← PCG Engineering
Permit guides
ADU Permits in Campbell: 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 or county before you build.
Who handles your permit
The City of Campbell Building Inspection Division, 70 North First Street, Campbell, CA 95008 — (408) 866-2130, building@campbellca.gov. All building permit applications go through the city's online system, MyGovernmentOnline (MGO); everything is submitted digitally. For zoning or land-use questions, the Planning Division (same address) is at (408) 866-2140 or planning@campbellca.gov.
What you can build
California state law sets the baseline, and Campbell adds a few local signatures:
1,200 sq ftState max for a detached ADU (800 sq ft guaranteed)
500 sq ftMax for a Junior ADU, within existing footprint
-B / -CSeparate addressing: your house number plus -B for an ADU, -C for a JADU
MGOThe online portal where every Campbell building permit is filed
On-site waterStormwater must be retained on your lot — drywells or pop-up emitters, not the street
WVSDWest Valley Sanitation District signs off on sewer connections and backflow
Campbell expects an ADU to provide a means to cook and to meet the same design and habitability standards as a single-family home. JADUs get softer requirements — an efficiency kitchen and shared elements with the main house are allowed.
Campbell shows its hand before you draw
Campbell publishes sample plan-check checklists for a new ADU and for a garage conversion to ADU — annotated examples of exactly what reviewers look for on the site plan, structural sheets, and supporting documents. Reading those before drawing is the closest thing to seeing the test before you take it. On top of that, Campbell joined the county-wide aduscc.org collaborative with other Santa Clara County cities, which offers a free step-by-step ADU guidebook, sample floorplans, and a cost-and-rent calculator. The city doesn't maintain its own preapproved plan library, so these resources are the head start instead.
What goes into the submittal
- Plan set through MGO — site plan, floor plans, elevations, structural plans and details, electrical/plumbing/mechanical layouts.
- A thorough site/plot plan — setbacks with distances, trees, hard surfaces, exterior appliances, and every detached structure.
- Stormwater retention plan — roof gutters and downspouts connected to subsurface drains ending in drywells, pop-up emitters, or retention basins in the front or back yard.
- Electrical routing — location and size of the main panel, whether service wires are overhead or underground, and how power reaches the ADU's sub-panel (wire size, conduit, burial depth).
- Sewer and water details — sewer pipe size and location with cleanouts or backflow devices per West Valley Sanitation District; water meter location and the ADU connection with pipe size and shutoff valve.
- Structural calculations and Title 24 energy forms as required for the scope.
Where applications usually get stuck
- The stormwater retention plan. Roof runoff kept fully on site is non-negotiable in Campbell, and small backyards make drywell placement tricky.
- West Valley Sanitation sign-off. Sewer lateral standards, backflow prevention, and district fees run on their own track alongside the city review.
- Electrical service capacity. Undersized panels or vague routing from the main house to the ADU draw corrections every time.
- Garage conversions. Changing a garage to living space means foundation, ceiling height, insulation, egress, and fire separation — it's never just drywall.
- JADU deed restriction. Junior ADUs require a recorded Notice of Restriction — paperwork that gets forgotten until issuance.
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.