Permit guides

ADU Permits in Sunnyvale: a Homeowner's Guide

What you can build, which permits you need, and how the review actually works — in plain language.

Last updated October 2026. Rules change; always confirm current requirements with the city before you build.

Who handles your permit

Permits run through the City of Sunnyvale's One-Stop Permit Center at City Hall (505 W. Olive Ave.) — one counter staffed by Building, Fire, Planning, and Public Works Engineering. Everything is filed online through E-OneStop Online Services: applications, uploads, correction responses, payments, and inspections. First-timers are encouraged to call planning staff at (408) 730-7440 before filing.

What you can build

California state law sets the baseline, and Sunnyvale follows it:

1,200 sq ftMax for a detached ADU

50% / 1,200Max for an attached ADU (50% of the main home, up to 1,200 sq ft)

500 sq ftMax for a Junior ADU, carved from existing space

16 ftHeight limit for most detached ADUs (18 ft near major transit)

4 ftMinimum rear and side setbacks for detached ADUs

1 + 1One ADU plus one JADU allowed per single-family lot

There is no minimum lot size for an ADU under state law. Converted garages and other existing structures keep their current footprint — no new setbacks apply to the conversion itself.

Two review tracks — the line is 800 sq ft

Streamlined ADUs need only a building permit: new units up to 800 sq ft on single-family lots, new units on multifamily lots, conversion ADUs, JADUs, and ADUs built entirely within a new basement.

Non-streamlined — a new unit over 800 sq ft on a single-family lot — needs a Miscellaneous Plan Permit (MPP) from the Planning Division first.

Pre-approved plans. The city's Plans Gallery lists pre-approved ADU designs you can purchase from the designer — they move through a streamlined permitting process.

Pre-approved doesn't mean permit-free. You still need a building permit, and reviewers still verify site placement, foundation, utility connections, and fire access for your property.

What goes into the submittal

Create your E-OneStop account and pick the right application type (Minor Building Permit, Building Project, or a morning over-the-counter appointment).
Prepare the plan set: site plan, floor plans, elevations, foundation and framing details, structural calculations, Title 24 energy, and MEP layouts — plus the MPP application first if you're over 800 sq ft on a single-family lot.
Waste Management Plan. Since August 2026, Sunnyvale creates a Green Halo project for every permit — completing it is part of the process.
Corrections, fees, permit. The city must act within 60 days of a complete application; each correction round adds weeks.

Where applications usually get stuck

Crossing the 800 sq ft line without realizing a Miscellaneous Plan Permit is required first.
Garage conversions — foundation, ceiling height, egress, and fire separation; never just "add drywall."
Legalizing an unpermitted unit. Units built before January 1, 2020 can qualify for reduced standards, with a five-year deferred enforcement option; newer units follow full new-ADU rules.
Site plan gaps — wrong setbacks, unmarked easements, unclear utility connections.

Not sure where to start? That's the part we do. We look at your property, map the requirements, coordinate the plans and specialists, and manage the submittal and corrections — one point of contact.

Tell us what you need help with.

Not sure where to start? That's what we're here for.

Send your project

Erik — (916) 540-8960 · Vall — (916) 956-8106
office@pcg-engineering.pro