California ADU rules · Mono County

Can I Build an ADU in Mammoth Lakes?

Yes — you can build an ADU in Mammoth Lakes. California's statewide ADU law requires every city, including Mammoth Lakes, 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.

Figures below reflect Mammoth Lakes's adopted ADU ordinance layered on California state law.
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Can you build one?

ADUs allowed

CA state law

Yes — by right

ADUs and JADUs are allowed by right in all residential and mixed-use zones; ministerial approval, no hearing.

Cal. Gov. Code § 66317 (ministerial approval, 60-day deadline)

Units on a single-family lot

Local rule

1 detached ADU + 1 JADU + 1 interior conversion ADU (see state rules for conversions)

Allows both a detached ADU and an interior conversion ADU in addition to a JADU.

§ 17.52.055(d)(1)

Units on a multifamily lot

Local rule

up to 2 detached ADUs + conversions (1 per structure or 25% of units, whichever is greater)

Local cap of 2 detached ADUs on multifamily lots.

§ 17.52.055(d)(1)

Junior ADU (JADU)

CA state law

Allowed

Up to 500 sq ft, within the walls of an existing single-family home (single-family lots only).

Cal. Gov. Code § 66333 (junior ADUs)

Size & height

Max detached ADU size

Local rule

1,200 sq ft

Detached ADU max is 1,200 sq ft if no JADU; 800 sq ft if JADU present.

§ 17.52.055(d)(4)a

Max attached ADU size

Local rule

Greater of 50% of primary, or 850 (studio/1-bed), or 1,000 (2+ beds), not to exceed 1,200 sq ft

Local cap for attached ADUs is 1,200 sq ft.

§ 17.52.055(d)(3)b

Guaranteed minimum size

CA state law

800 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).

Cal. Gov. Code § 66321 (size minimums & height)

Max JADU size

CA state law

500 sq ft

Cal. Gov. Code § 66333 (junior ADUs)

Max height

Local rule

18 ft

Detached ADUs: 16 ft for SFR, 18 ft for multifamily or as specified; attached ADUs up to 25 ft or height of primary, whichever is less.

§ 17.52.055(d)(2)b, (d)(3)c

Setbacks

Side setback

Local rule

4 ft

4 ft minimum for ADUs up to height limits; more if exceeding height.

§ 17.52.055(d)(2)b, (d)(3)c

Rear setback

Local rule

4 ft

4 ft minimum for ADUs up to height limits; more if exceeding height.

§ 17.52.055(d)(2)b, (d)(3)c

Front setback

Local rule

No minimum front setback if it would prohibit an 800 sq ft ADU; otherwise, standard applies

§ 17.52.055(d)(2)c, (d)(3)d

Separation from main house

Local rule

None required

No specific separation required unless exceeding height/setback limits.

§ 17.52.055(d)(2)e

Parking

Parking required

Local rule

None

No parking required for ADUs.

§ 17.52.055(d)(8)a

Transit parking exemption

CA state law

Yes — 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.

Cal. Gov. Code § 66322 (ADU parking; § 66334 covers JADU parking)

Garage-conversion replacement parking

Local rule

Not required

No replacement parking required if garage/carport is converted to ADU.

§ 17.52.055(d)(8)b

Approval, timeline & cost

Approval path

CA state law

Ministerial (by right)

No public hearing or discretionary design review for a qualifying ADU.

Cal. Gov. Code § 66317 (ministerial approval, 60-day deadline)

Approval timeline

CA state law

60 days

The agency must act within 60 days of a complete application — and the ADU is deemed approved if it does not.

Cal. Gov. Code § 66317 (ministerial approval, 60-day deadline)

Owner-occupancy

Local rule

Only for a JADU

Owner-occupancy required for JADU or if both JADU and ADU are present (owner must occupy either primary or JADU).

§ 17.52.055(d)(3)b, (c)(5)d

Impact-fee waiver

CA state law

Waived 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.

Cal. Gov. Code § 66311.5 (impact fees: none for an ADU ≤ 750 sq ft or JADU ≤ 500 sq ft)

Permits required

Local rule

Building permit, Compliance with CA Building Standards Code, Compliance with Mammoth Lakes Fire Protection District Code

§ 17.52.055(d)(9)

Mammoth Lakes-specific factors that can change the answer

State law sets the floor, but these local conditions often decide whether a specific parcel works.

Very High Fire Hazard Severity Zone (VHFHSZ)

ADU not required to have sprinklers if primary dwelling does not; must comply with local fire code.

Mammoth Lakes limits detached ADUs to 1,200 sq ft unless a JADU is present, in which case the detached ADU is capped at 800 sq ft. No parking is required for ADUs, and up to two detached ADUs are allowed on multifamily lots.

Frequently asked questions

Can I build an ADU in Mammoth Lakes?

Yes. California's statewide ADU law requires Mammoth Lakes 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 Mammoth Lakes?

A detached ADU of at least 1,200 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 Mammoth Lakes?

Side and rear setbacks are limited to 4 ft. No minimum front setback if it would prohibit an 800 sq ft ADU; otherwise, standard applies.

Is parking required for an ADU in Mammoth Lakes?

None. 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 Mammoth Lakes?

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 Mammoth Lakes?

Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.

Sources

  • Mammoth Lakes Municipal Code § 17.52.055 (Ord. No. 23-03, § 4(exh. A), 4-19-2023)
  • § 17.52.055(d)(1)
  • § 17.52.055(d)(4)a
  • § 17.52.055(d)(3)b
  • § 17.52.055(d)(2)b, (d)(3)c
  • § 17.52.055(d)(2)c, (d)(3)d
  • § 17.52.055(d)(2)e
  • § 17.52.055(d)(8)a
  • § 17.52.055(d)(8)b
  • § 17.52.055(d)(3)b, (c)(5)d
  • § 17.52.055(d)(9)
  • § 17.52.055(d)(9)a
  • 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 § 66333 (junior ADUs)
  • Cal. Gov. Code § 66321 (size minimums & height)
  • Cal. Gov. Code § 66322 (ADU parking; § 66334 covers JADU parking)
  • Cal. Gov. Code § 66311.5 (impact fees: none for an ADU ≤ 750 sq ft or JADU ≤ 500 sq ft)

Last updated 2026-06-25. This is an AI-assisted summary of Mammoth Lakes'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 Mammoth Lakes Planning before relying on it.

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