The Complete Los Altos ADU Requirements Guide
Building an accessory dwelling unit (ADU) in Los Altos starts with knowing what’s actually required. An ADU is a separate, self-contained living space on the same property as your main home—detached, attached, or carved out of existing square footage. It can create rental income, house family members, or just give you more options on a property you already own.
Los Altos operates under California’s statewide ADU framework, which sets baseline standards every jurisdiction must follow. Cities can layer on objective requirements, but they can’t block ADUs that meet state minimums. What follows is a breakdown of the rules that matter: dimensions, setbacks, parking, design standards, and how Samara can help you get it done from start to finish.
Los Altos ADU regulations at a glance
Los Altos reviews ADU applications ministerially—no discretionary hearings, no public comment periods. If your project meets state-mandated standards, the city has to approve it regardless of what local zoning would normally allow.
Permit timelines in Los Altos typically run three to four months. The city maintains a Pre-Approved ADU Program with free permit-ready plans, which can cut down on design and review time.
Size and lot requirements
Los Altos requires a minimum of 150 square feet for any ADU. Maximum size varies by type:
- Detached ADUs max out at 1,200 square feet under local code, but state law guarantees at least 800 square feet no matter what. The standard height limit is 16 feet. On multifamily properties or within half a mile of transit, that increases to 18 feet, with an additional two feet (to 20 feet total) allowed if the roof pitch matches the primary dwelling.
- Attached ADUs are also capped at 1,200 square feet. State law requires cities to allow at least 850 square feet for a studio or one-bedroom, or 1,000 square feet for units with two or more bedrooms. These can reach 25 feet in height or the primary dwelling’s height limit, whichever is lower.
- Junior ADUs (JADUs) are limited to 500 square feet and must be contained entirely within the walls of the main home. JADUs require an efficiency kitchen and can share a bathroom with the main house.
New detached ADUs must have at least 4-foot side and rear setbacks. Conversions of existing spaces don’t trigger setback requirements. In flood zones and areas with specific safety overlays, height limits may be increased to meet safety standards.
Meet the KurodasDesign requirements
Los Altos enforces objective design standards, which means measurable criteria rather than subjective judgment:
- Detached ADUs that are visible from the street should use roof forms, exterior materials, and colors that are compatible with the primary home.
- Attached ADUs must generally match the appearance of the primary residence and avoid altering the street-facing facade beyond objective allowances.
- Historic districts can apply additional objective design criteria, but they are not allowed to block an ADU outright.
The standards exist to preserve visual consistency without giving planners discretion to deny projects on aesthetic grounds.
Parking requirements
Off-street parking isn’t required for ADUs or JADUs in Los Altos. You also don’t have to replace parking if a garage, carport, or covered parking structure is removed or converted. As of January 2025, replacement parking is also not required when uncovered parking spaces are demolished for ADU construction. If you add parking voluntarily, tandem and setback configurations are both allowed.
Zoning eligibility
ADUs are allowed on any residential or mixed-use lot, as long as there’s an existing or proposed home on the property. This includes areas with wildfire, flood, or other safety overlays, though additional requirements may apply.
Number of ADUs allowed
On a single-family lot, you can build one full-size ADU (attached or detached), plus one JADU inside the main home.
On a multifamily lot with an existing building, you can build up to 8 detached ADUs, so long as the number does not exceed the count of primary units, plus multiple conversion ADUs within the existing building, up to 25% of the existing unit count.
On a multifamily lot with a proposed building, you can build up to 2 detached ADUs, subject to standard setbacks and height rules.
Owner-occupancy requirements
As of January 1, 2024, California permanently eliminated owner-occupancy requirements for ADUs. You’re not required to live on the property to build or rent out an ADU in Los Altos. However, JADUs remain subject to owner-occupancy requirements, meaning the property owner must reside in either the primary dwelling or the JADU.
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Streamline your ADU project in Los Altos
Homeowners in California typically spend over $250,000 on an ADU, but they’re still more affordable than buying additional property. Even with premium finishes and custom features, total costs usually stay well below half the median California home price, which reached $784,989 in 2024. Samara’s ADUs start at $147,000 plus installation.
If you’re looking to build an ADU, Samara makes it easy. We handle everything from permits to installation and even offer our own financing. Call us at 650-420-2607 to schedule a 15-minute consultation and discover how simple adding a Backyard ADU can be.
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