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Lake Forest ADUs

Everything about building Accessory Dwelling Units in Lake Forest, CA

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400 sqft

749 sf
1 Bed
The city government of Lake Forest has updated its local zoning codes to comply with the State ADU mandate.
The California Building Code (CBC) 2019 is adopted.

Last Updated 09/21/21


City Hint: The City of Lake Forest permitted a total of 7 ADU projects in the past year of 2020.

Number of ADUs allowed:

Converted on Single-family Lot - Only one ADU or JADU on a lot with a proposed or existing single-family dwelling on it, where the ADU or JADU:

Limited detached on Single Family Lot: - One, in addition to any JADU that might otherwise be established

Limited Detached on Multifamily Lot
- No more than two detached ADUs on a lot that has an existing multifamily dwelling.

Converted on Multifamily Lot: At least one converted ADU is allowed on a lot within an existing multi-family dwelling, up to a number
equal to 25% of the existing multi-family dwelling units.

Types of ADUs allowed:

Detached ADU, Attached ADU, Junior ADU are permitted. ADUs may be new construction or converted from existing space. Junior Accessort Dwelling Unit (JADU)s must be converted from existing space.

Lot size:

Residential lots will not be subject to any minimum lot size for ADUs by ordinance or of the underlying zoning district. ~ Updated: State Law AB-68

ADU size:

- The maximum size of a detached or attached ADU subject to this subsection (F) is eight hundred fifty (850) square feet for a studio or one (1)-bedroom unit and one thousand (1,000) square feet for a unit with two (2) bedrooms. No more than two (2) bedrooms are allowed.
- An attached ADU that is created on a lot with an existing primary dwelling is further limited to fifty (50) percent of the floor area of the existing primary dwelling.


Converted on Single Family Lot: Has side-and rear-yard setbacks sufficient for safety, as dictated by applicable building and fire codes

Limited Detached on Single-family Lot • The side- and rear-yard setbacks are at least 4 ft;

a. No part of any ADU subject to this subsection (F) may be located within 25 ft. of the front property line;
b. No part of any ADU subject to this subsection (F) may be located within 4 ft. of a side or rear property line;
c. No setback is required for an ADU subject to this subsection (F) if the ADU is constructed in the same location and to the same
dimensions as an existing structure.


a. One off-street parking space is required for each ADU. The parking space may be provided in setback areas or as tandem parking, as defined by LFMC 9.146.050(C)(13) .
b. Exceptions. No parking required under LFMC Sec. 9.146.050 (F)(5)(a) (“Parking”) is required in the following situations:
i. The ADU is located within one-half mile walking distance of public transit, as defined in subsection Sec. 9.146.050(C)(12);
ii. The ADU is located within an architecturally and historically significant historic district;
iii. The ADU is part of the proposed or existing primary residence or an accessory structure (under LFMC Sec. 9.146.050(D)(1)(a) (“Converted on a Single-family Lot”));
iv. When on-street parking permits are required but not offered to the occupant of the ADU;
v. When there is an established car share vehicle stop located within one block of the ADU;
c. When a garage, carport, or covered parking structure is demolished in conjunction with the construction of an ADU, or converted to an ADU, those offstreet parking spaces are not required to be replaced;
d. The ADU and primary dwelling must use the same driveway to access the street;
e. Each unenclosed parking space shall be at least 9 ft. wide and 18 ft. long;
f. Each parking space that is provided in an enclosed garage shall be at least 10 ft. wide and 20 ft. long and have at least 7.5 ft. vertical clearance.

Fire Safety:

Accessory dwelling units shall not be required to provide fire sprinklers if they are not required for the primary residence and may employ alternative methods for fire protection. (State requirements)

Shape, materials and style:

a. The ADU must have an independent exterior entrance, apart from that of the primary dwelling. The ADU entrance must be located on the side or rear building façade, not facing the same public-right-of-way as the primary dwelling;
b. The interior horizontal dimensions of an ADU must be at least 10 ft. wide in every direction.


a. A single-story attached or detached ADU may not exceed 16 ft. in height above grade, measured to the peak of the structure.
b. A second-story or two-story attached ADU may not exceed the height of the primary dwelling.
c. A detached ADU may not exceed 1 story

Design review:

This Ordinance shall become effective thirty (30) days from its adoption. SECTION 6.

Number of Bedrooms:

Not specified by State Standards.


Between between 2020 and 2025, owner occupancy requirements will not apply to new ADUs. (applicable to new construction and conversion units) ~ SB-13

Utility connections:

• Converted ADUs and JADUs on a single-family lot, created under LFMC Sec. 9.146.050(D)(1)(a) , are not required to have a new or separate utility connection directly between the ADU or JADU and the utility. Nor is a connection fee or capacity charge required unless the ADU or JADU is constructed with a new single-family home.
• All ADUs and JADUs not covered by LFMC Sec. 9.146.050(G)(2)(a) above require a new, separate utility connection directly between the ADU or JADU and the utility. The connection is subject to a connection fee or capacity charge that is proportionate to the burden created by the ADU or JADU, based on either the floor area or the number of drainage-fixture units (DFU) values, as defined by the CA Plumbing Code, upon the water or sewer system. The fee or charge may not exceed the reasonable cost of providing this service

Allowed Zones:

*** Beginning in 2020, according to state law, all residential zoning districts, including single-family and multi-family, are allowed to build Accessory Dwelling Units. ***

Kitchen / Bath:

A food preparation counter or counters that total at least fifteen (15) square feet in area.

Residential Building Code:

The California Building Code (CBC) 2019 is adopted.

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