ADU rules in Lake Forest

Detached ADUs are allowed in two tracks. A Class 1 detached unit (Gov. Code 66323) of up to 800 sq ft of livable space with 4 ft side and rear setbacks is approved ministerially on a lot with a proposed or existing single-family home in any residential or mixed-use zone and may be combined with one conversion ADU and one JADU; lots with multifamily buildings may add up to two detached ADUs (proposed multifamily) or up to eight, never more than the number of existing units (existing multifamily). Larger detached units, up to 850 or 1,000 sq ft by bedroom count, are Class 2 units under the local standards in § 9.146.050(G) and may be built on any lot zoned for single-family or multifamily residential use; the city guide allows one JADU, one conversion ADU and one new attached or detached ADU together on a single-family lot. The R1, RS, RP and Portola Bluff district lists name ADUs as accessory uses, the R2 and R4 lists and the mixed-use matrix omit them, but § 9.146.050(F)(1) and state law control. No ADU or JADU may be created on a parcel from a Gov. Code 66499.41 small-lot subdivision (§ 9.146.050(K)).

Attached additions, conversions of space inside a proposed or existing home or accessory structure, and JADUs are all allowed. A conversion ADU (plus up to 150 sq ft of expansion for ingress and egress when converting an accessory structure) and a JADU are Class 1 units approved under Gov. Code 66323(a)(1) on a single-family lot, and on multifamily lots at least one ADU, and up to 25 percent of the existing unit count, may be carved out of non-livable space such as storage rooms, attics, basements or garages. A new attached addition is a Class 2 unit subject to the § 9.146.050(G) size, 25 ft front setback, 4 ft side and rear setback and 10 ft minimum interior dimension rules, with its own exterior entrance. A JADU of up to 500 sq ft must sit entirely within a proposed or existing single-family structure (an attached garage counts), with an efficiency kitchen and either its own bathroom or an interior connection to the home; the code confines JADUs to lots zoned for single-family residences.

Class 2 ADUs, attached or detached, are capped at 850 sq ft of interior livable space for a studio or one-bedroom unit and 1,000 sq ft for two or more bedrooms, and an attached Class 2 ADU on a lot with an existing home is further limited to 50 percent of that home's floor area, but neither the percentage nor the 25 ft front setback may push a unit below 800 sq ft (a 1,300 sq ft house still gets an 800 sq ft attached ADU). A Class 1 detached unit is limited to 800 sq ft of livable space, so 800 sq ft is the dividing line between the tracks: the city guide treats any detached ADU of 800 sq ft or less as Class 1 and anything larger, up to the 850 or 1,000 sq ft cap, as Class 2. Conversions of existing space have no cap beyond the existing walls plus up to 150 sq ft for access in an accessory structure, and JADUs are capped at 500 sq ft. Detached ADUs may be 16 ft tall, or 18 ft within half a mile walking distance of a major transit stop or high-quality transit corridor (plus 2 ft to match the main roof pitch) or on a lot with a multistory multifamily building; attached ADUs may reach 25 ft or the zone's height limit, whichever is lower, and two stories.

No owner-occupancy requirement applies to any ADU: § 9.146.050(F)(7)(a) says ADUs 'are not subject to an owner-occupancy requirement', matching Gov. Code 66315. For a JADU an owner must live in the main home or the JADU only when the JADU shares sanitation facilities with the main home; the requirement falls away when the JADU has its own bathroom or the property is owned by a governmental agency, land trust or housing organization, the Gov. Code 66333(b) rule since AB 1154 took effect on 1-1-2026 (Ords. 383 and 384 wrote the exception in). A JADU still needs a recorded deed restriction (no separate sale, approved size and attributes) before its certificate of occupancy. The city's March 2026 ADU FAQ and its July 2022 JADU deed-restriction template still say every JADU requires owner occupancy; the code, not those documents, governs.

Only Class 2 ADUs carry a parking requirement: one off-street space for each ADU or bedroom, whichever is less, which may sit in a setback area or in tandem on the shared driveway (widened up to 30 ft or 60 percent of the lot width, whichever is greater). No space is required where the ADU is within half a mile walking distance of public transit (defined to include any bus stop), in an architecturally and historically significant historic district, part of the proposed or existing home or an accessory structure, where on-street permits are required but not offered, within one block of an established car-share stop, or filed together with a new home that meets one of those criteria, the six exemptions of Gov. Code 66322(a); Class 2 applicants show the walking distance to the nearest transit stop on their plans. Class 1 detached units, conversions and JADUs need no parking, and garages, carports or spaces demolished or converted for an ADU need not be replaced. On a plain reading of the per-bedroom wording, which mirrors Gov. Code 66314(d)(10)(A), a Class 2 studio needs no space.

Every ADU and JADU needs a ministerial ADU permit from the Planning Division plus a building permit (Ord. 384 ended the earlier split under which conversions needed only a building permit); the 2026 ADU permit application fee is $687, a separate street address must be assigned first, and applications are filed in person at City Hall. The city must rule on completeness within 15 business days and approve or deny a complete application within 60 days without discretionary review or a hearing, or it is deemed approved; incompleteness findings and denials may be appealed in writing to the Planning Commission, which decides within 60 business days. A design that misses the objective standards may instead seek a discretionary use permit under Chapter 9.184 (§ 9.146.050(J)), an optional path rather than the normal route.

An ADU or JADU may be rented, but § 9.146.050(F)(4) bars any rental term shorter than 30 days however old the unit is, and (F)(5) bars selling or conveying it apart from the lot and primary dwelling except through a qualified nonprofit under Gov. Code 66341; the code has no Gov. Code 66342 condominium opt-in. Separately, the 2017 zoning amendment the city calls its Short-Term Rental Ordinance (Ord. 297, which rewrote § 9.04.030 and every residential district's use lists) defines 'Short Term' as 30 or fewer days and a short-term rental as a transitory-lodging use, which every residential district and every planned community lists as prohibited; the only exception is a limited home rental, the rental of a person's entire domicile up to three times a year for under 30 days, registered and taxed, which cannot be an ADU because of (F)(4). The city's STR page calls STRs a prohibited use in all residential areas, a misdemeanor with fines up to $1,000 per violation, and the city ADU guide says ADUs and JADUs may not be used as short-term rentals. Read together, rentals longer than 30 days are the safe term; the city says long-term rentals need no city approval.