Building an ADU in Gardena. Rules, costs, timeline.

What you can build on a Gardena lot

Everything in this section is grounded in GMC Chapter 18.13 — primarily the development regulations in § 18.13.050 — with state-law citations called out where they preempt or supplement the local rule. We won’t re-cite the local section on every line; assume it under each subsection unless we tell you otherwise.

Size limits

A studio or one-bedroom ADU can be up to 850 square feet. Add a second bedroom and the cap rises to 1,000 square feet — the same caps whether the unit is attached or detached. These match the minimums state law lets any city set (Gov. Code § 66321(b)(2)). There is also a hard floor: an 800-square-foot ADU that meets the height rules and keeps 4-foot side and rear setbacks must be approved, and any development standard that would block it gets waived. Conversions of existing space have no square-footage cap at all under state law (Gov. Code § 66323(a)(1)).

Setbacks

Four feet from the side and rear property lines — the state-law floor in Gov. Code § 66314(d)(7). Convert an existing garage or other legal structure, or rebuild in the same spot at the same dimensions, and no setback applies at all. Two Gardena-specific wrinkles are worth planning around: the ADU must sit at least six feet from every other building on the lot, and it must sit behind the front-yard setback unless it replaces an existing accessory structure in its exact footprint. Both rules bend automatically if they would prevent an 800-square-foot unit. One more: nothing can encroach into a utility easement without the easement holder’s written permission — we check recorded easements on every Gardena lot before placing a unit.

Maximum height

Detached ADUs are capped at 16 feet — matching the state-law floor in Gov. Code § 66321(b)(4)(A). Lots within a half-mile walking distance of a major transit stop or high-quality transit corridor get 18 feet, plus 2 more feet to match the main house’s roof pitch (Gov. Code § 66321(b)(4)(B)) — and the same 18 feet applies on a lot with a multistory multifamily building (Gov. Code § 66321(b)(4)(C)). An ADU attached to the primary dwelling — or built above an existing garage — can reach 25 feet and two stories, though an above-garage unit requires a recorded declaration that the garage stays in use for parking.

What this means for design: Gardena is a one-story market for detached ADUs. Our two-story Signature Homes are detached-only plans that need roughly 25 feet of envelope to permit, so they sit out on Gardena lots. All six of our one-story models — from the 400-sqft Wilshire to the 1,000-sqft Lincoln — fit the 16-foot envelope without variances.

Parking

One off-street space is required only for an ADU with at least one bedroom. Studios need no parking at all — Gardena is more generous here than the state default, which lets cities require one space per unit (Gov. Code § 66322). Conversions of existing space are also exempt. The space can be tandem on your existing driveway, or in a paved setback area. Demolishing or converting a garage to build the ADU never triggers replacement parking (Gov. Code § 66314(d)(11)). And the standard state exemptions apply: within a half-mile walk of public transit, in a historically significant district, where street-parking permits exist but aren’t offered to the ADU occupant, within a block of a car-share vehicle, or when the ADU is permitted together with a new home.

Lot coverage and FAR

ADUs must respect the underlying zone’s objective standards — coverage, floor area, open space — but only up to the point where those standards would block an 800-square-foot unit. Past that point they’re waived. Two helpful companions: an ADU does not count toward the lot’s density or lot-coverage math (GMC § 18.13.040(F)), and no passageway to the street is ever required (GMC § 18.13.050(C)). On Gardena’s typical rectangular postwar lots, that combination leaves room for a detached unit on most properties.

Owner-occupancy

You do not need to live on the property to build or rent an ADU. State law flatly bars owner-occupancy conditions for ADUs (Gov. Code § 66315), and Gardena’s ordinance imposes none. Junior ADUs are different on paper: GMC § 18.13.070(H) requires a recorded deed restriction that the owner live in either the main house or the JADU. But AB 1154, effective January 1, 2026, narrowed Gov. Code § 66333(b) so owner-occupancy can be required only when the JADU shares a bathroom with the primary dwelling. A JADU with its own bathroom escapes the mandate — the ordinance text predates AB 1154, and state law preempts it.

Impact fees

ADUs of 750 square feet or less pay no development impact fees — period (Gov. Code § 66311.5; GMC § 18.13.040(E), which draws the line at exactly 750 — state law controls the boundary). Above 750 square feet, impact fees are charged proportionally to the primary home’s size, not as a flat per-unit charge. Utility connections follow a similar split: a conversion inside your existing home pays no connection fee or capacity charge, while a new detached unit needs its own utility connection — sized proportionally — and Gardena requires new utility lines to run underground (GMC § 18.13.050(I)). That last item is a real line in the budget, and it is built into every Gardena transparent estimate before you sign — see costs below.

Permitting timeline

ADU review is ministerial: no hearing, no discretionary design review, no neighbor sign-off (Gov. Code § 66317). The City must confirm your application is complete within 15 business days (SB 543, effective January 1, 2026) and approve or deny a complete application within 60 days — miss the clock and the application is deemed approved. Gardena adds a faster lane on top, covered next.

How California state law overrides Gardena

Gardena’s 2025 ordinance tracks state law more closely than most, but four points still deserve the state-law reading — because where the two differ, state law wins (Gov. Code § 66316).

• “Only one ADU” isn’t the whole story. — GMC § 18.13.040(A) opens with “only one accessory dwelling unit may be allowed per residential lot,” but the exception it references is the one that matters: under GMC § 18.13.060(A) and Gov. Code § 66323(a), a single-family lot can combine a conversion ADU carved from existing space, a junior ADU, and a new detached ADU of up to 800 square feet. The HCD ADU Handbook (March 2026, p. 17) confirms the stack — up to two ADUs plus a JADU on one ordinary lot.
• JADU owner-occupancy narrowed by AB 1154. — The deed restriction in GMC § 18.13.070(H)(4) requires owner residency for every JADU. AB 1154 (effective January 1, 2026) amended Gov. Code § 66333(b) so the requirement applies only to JADUs that share sanitation with the main house. Build the JADU with its own bathroom and the owner-residency mandate falls away.
• The 800-sqft unit is untouchable. — No lot-coverage, floor-area, open-space, or front-setback standard — local or otherwise — can stop an 800-square-foot ADU at 16 feet with 4-foot side and rear setbacks (Gov. Code § 66321(b)(3)). Gardena codifies this waiver itself, which makes the conversation at the counter short.
• The completeness clock is new. — SB 543 added a 15-business-day deadline for the City to tell you in writing whether your application is complete (Gov. Code § 66317(a)(2)). The ordinance text predates that change; the deadline applies in Gardena anyway.

Renting an ADU in the South Bay

Know the one hard rule first: GMC § 18.13.040(C) sets a minimum rental term of 31 consecutive days, and it applies to the ADU and every other residence on the lot — including your main house. There is no short-term-rental path for a Gardena ADU. This is a long-term-income play, and the math works on long-term numbers.

For a trusted benchmark, HUD’s FY 2026 Fair Market Rents for the Los Angeles–Long Beach–Glendale metro area (huduser.gov) run $1,863 for a studio, $2,085 for a one-bedroom, $2,601 for a two-bedroom, and $3,298 for a three-bedroom. A new, detached unit with in-unit laundry typically rents at or above those figures. Against a Lincoln (est. $325K–$350K to build*) generating three-bedroom rent — central to the 110, the 91, the 405, and the South Bay’s employment base — the payback period is the kind of arithmetic worth doing before the lot sits idle another year.