Accessory Structures in Downey, CA

If you live in Downey or are thinking about moving there, accessory structures are one of those things you probably won't think about until they affect you directly. Downey has 7 specific rules on the books covering different aspects of accessory structures, and some of them might surprise you.

Tiny Homes

Downey lets residents build tiny houses under Appendix BB of the 2025 California Residential Code, adopted by reference as the "Downey Building Code" in Municipal Code Section 8993. A tiny house still needs a full building permit reviewed by the Building and Safety Division and must meet the appendix's reduced ceiling-height, egress, loft and stair standards rather than standard single-family dwelling requirements.

Key details: Governing section: Downey Municipal Code § 8993. Appendix adopted: Appendix BB, Tiny Houses. Base code: 2025 California Residential Code. Adopted by: Ordinance 26-1537, 1/27/2026. Enforcing agency: Building and Safety Division.

A tiny house built or occupied without the building permit Section 8993 requires, or that departs from Appendix BB's ceiling-height, egress or stair standards without an approved alternative, is treated as a Code violation under Section 1200: a misdemeanor punishable by up to a $1,000 fine or six months in jail, or an infraction with fines from $100 up to $500 for repeat violations, and the city can red-tag or require removal of unpermitted structures.

ADU Rental Restrictions

Downey bans short-term rentals of accessory dwelling units outright: § 9414.14(c) states no ADU may be rented for a term shorter than 30 days, a rule that applies to every ADU in the city regardless of when it was built or permitted.

Key details: Minimum rental term: 30 days for any ADU. Applies to: Every ADU, regardless of construction date. Sale restriction: ADUs cannot be sold separately from lot. JADU extra rule: Recorded deed restriction bars separate sale. Enforcement: Community Development Department code enforcement.

Renting an ADU or JADU for fewer than 30 days violates § 9414.14(c) and exposes the property owner to code enforcement action by the Community Development Department, including citation and the same abatement remedies available for other zoning violations. For a JADU with a recorded deed restriction, the Community Development Director can additionally seek an injunction or abatement order under § 9414.14(f)(6) to stop the illegal short-term use.

This is not one of those rules that cities tend to ignore. Downey actively enforces its adu rental restrictions requirements.

ADU Impact Fees

Downey waives impact fees entirely for any ADU under 750 square feet, and for larger units caps the fee proportionally to the ADU's share of the primary dwelling's floor area, under Municipal Code § 9414.18(a).

Key details: Fee waiver threshold: ADUs under 750 square feet: no impact fee. Larger ADU fee basis: Prorated to ADU's share of primary dwelling area. Excludes: Water/sewer connection fees, capacity charges. New detached ADU: Requires own utility connection. City-charged utility fee cap: Cannot exceed reasonable cost of service.

This is a fee-structuring provision, not a penalty section; the City itself is bound by the proportionality cap and cannot exceed the reasonable cost of service on utility charges. An applicant who believes a fee was miscalculated or improperly charged above the statutory cap can raise the issue with the Building and Safety Division or Community Development Department during permit review before the fee is paid.

Downey is more permissive than most cities when it comes to adu impact fees. That said, there are still limits.

Garage Conversions

Downey lets homeowners convert garages and other non-livable space into ADUs under § 9414.10(a)(3): on multifamily lots, up to 25% of existing units, but at least one, can come from converting garages, storage rooms, basements, or attics, while single-family conversions run through § 9414.08.

Key details: Multifamily conversion cap: Up to 25% of existing units, min. one. Convertible spaces: Garages, storage rooms, basements, attics. Single-family path: One of two ADUs may be a conversion. Expansion allowance: Up to 150 sq ft for entrance access. Parking impact: Converted-garage ADU exempt from added space.

Converting a garage to living space without an approved ADU or JADU permit is both a zoning violation and a Building Code violation, since the work bypasses required fire, egress, and habitability inspections. The Building and Safety Division can red-tag an unpermitted conversion, require it to be restored to garage use or brought into compliance under § 9414.20, and withhold final occupancy until the structure meets Building Code standards for dwellings.

ADU Owner Occupancy

Downey does not require an owner to live on-site for a standard detached or attached ADU, but a Junior ADU is different: the property owner must occupy one of the units as a legal domicile, secured by a recorded deed restriction before the JADU can pass final inspection.

Key details: Applies to: Junior ADUs (JADUs) only, not standard ADUs. Occupancy requirement: Owner must occupy one unit as legal domicile. Exempt owners: Government agency, land trust, housing organization. Recording deadline: Before final inspection of building permit. Recording location: Los Angeles County Recorder's office.

Failure to comply with the recorded deed restriction, including a lapse in owner-occupancy, exposes the property owner to legal action by the City. The Community Development Director is authorized to seek any remedy available at law or equity, including an injunction against continued use of the JADU in violation of the restriction, or abatement of the unit as illegal. There is no fixed fine schedule in this section; enforcement runs through civil action rather than a citation.

Shed & Carport Rules

Downey lets homeowners build a one-story detached shed, playhouse or similar accessory structure without a building permit if its floor area stays at or under 120 square feet. Larger sheds need a permit, and every detached accessory building must still meet the placement rules in Municipal Code Section 9534.22.

Key details: Permit-exempt shed size: 120 sq ft max, one story. Governing setback section: DMC § 9534.22. Front-lot setback: 5 ft from front half of adjacent lot. Building separation: 10 ft (5 ft for garages). Side-street garage setback: 20 ft from street, 26 ft from alley.

Starting work on a shed over 120 square feet before pulling a permit exposes the owner to an investigation fee equal to the standard permit fee under Section 8999.36(d), on top of the permit fee itself, whether or not a permit is ultimately issued. A shed placed inside a required setback, closer than 10 feet to another building, or inside a street-side setback on a corner lot is a zoning violation the Building Official can require to be relocated or removed.

ADU Rules

Downey allows up to two ADUs plus one JADU on single-family lots in the R-1, R-2, R-3, R-3-O, and M-U zones under § 9414.06 and § 9414.08, with size capped at 850-1,000 square feet, four-foot side/rear setbacks, and a 16-foot height limit for detached units.

Key details: Allowed zones: R-1, R-2, R-3, R-3-O, M-U. Units per single-family lot: Up to two ADUs plus one JADU. Max ADU size: 850 sq ft studio, 1,000 sq ft 2+ bed. Side/rear setback: Minimum four feet. Detached height limit: 16 feet, up to 20 near transit.

Building or expanding an ADU beyond the § 9414.08 size, setback, or height standards without a permit is a zoning violation the Building and Safety Division can red-tag during inspection, and an unpermitted ADU cannot receive final occupancy sign-off. Because Downey processes ADU applications ministerially under § 9414.16, an applicant whose plans do not meet these objective standards gets a written list of deficiencies rather than automatic denial, but continued noncompliant construction can be enforced as an unpermitted structure under § 9414.20.

The Bottom Line

Downey's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming Downey is broadly strict or permissive.

This guide is based on Downey's current municipal code. Local rules can and do change, so check the individual ordinance pages for the latest details, penalties, and FAQs.