Los Altos ADU Permit & Building Guide
Building an Accessory Dwelling Unit (ADU) in Los Altos is one of the most rewarding investments a homeowner can make. At Apex Homes, we designed and built the City of Los Altos’ Pre-Approved ADU models, giving homeowners a faster path to creating extra living space, generating stable rental income, and boosting property value, all within a streamlined process that can take as little as five months. Whether you are envisioning a detached backyard cottage or a flexible in-law unit, Los Altos offers excellent opportunities for ADU development.
ADU Regulations in Los Altos
Los Altos allows ADUs on both single-family and multi-family lots, with rules varying depending on the property type.
For single-family lots, homeowners can build one detached or attached ADU plus one Junior ADU (JADU). Detached ADUs can be up to 1,200 square feet, while attached ADUs may also reach 1,200 square feet but cannot exceed 50% of the main house’s floor area. JADUs are limited to 500 square feet. Setbacks are generally a minimum of four feet from the side and rear property lines. Height limits allow detached ADUs up to 18 feet and attached ADUs up to 16 feet. Detached units must maintain at least five feet of separation from the main house.
For multi-family lots, homeowners may build up to two detached ADUs, with additional attached ADUs allowed as interior conversions up to 25% of existing units. Detached and attached units follow the same size and setback limits as single-family lots, with detached ADUs up to 18 feet tall, attached ADUs up to 16 feet, and a minimum of five feet separation from the main dwelling.
These standards give homeowners flexibility to add functional, high-quality living spaces while maintaining neighborhood character.
The Los Altos ADU Permitting Process
The permitting process in Los Altos follows California’s streamlined, ministerial approval pathway for ADUs. Homeowners begin by selecting the desired ADU design, ranging from studio to two-bedroom floor plans, and confirming that their property meets zoning, setbacks and lot coverage requirements.
Once eligibility is confirmed, the next step is to prepare and submit required documents, which typically include: site plan, utility layout, boundary survey, architectural plans (or Pre-Approved ADU design selection). Applications are submitted directly to the City of Los Altos Building Department. By state law, the city must review ADU applications within 60 days. Once approved, you can move forward with construction, inspections, and final sign-offs.
Why Build An ADU in Los Altos?
Los Altos is one of Silicon Valley’s most desirable residential communities, and building an ADU here offers multiple benefits. ADUs can boost property values by 25-35% while also generating reliable rental income in a high-demand housing market. Beyond financial advantages, they provide living arrangements, making them ideal for guests who need privacy and comfort. At the community level, ADUs contribute to the local housing supply, foster neighborhood diversity, and make efficient use of existing lots without requiring new infrastructure.