Multifamily ADU Construction in Calabasas

How Many ADUs a Multifamily Lot Can Add in California

Senate Bill 1211, in effect since 2025, widened what multifamily owners can build. A lot with an existing multifamily building can now gain as many as eight new detached ADUs, capped so the ADU count never exceeds the number of existing apartments. A fourplex could add up to four detached units. A building with ten apartments could add eight.

Conversions are counted separately. Spaces nobody lives in, like a storage room, garage, attic or basement, may be turned into ADUs. Every qualifying building can get at least one such conversion, and larger buildings can convert space equal to a quarter of their apartment count. On a lot where a multifamily building is still in the planning stage, the owner can add up to two detached ADUs.

Where Calabasas-Area Multifamily ADUs Make Sense

Single-family zoning covers the bulk of Calabasas, and its multifamily properties tend to sit closer to the commercial corridors and freeway. Many of them are condominium communities, which bring a separate set of questions about common area ownership and association approval. Rental apartment buildings and duplexes under single ownership are the most direct candidates.

Just over the city line, Woodland Hills and West Hills have a much larger supply of apartment buildings and duplexes. Those properties fall under the City of Los Angeles, which permits multifamily ADUs through the Los Angeles Department of Building and Safety under its own ADU ordinance. We start every multifamily project by confirming which agency has the parcel and what that agency's current submittal requirements are.

Converting Garages and Storage Into Apartment ADUs

Carports, tuck-under garages and storage rooms are the usual conversion targets on older apartment lots. The structure exists, so the work focuses on fire separation from the rest of the building, insulation, windows for light and egress, and new plumbing. Parking removed in a garage conversion does not have to be replaced under state law, though you should think about how tenants will use the remaining spaces.

Converted units inside a larger building need careful fire and sound detailing because they share walls and floors with occupied apartments. We plan the work to limit disruption to tenants, schedule noisy tasks during the day, and keep exits and common paths clear throughout construction.

Detached ADUs on Multifamily Properties

Detached units usually go on open yard space, surface parking areas or the edges of the lot. On a lot with a multistory multifamily building, state law raises the minimum allowed height for a detached ADU to 18 feet. The 4-foot side and rear setbacks also apply, which helps on narrow apartment lots.

The number of units is only part of the planning. Each new ADU needs water, sewer and power, and on a multifamily lot the existing service may already be near capacity. Water and sewer come from the Las Virgenes Municipal Water District inside Calabasas, while properties in Woodland Hills and West Hills are served by the Los Angeles Department of Water and Power. A utility review early on tells us whether a larger meter, a new sewer connection or an electrical service upgrade is required.

Can a Multifamily ADU Be Sold Separately?

Not in most places yet. State law lets an ADU be sold as a separate condominium only where the city or county has adopted an ordinance allowing it. Calabasas' current code bans selling an ADU apart from the main property, a provision HCD questioned in its May 2026 findings letter. Plan multifamily ADUs as rental units unless the local rules change.