California ADU rules · Siskiyou County
Can I Build an ADU in Montague?
Yes — you can build an ADU in Montague. California's statewide ADU law requires every city, including Montague, to approve a qualifying accessory dwelling unit by right, plus a junior ADU (JADU) on a single-family lot. What varies city to city are the local specifics below.
Can you build one?
ADUs allowed
CA state lawYes — by right
ADUs and JADUs are allowed by right in all residential and mixed-use zones; ministerial approval, no hearing.
Units on a single-family lot
CA state law1 ADU + 1 JADU
At least one ADU and one JADU per single-family lot (a conversion ADU may also be possible).
Units on a multifamily lot
CA state lawConversion ADUs (≥1, up to 25% of units) + up to 8 detached
Conversions of non-livable space (at least 1, or up to 25% of existing units) plus up to 8 detached ADUs on a lot with existing multifamily — never exceeding the number of existing units. JADUs are single-family only.
Junior ADU (JADU)
CA state lawAllowed
Up to 500 sq ft, within the walls of an existing single-family home (single-family lots only).
Size & height
Max detached ADU size
Local rule1,000 sq ft
Montague caps a detached ADU at 1,000 sq ft on parcels ≥ 10,000 sq ft; on smaller parcels, 850 sq ft (studio/1-bedroom) or 1,000 sq ft (2+ bedrooms). This is the city's adopted ceiling; the state by-right floor of 800 sq ft (and 850/1,000 for an attached ADU) is always protected.
Max attached ADU size
CA state law50% of the primary dwelling, but ≥850 sq ft (≥1,000 sq ft for 2+ bedrooms) is always allowed
Guaranteed minimum size
CA state law800 sq ft
An 800 sq ft ADU must be allowed regardless of FAR/lot-coverage caps; a city also cannot cap an attached ADU below 850 sq ft (1,000 for 2+ bedrooms).
Max JADU size
CA state law500 sq ft
Max height
Local rule17 ft
Montague allows a one-story detached ADU up to 17 ft and a detached two-story ADU up to 25 ft (§ 17.30.030) — above the 16-ft state baseline. The state 18-ft (transit / two-story primary) and 25-ft (attached) minimums still apply where they would give more.
Setbacks
Side setback
CA state law4 ft
A city cannot require more than 4 ft side or rear setback; conversions of existing structures are exempt.
Rear setback
CA state law4 ft
Front setback
CA state lawNo front setback may block the mandatory 800 sq ft / 16-ft / 4-ft-setback ADU; otherwise per base zone
Separation from main house
Local rule5 ft
No separation is required between a detached ADU and the main dwelling, but an ADU built ABOVE a garage may be set back no more than 5 ft from side and rear lot lines (§ 17.30.030). A garage/accessory structure permitted before 1/1/2020 and converted to an ADU needs no setback. State law sets no separation minimum.
Parking
Parking required
CA state lawUp to 1 space
At most 1 space per ADU (or per bedroom, whichever is less) — and waived in the common cases below.
Transit parking exemption
CA state lawYes — no parking required near transit & for conversions
No parking may be required within ½ mi walking distance of transit, in a historic district, for an ADU within an existing structure, within one block of car-share, or in certain permit-parking areas.
Garage-conversion replacement parking
CA state lawNot required
When a garage/carport is demolished or converted to build an ADU, replacement parking cannot be required.
Approval, timeline & cost
Approval path
Local ruleMinisterial (by right)
Ministerial: "City clerk, or designee, approval shall be required for all accessory dwelling units," based on a complete building-permit application with site plan, photos, floor area, height and setbacks. JADU permits issue within 60 days (§ 17.30.040). No hearing.
Approval timeline
CA state law60 days
The agency must act within 60 days of a complete application — and the ADU is deemed approved if it does not.
Owner-occupancy
CA state lawOnly for a JADU
No owner-occupancy requirement for ADUs (the prior sunset was removed). A JADU may require owner-occupancy, principally where it shares sanitation with the main house.
Impact-fee waiver
CA state lawWaived under 750 sq ft
An ADU of 750 sq ft or less pays no impact fees (the 750 sq ft threshold itself is exempt under § 66311.5); larger ADUs pay fees proportional to the primary dwelling. JADUs (≤ 500 sq ft) are exempt.
Permits required
CA state lawBuilding permit
Only a ministerial building permit — no conditional use permit or discretionary design review for a qualifying ADU.
Montague-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
Fire-protection alternative for under-setback ADUs
Fire sprinklers are not required in an ADU unless required for the primary residence, but for ADUs that do NOT meet setbacks the fire marshal may require other fire- and life-safety protection mechanisms (§ 17.30.030).
Setback-window design standard
Windows in a required setback that face an adjoining property must be clerestory (≥ 5'6" sill) or permanently obscured glazing, unless a different design is approved through design review at an adjoining neighbor's request (§ 17.30.030).
No short-term rentals
An ADU may be rented but not as a short-term/transient rental — the minimum tenancy is 30 days (§ 17.30.030).
Montague has a genuine local ADU ordinance (Mun. Code Ch. 17.30), not a bare deferral to state law. Distinctive Montague rules: one detached ADU may reach 17 ft (one-story) or 25 ft (two-story); a detached ADU is capped at 1,000 sq ft (850 sq ft for a studio/one-bedroom on a sub-10,000 sq ft lot); an ADU over a garage may sit within 5 ft of side/rear lines; windows in a setback must be clerestory or obscured; ADUs cannot be used as short-term rentals (30-day minimum tenancy); and approval is ministerial through the City Clerk. The ordinance also recites an "owner-occupancy after January 1, 2025" clause, but that cannot be enforced against an ADU under current state law (Gov. Code § 66315) — owner-occupancy still applies to JADUs. Verify the fire-marshal alternative-protection and design-review triggers with Montague before relying on a reduced-setback design.
Frequently asked questions
Can I build an ADU in Montague?
Yes. California's statewide ADU law requires Montague to approve a qualifying accessory dwelling unit ministerial (by right), plus a junior ADU (JADU) on a single-family lot.
How big can an ADU be in Montague?
A detached ADU of at least 1,000 sq ft must be allowed, and an ADU of 800 sq ft can never be zoned out by floor-area or lot-coverage limits. A JADU can be up to 500 sq ft.
What are the setback requirements for an ADU in Montague?
Side and rear setbacks are limited to 4 ft. No front setback may block the mandatory 800 sq ft / 16-ft / 4-ft-setback ADU; otherwise per base zone.
Is parking required for an ADU in Montague?
Up to 1 space. No parking can be required within ½ mile of transit, for conversions, or for units inside the primary home. When a garage is converted, replacement parking is not required.
How long does ADU approval take in Montague?
A complete application must be acted on within 60 days, with ministerial (by right) — no public hearing or discretionary design review for a qualifying ADU.
Do I have to live on the property to build an ADU in Montague?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Montague Mun. Code Ch. 17.30 (Accessory Dwelling Units)
- Montague Mun. Code § 17.30.030 (Accessory Dwelling Units)
- Montague Mun. Code § 17.30.030 (approval)
- Cal. Gov. Code §§ 66310–66342 (ADU Law)
- HCD 2025 Accessory Dwelling Unit Handbook
- Cal. Gov. Code § 66317 (ministerial approval, 60-day deadline)
- Cal. Gov. Code § 66323 (by-right ADU/JADU, 800 sq ft, 4-ft setbacks)
- Cal. Gov. Code § 66333 (junior ADUs)
- Cal. Gov. Code § 66321 (size minimums & height)
- Cal. Gov. Code § 66322 (ADU parking; § 66334 covers JADU parking)
- Cal. Gov. Code § 66314 (local ordinance standards)
- Cal. Gov. Code § 66315 (owner-occupancy)
- Cal. Gov. Code § 66311.5 (impact fees: none for an ADU ≤ 750 sq ft or JADU ≤ 500 sq ft)
Last updated 2026-06-28. This is an AI-assisted summary of Montague's ADU rules, drawn from its published ordinance and California ADU law — general information, not legal advice, and it may be incomplete or out of date. Verify the controlling rule for your specific parcel with Montague Planning before relying on it.
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