Montclair ADU rules

Maximum size

A Class 2 (City standard) ADU, attached or detached, may have up to 850 sq ft of interior livable space for a studio or one bedroom and 1,000 sq ft for two or more bedrooms. An attached ADU on a lot with an existing home is also limited to 50% of the main home's floor area. Lot coverage (35%), open space and front setback limits apply, but none of these or the 50% limit can hold an ADU below 800 sq ft. A new detached ADU of up to 800 sq ft with 4 ft side and rear setbacks is allowed as a Class 1 ADU.

Source: Montclair Ordinance No. 25-1014, Exhibit A (Chapter 11.23 Accessory Dwelling Units), City Council agenda packet of January 20, 2026, §§ 11.23.050(A)(2), 11.23.070(A), (C), accessed 2026-11-02.

Setbacks

New ADUs need 4 ft side and rear setbacks. A Class 2 ADU also needs a 25 ft front setback (30 ft for a second story), but the front setback cannot hold an ADU below 800 sq ft. No setback is needed when an ADU is built in the same place and size as an existing structure, and converted Class 1 ADUs need only setbacks that meet fire and building codes. Class 2 ADUs must leave at least 1,000 sq ft of open outdoor space behind the front setback line, at least 15 ft wide.

Source: Montclair Ordinance No. 25-1014, Exhibit A (Chapter 11.23 Accessory Dwelling Units), City Council agenda packet of January 20, 2026, §§ 11.23.050(A)(1)(d), (A)(2)(a), 11.23.070(B), (D), accessed 2026-11-02.

Local ADU rules

Montclair's ADU and JADU rules are in Municipal Code Chapter 11.23, repealed and replaced by Ordinance 25-1014, adopted February 2, 2026 and in effect March 4, 2026. Every ADU and JADU needs a ministerial ADU permit and a building permit, with no hearing. The City says within 15 business days whether an application is complete and acts within 60 days of a complete application.

Source: City of Montclair, Adopted Ordinance No. 25-1014 (ADUs and JADUs), Notice posted February 5, 2026 (adoption and effective date); MMC §§ 11.23.040(A), (C), accessed 2026-11-02.

ADU types under state law (Class 1)

On a single-family lot: one converted ADU inside the home or an existing accessory structure (up to 150 sq ft added for entry and exit) plus one JADU, and also one new detached ADU of up to 800 sq ft of livable space with 4 ft side and rear setbacks. On a multifamily lot: converted ADUs in non-living space (at least one, up to 25% of existing units), plus detached ADUs with 4 ft side and rear setbacks (up to 8 on a lot with existing multifamily, not more than the number of existing units; up to 2 with proposed multifamily). All other ADUs are Class 2 and follow the City's own standards.

Source: Montclair Ordinance No. 25-1014, Exhibit A (Chapter 11.23 Accessory Dwelling Units), City Council agenda packet of January 20, 2026, § 11.23.050(A)-(B), accessed 2026-11-02.

Height

A detached ADU may be 16 ft. It may be 18 ft within a half mile walk of a major transit stop or high-quality transit corridor (plus 2 ft, up to 20 ft, to match the main home's roof pitch), or on a lot with a multifamily building of more than one story. An attached ADU may be 25 ft or the zone's limit for the main home, whichever is lower, and no more than two stories. Class 2 detached ADUs are limited to one story. Height is measured from existing grade or the lowest floor, whichever is lower, to the peak.

Source: Montclair Ordinance No. 25-1014, Exhibit A (Chapter 11.23 Accessory Dwelling Units), City Council agenda packet of January 20, 2026, §§ 11.23.060(B), 11.23.070(I), accessed 2026-11-02.

Parking

A Class 2 ADU needs one off-street space per unit or per bedroom, whichever is less, which may be in setback areas or tandem. No space is needed within a half mile walk of public transit, in a historic district, for an ADU inside the home or an accessory structure, where on-street permits are required but not offered, within one block of a car share stop, or when the ADU is filed with a new home or multifamily building and meets one of these tests. Garage, carport or uncovered spaces removed for an ADU need not be replaced.

Source: Montclair Ordinance No. 25-1014, Exhibit A (Chapter 11.23 Accessory Dwelling Units), City Council agenda packet of January 20, 2026, § 11.23.070(F), accessed 2026-11-02.

Design, privacy and landscaping (Class 2 ADUs)

Class 2 ADUs must use the same wall, roof, window and door materials and colors as the main home and match its dominant roof slope, have down-lighting, have their own entrance facing a different direction from the main home's entrance, and be at least 10 ft wide inside with 7 ft walls. Windows and doors may not look directly onto a neighboring home's lot unless screened, and those less than 30 ft from a side or rear lot line must be clerestory or frosted. Second-story walls must step back at least 5 ft from the ground-floor walls. Evergreen screening plants (or a 6 ft solid fence) are required between the ADU and any public street.

Source: Montclair Ordinance No. 25-1014, Exhibit A (Chapter 11.23 Accessory Dwelling Units), City Council agenda packet of January 20, 2026, § 11.23.070(G)-(H), accessed 2026-11-02.

Junior ADUs

A JADU may have up to 500 sq ft of interior livable space inside a single-family home (an attached garage counts), with an efficiency kitchen; if it shares a bathroom with the home, it needs an inside door to the home and its own outside entrance. JADUs are allowed only on lots zoned for single-family homes. An owner must live on the lot only when the JADU shares a bathroom with the home. A recorded deed restriction says the JADU cannot be sold separately and stays the size allowed.

Source: Montclair Ordinance No. 25-1014, Exhibit A (Chapter 11.23 Accessory Dwelling Units), City Council agenda packet of January 20, 2026, §§ 11.23.030(E), 11.23.060(A)(3), (G)(2), (H), accessed 2026-11-02.

Fees, utilities, sprinklers and rentals

No impact fees for a JADU or an ADU under 750 sq ft of interior livable space; larger ADUs pay in proportion to the main home's size. A school district clearance letter is required. JADUs and converted ADUs on a single-family lot need no new utility connection or connection fee unless built with a new home; other ADUs need a separate connection, with a fee in proportion to their size or plumbing fixtures. Fire sprinklers are needed only if the main home needs them. No ADU or JADU may be rented for less than 30 days or sold separately.

Source: Montclair Ordinance No. 25-1014, Exhibit A (Chapter 11.23 Accessory Dwelling Units), City Council agenda packet of January 20, 2026, §§ 11.23.060(C)-(E), 11.23.080, accessed 2026-11-02.

Septic systems

An ADU or JADU that will connect to a septic system needs a percolation test from the last 5 years (10 years if the test was renewed).

Source: Montclair Ordinance No. 25-1014, Exhibit A (Chapter 11.23 Accessory Dwelling Units), City Council agenda packet of January 20, 2026, § 11.23.060(F), accessed 2026-11-02.