Los Altos ADU Project 1,200 Sq Ft Detached ADU
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About This ADU Build
This is a 1,200 square foot detached ADU that Axiom Renovation is building in Los Altos, the largest size the City allows for an ADU with two or more bedrooms. The project includes a new 200-amp underground electrical service. We are documenting each stage and will keep this page updated through completion.
Type: Detached ADU (new construction)
Size: 1,200 sq ft
Permitting: City of Los Altos, ministerial ADU building permit
Electrical: 200-amp underground service upgrade, ADU fed from the main house panel, coordinated with PG&E
Status: Insulation stage, October 2026
Build Progress, Summer to Fall 2026
Photos taken by our crew on site. The address and owners are kept private.
Framing: Walls, Vaulted Roof and Sheathing
Framing started in early summer 2026, laid out to the approved City plans. The roof was framed with exposed rafters for a vaulted ceiling, which makes the unit feel larger and brighter, then sheathed and dried in. Detached ADUs in Los Altos can be up to 18 feet tall, which leaves room for a vaulted ceiling on a single story.
Underground Electrical Service
Los Altos requires any new or relocated electrical service to be underground, with no waiver. We trenched a new underground service, upgraded the main service to 200 amps, and fed the ADU from the main house panel through its own subpanel rather than adding a second meter. That meant a load calculation for both units, a single-line electrical drawing for the permit, and an application and coordination with PG&E. Read more in electrical service for a detached ADU in Los Altos.
Rough-In, Shower Pan and Insulation
Plumbing, electrical and mechanical rough-ins were completed together, because Los Altos requires all rough inspections to be ready at the same time. The shower pan was built and tested before tile, and insulation went in after the rough inspections passed, ahead of the insulation inspection and drywall.
Planning a Large ADU in Los Altos
- 1,200 sq ft is the maximum for a detached ADU with two or more bedrooms; ADUs do not count toward the main house floor area.
- ADUs over 750 sq ft need a civil and grading plan with erosion control and stormwater measures.
- State law bars impact fees only on ADUs of 750 sq ft or less, so larger ADUs should plan for them.
- Fire sprinklers are not required if the main house does not require them, subject to fire access and water supply.
See the full Los Altos ADU guide and our backyard ADU in finishes.
More Los Altos ADU Resources
Los Altos 1,200 Sq Ft ADU Project FAQ
How big is this ADU?
1,200 sq ft, the maximum for a detached ADU with two or more bedrooms in Los Altos.
Does the ADU have its own electric meter?
No. It is fed from the main house panel through its own subpanel, after a 200-amp underground service upgrade.
Why underground service?
Los Altos requires new or relocated electrical services to be underground.
When will it be finished?
We will update this page as the build moves toward completion.