaller than an efficiency unit under state health and safety law | § 38-112.6 |
| Detached unit built alongside a junior unit | Up to 800 sq ft, minimum 4-ft side and rear setbacks | § 38-112.6 |
| Expansion when converting an existing structure | Up to 150 sq ft, for entry and exit only | § 38-112.6 |
| Units inside an existing apartment building | Up to 25% of existing units, or one, whichever is greater | § 38-112.6 |
| Detached units on a multifamily lot | Up to two | § 38-112.6 |
| Airport Safety Zones 1 and 6 | Prohibited | § 38-112.6 |
| Short-term rentals | Banned under 30 days, by recorded covenant | § 38-112.6 |
| Fire sprinklers | Not required unless the main home has them | § 38-112.6 |
Check the airport map first
The ordinance is a single sentence, and it is absolute:
Accessory dwelling units and junior accessory dwelling units are prohibited in Airport Safety Zones 1 and 6
Those zones come from the 2019 Monterey Airport Land Use Compatibility Plan, not from the zoning map you would normally consult, so a parcel can sit in an ordinary residential zone and still be off limits.
There is a narrower version of the same problem. Four specific parcels — Monterey County assessor numbers 013-231-027-000, 013-231-017-000, 013-231-018-000 and 013-231-028-000 — cannot get a building permit for an ADU until the owner grants the Monterey Regional Airport District an avigation easement, a recorded right for aircraft to fly over the property, or shows the parcel is no longer inside the airport's 65-, 70- and 75-decibel noise boundaries (§ 38-112.6). If your address is one of those four, budget time for it.
Monterey allows the smallest unit the law permits
Most California cities cap an ADU at 1,200 square feet, and state law lets them: a detached unit may not exceed 1,200 square feet statewide (§ 66314). Monterey does not use that room. Its caps are 850 and 1,000 square feet.
Those two figures are not arbitrary. State law forbids a city from setting a maximum below 850 square feet, or below 1,000 square feet for a unit with more than one bedroom (§ 66321. Monterey has set its ceiling exactly at the floor the state imposes on it — the smallest cap it is legally allowed to adopt. That is the practical difference between designing here and designing one town over: plan for a compact unit and a second bedroom if you want the full 1,000 square feet.
What you can build on a single-family lot
Monterey gives you three paths, and you pick one (§ 38-112.6):
One new unit, attached to the house or detached from it, meeting the city's development standards.
One conversion, inside the walls of the existing house or an existing accessory structure such as a detached garage. It needs its own exterior entrance separate from the house, side and rear setbacks sufficient for fire and safety, and any expansion beyond the existing structure is limited to 150 square feet for getting in and out.
One unit plus one junior unit. A junior ADU is a small unit carved out inside the walls of the house itself, capped statewide at 500 square feet (§ 66313). To combine the two, the full-size unit must be new detached construction of 800 square feet or less with at least 4-foot side and rear setbacks, or else a conversion of the kind above.
State law guarantees that same 800-square-foot, 4-foot-setback unit everywhere, and bars a city from adding any objective standard to it that the statute does not authorize (§ 66323.
Legalizing a unit that was never permitted
This is where Monterey is unusually generous, and it is worth reading closely if you bought a house with a finished garage or a back cottage of uncertain history.
The city will permit a nonconforming ADU — one in a structure that breaks current zoning or building rules — if creating the unit does not expand the nonconformity or the code violations, and the nonconformity does not threaten public health and safety. Separately, an unpermitted unit built before January 1, 2018 can be approved even if it does not conform to local zoning or building code requirements (§ 38-112.6).
The limits are real, though. The city can still deny that application if the building is substandard under state health and safety law, or if the building official finds in writing that fixing the violation is necessary to protect the health and safety of the public or the occupants.
State law points the same way for everyone: a city cannot deny an ADU permit over nonconforming zoning conditions, building code violations or unpermitted structures that do not threaten health and safety and are not affected by the new construction (§ 66322), and cannot require you to correct them as a condition of ministerial approval (§ 66323).
The covenant you sign before the permit
Before Monterey issues a building permit, you record a covenant drafted by the City Attorney that runs with the land. It commits you to two things: the unit will not be sold separately from the main home, and neither the unit nor a junior unit will be used for short-term rentals of under 30 consecutive days. A copy goes to the Building Division before the permit issues (§ 38-112.6).
One narrow exception exists to the no-separate-sale half: a home and ADU developed by a qualified nonprofit may be conveyed through a tenancy-in-common agreement under state law, if both the development and the transaction qualify.
Two other things the city cannot do to you. Fire sprinklers are not required in the unit unless the main home already has them, and building one does not trigger sprinklers in the existing house — the same rule state law applies statewide (§ 66314). And a conforming unit is not treated as exceeding the density allowed on your parcel; it counts as a residential use consistent with the general plan and zoning.
What this page does not cover
Monterey's own setback, height and parking standards sit in the later subsections of § 38-112.6, beyond the floor-area rules quoted here — read them in full before you design. What state law fixes regardless is the floor beneath them: a city may not block a unit of at least 800 square feet with 4-foot side and rear setbacks, and may not cap a detached unit's height below 16 feet, or below 18 feet within a half-mile walking distance of a major transit stop or high-quality transit corridor (§ 66321). Your underlying zoning district and any overlay still apply on top. Start from the Monterey code overview, and confirm your airport safety zone before anything else.
Sources
- Monterey City Code § 38-112.6 — Accessory dwelling units and junior accessory dwelling units
- California Government Code § 66313 — Definitions
- California Government Code § 66314 — Local ADU ordinances
- California Government Code § 66321 — Size and height limits a city may not impose
- California Government Code § 66322 — Parking exemptions and nonconforming conditions
- California Government Code § 66323 — Units a city must approve ministerially
