Ministerial Approval And Pre-Approved Plans.
Los Altos reviews ADU applications ministerially: no discretionary hearings, no public comment periods. If your project meets the state-mandated standards, the city has to approve it, even where local zoning would normally say otherwise. Permit timelines typically run three to four months.
The city also runs a Pre-Approved ADU Program with free permit-ready plans that can shave time off design and review. Current requirements are posted on the City of Los Altos ADU page, and our free lot check will tell you what fits on your property.
Size And Height Limits.
Any Los Altos ADU must be at least 150 square feet. Detached ADUs max out at 1,200 square feet under local code, and state law guarantees you at least 800 square feet regardless. The standard detached height limit is 16 feet, rising to 18 feet on multifamily properties or within a half mile of transit, and to 20 feet if the roof pitch matches your main home.
Attached ADUs are also capped at 1,200 square feet, with state law guaranteeing at least 850 square feet for a studio or one-bedroom and 1,000 square feet for two or more bedrooms; they can reach 25 feet or the primary dwelling's height limit, whichever is lower. JADUs are limited to 500 square feet and must sit entirely within the walls of the main home. The state's rules are collected in the California HCD ADU Handbook.
Setbacks, Overlays, And Parking.
New detached ADUs need at least 4-foot side and rear setbacks, while conversions of existing space trigger no setback requirements at all. In flood zones and areas with safety overlays, height limits may actually be increased to meet safety standards. Design review is limited to objective, measurable criteria: street-visible ADUs should use roof forms, materials, and colors compatible with the primary home, but planners cannot deny a project on subjective aesthetic grounds.
Parking is a non-issue. Off-street parking is not required for ADUs or JADUs, you do not have to replace a garage or carport you remove, and as of January 2025 that extends to uncovered spaces demolished for ADU construction too.
Who Can Build, And How Many Units.
ADUs are allowed on any residential or mixed-use lot with an existing or proposed home, including properties in wildfire or flood overlay areas, though extra requirements may apply there. Since January 1, 2024, California has permanently eliminated owner-occupancy requirements for ADUs, so you can build and rent one out without living on the property. JADUs are the exception: the owner must live in either the main home or the JADU.
A single-family lot supports one ADU, attached or detached, plus one JADU inside the main home. On a multifamily lot with an existing building you can add up to 8 detached ADUs, as long as they do not outnumber the primary units, plus conversion ADUs up to 25 percent of the existing unit count. A proposed multifamily building allows up to 2 detached ADUs. Building at that scale? See Abodu's multifamily program.
What It Actually Costs.
Custom site-built ADUs in California routinely exceed $250,000 before change orders begin. Abodu takes the guesswork out with transparent published pricing: homes from $234,800 plus a published installation price, an expected all-in from $298,800, covering design, permits, the factory build, delivery, and installation. Take two minutes to see how the process works.