Calabasas Caps How Much of Your Back Yard an ADU Can Cover

Your neighbor built a backyard cottage last spring, so you measure your own yard, sketch a 900-square-foot unit behind the pool, and take it to a designer. She asks one question you did not expect: how much of the rear yard is already covered? In Calabasas that number decides the project before setbacks or height ever come up.

Calabasas allows one accessory dwelling unit (ADU) — a self-contained second home on your lot — on any legal lot in its residential zones, up to 1,200 square feet and 16 feet tall, with 4-foot side and rear setbacks. But detached rear-yard units also face a coverage cap: structures may cover no more than 30% of the rear yard (§ 17.12.170). That cap is the one most projects hit first.

Key numbers in Calabasas

The 30% rear-yard cap, and the unit it cannot stop

The city's table is blunt about coverage:

Maximum of 30% of the rear yard area may be covered by structures, including the areas covered by the accessory dwelling unit

— § 17.12.170, Table 2-4

"Structures" is the important word. A pool house, a shed, a covered patio and the eaves of your main house all eat into the same 30%. On a modest rear yard, that arithmetic can rule out a 1,200-square-foot unit long before any setback does.

Here is the part most homeowners miss. State law limits what a city may do with coverage rules: a city cannot apply lot coverage, floor area ratio, open space or minimum lot size standards in a way that stops you building an ADU of at least 800 square feet of interior livable space with 4-foot side and rear setbacks (§ 66321). That is a ceiling on the city, not a target for you.

Calabasas has written that guarantee into its own code. Notwithstanding the table — coverage, setbacks, height and floor area alike — one ADU is allowed where the unit is 800 square feet or less, no more than 16 feet tall, and set back at least 4 feet from the rear and side lot lines (§ 17.12.170). So the practical planning question in Calabasas is rarely "can I build one?" It is "does my yard support the big one, or am I designing to 800 square feet?"

The 10-foot gap from your house

A detached unit must normally sit 10 feet from the main dwelling or any other structure. The community development director can approve less, but only for a unit that is 800 square feet or under, no taller than 16 feet, and at least 4 feet from the rear and side lines (§ 17.12.170). On a narrow lot, that separation — not the property line — is often what fixes where the unit can go.

Where the city's table is behind state law

Calabasas last amended this section in 2020, and state ADU law has moved since. Two gaps are worth knowing:

Height near transit. The city's table says 16 feet for a detached unit. State law says a city may not impose a height limit that fails to allow at least 18 feet for a detached ADU within a half-mile walking distance of a major transit stop or a high-quality transit corridor — plus 2 more feet to match the roof pitch of the main house (§ 66321. If your lot qualifies, 16 feet is not the ceiling.

Size floors. A city may not set a maximum below 850 square feet, or 1,000 square feet for a unit with more than one bedroom (§ 66321. Calabasas's attached-unit rule — the lesser of 1,200 square feet or half the main house — cannot be used to push you below that.

Neither point makes the city's table irrelevant. It means that where the two disagree, the state floor is the one you can insist on.

Converting a garage or a back room

If the unit fits entirely inside your existing house or an existing accessory structure, with its own exterior door, the rules loosen sharply. No setback applies to that converted space, and the city must approve it ministerially — a checklist review with no hearing and no discretion (§ 66323). You may expand up to 150 square feet beyond the existing structure, but only to make the entrance and exit work. Calabasas mirrors this in its own code, including the 150-square-foot allowance (§ 17.12.170).

Demolishing the garage instead? The city cannot make you replace the parking spaces you lose (§ 66314).

One Calabasas-specific warning: if you are converting a structure that was built without a permit, the city requires a safety inspection by the building official and the fire department first — and once that inspection happens you must correct anything it finds, even if you then withdraw the ADU application (§ 17.12.170). Do not start that clock casually.

Parking, and the five ways out of it

Calabasas asks for one space above the main house's requirement, and tandem parking or a mechanical lift counts. But no space is required at all if the unit is within a half-mile of a regularly scheduled transit stop, inside a designated historic district, part of the existing house or an existing accessory structure, in an area where street permits are required but not offered to the unit's occupant, or within one block of an operating car-share facility (§ 17.12.170). State law backs the same list (§ 66322) and caps parking anywhere at one space per unit or per bedroom, whichever is fewer (§ 66314).

Renting it out — and what you cannot do

You may rent the unit; you may not sell it separately from the main house (§ 17.12.170). Short stays are out: Calabasas prohibits any rental under 30 days anywhere in the city where money changes hands, and repeats the ban specifically for ADUs.

Watch the permit clock too. An ADU permit terminates if construction has not begun within one year, or if work stops for 180 consecutive days (§ 17.12.170).

What this page does not cover

Calabasas's table points several standards back to your underlying zoning district and to overlay zones — front setbacks are simply "as required for the applicable zoning district," and units on septic in the Old Topanga and Calabasas Highlands overlays must meet those zones' own standards (§ 17.12.170). Those district-by-district numbers are not in this section. Start from your zone on the Calabasas code overview, then measure your rear yard before you draw anything.

Sources

• Calabasas Municipal Code § 17.12.170 — Accessory dwelling units
• California Government Code § 66314 — Local ADU ordinances
• California Government Code § 66321 — Size and height limits a city may not impose
• California Government Code § 66322 — Parking exemptions
• California Government Code § 66323 — Units a city must approve ministerially