ADU Costs in Campbell, California

Planning-level pricing guide by ADUWizard.com
Updated for 2026 budgeting

Campbell gets treated like a footnote to San Jose in most ADU content, and that’s a mistake. It’s a small city, about seven square miles, wedged into the west side of Santa Clara County, but the labor pool, the land values, and the permit office are all part of the same Silicon Valley market San Jose sits in. I’ve priced jobs in both cities in the same month and the bids don’t move much crossing the city line.

What actually sets Campbell apart isn’t the cost of a framing crew. It’s the lot. Most of the city is flat, older, post-war tract housing on parcels in the 5,500 to 7,000 square foot range, and that geometry, combined with Campbell’s own setback and separation rules, decides more about your ADU than almost anything else on this page.

Quick disclaimer: This is a budgeting guide, not a quote or legal advice. Bids swing on lot access, existing utility capacity, design scope, and finish level. Use these ranges to sanity-check bids, not as a price.

What Changed in Campbell for 2026

Locally, not much moved on paper, but two things are worth knowing before you budget.

First, Campbell’s ADU Express Plan Check program, which promised a one-week turnaround for two qualifying applicants a week, is currently suspended according to the city’s own Building Division page. The Preapproved Plan Gallery is still live and still worth checking before you draw anything custom, it just isn’t paired with the express review track right now.

Second, the city’s Master Fee Schedule ticks up every July 1 under a Consumer Price Index adjustment written into the ordinance itself. The park in-lieu fee for an ADU at 750 square feet or larger moved from $9,129 in the FY 2025-26 schedule to $9,328 in the FY 2026-27 schedule, effective July 1, 2026, the one now current as of this writing. Small increase, but it tells you these numbers aren’t static, and you should pull the current schedule before you finalize a budget.

On the state side, four bills matter here regardless of what Campbell does locally: AB 1154, AB 462, SB 543, and the 2025 SB 9 amendment giving California’s Housing and Community Development department authority to void local ADU ordinance provisions that conflict with state law, all effective January 1, 2026. Two of them intersect with Campbell’s own published rules in a way worth flagging honestly.

SB 543 changes how ADU size gets measured statewide, shifting to interior livable space. Campbell’s own March 2025 ADU Bulletin already defines “living space” as interior habitable floor area, not garage or accessory space, which happens to be the same standard. That’s not a coincidence I can fully explain, but it means this particular change probably doesn’t shift anything on the ground in Campbell.

AB 1154 is the one I’d actually call and confirm. It narrows the JADU owner-occupancy requirement so it only applies when the JADU shares a bathroom with the main house. Campbell’s published ADU Bulletin, which predates AB 1154’s effective date, still states owner occupancy is required for any JADU, full stop, with a recorded deed restriction. I could not verify whether the Planning Division has updated that guidance since January 1, 2026. If you’re planning a JADU with a fully separate bathroom, ask the Planning Division directly which standard currently applies before you record anything.

What an ADU Actually Costs in Campbell

Budget somewhere between $155,000 and $600,000 depending on type and size, with most detached new-builds landing in the $340,000 to $500,000 band once you add real finishes and a normal contingency. That’s close to what I’d quote in San Jose, and for the same reason: the same electricians, framers, and plumbers bid both cities.

Honestly, the part that surprises people isn’t the construction number. It’s how specific and how real Campbell’s own fee schedule is. Most cities I work in won’t give you an exact dollar figure for anything, they point you to an interactive calculator and shrug. Campbell publishes an actual Master Fee Schedule with line items, percentages, and per-square-foot rates, and that means I can show you real math instead of a vague range. More on that below.

For the state-level picture and how Campbell stacks up against cheaper inland markets, see our California ADU cost guide. Our Data Hub tracks these ranges as bids come in.

Component	Cost range	Notes
Site work and utilities	$15,000-$45,000	short trenching runs on flat lots, longer if the panel needs upgrading
Foundation	$20,000-$45,000	slab-on-grade is standard on Campbell’s flat lots
Framing and shell	$60,000-$140,000	biggest swing driver alongside finish level
MEP (electrical, plumbing, HVAC)	$45,000-$90,000	all-electric equipment required under Campbell’s 2024 air quality ordinance
Interior finishes	$45,000-$110,000	Silicon Valley finish expectations push this up
Design and engineering	$15,000-$35,000	lower with a preapproved plan
Permits and city fees	$7,700-$17,100	swings almost entirely on whether the ADU is 750 sf or larger

Source: ADU Wizard builder estimate

Size	Low finish	Mid finish	High finish
400 sf	$155,000	$185,000	$220,000
600 sf	$210,000	$260,000	$310,000
800 sf	$300,000	$370,000	$440,000
1000 sf	$390,000	$470,000	$550,000
1200 sf	$460,000	$540,000	$620,000

Source: ADU Wizard builder estimate

Fees and Exemptions in Campbell

Here’s the part I actually like about this city: I don’t have to hedge as much as I do elsewhere. Campbell’s FY 2026-27 Master Fee Schedule, effective July 1, 2026, lists real percentages and dollar figures, not a black-box calculator.

Run the numbers for an 800 square foot detached ADU on an example $200,000 permit valuation (that’s the building department’s own valuation for fee purposes, usually well under your actual contract price with a builder):

Fee	Amount	Basis
Building permit fee	$4,000	2.00% of first $500,000 of valuation
Plan check	$1,320	33% of building permit fee
Title 24 plan check	$237	flat
Fire plan check	$400	greater of $119 flat or 10% of building permit fee
General Plan Maintenance Fee	$320	0.16% of valuation
Technology Enhancement Fee (Building)	$80	0.04% of valuation
Training and Education Fee	$40	0.02% of valuation
Construction License Tax	$400	$0.50 per sq ft, CMC Chapter 3.40
Strong Motion Instrumentation Fee	$26	valuation x .00013
Building Standards Fee (SB 1473)	$8	state-mandated valuation tiers
Planning post-entitlement plan check (detached ADU)	$259	flat
Roadway Maintenance Fee	$640	0.32% of building permit valuation
Subtotal, no park fee	≈ $7,730
Park in-lieu fee, ADU 750 sf or larger	$9,328	capped, per state law formula, Master Fee Schedule
Total if 800 sf	≈ $17,058

Source: City of Campbell FY 2026-27 Master Fee Schedule, effective July 1, 2026, and Campbell’s Accessory Dwelling Unit Bulletin

That park fee line is the whole story. Junior ADUs owe $0 in park fees outright. ADUs under 750 square feet also pay $0, because California’s impact-fee exemption for small ADUs applies statewide and Campbell’s schedule explicitly caps the ADU park fee to what state law requires. Cross 750 square feet and Campbell bills you $9,328, current as of the July 2026 schedule. That’s a single design decision worth roughly ten thousand dollars, which is a bigger lever than almost anything else on this page.

I looked specifically for a Campbell-only ADU fee waiver, something like Los Angeles’s park fee exemption that goes beyond the state minimum, and I didn’t find one. Every ADU-specific fee line I could locate in Campbell’s schedule and its ADU Bulletin traces back to the state’s own under-750-square-foot exemption, not a local add-on. If you’ve heard otherwise, I’d confirm directly with the Planning Division at (408) 866-2140, but based on the published fee schedule and ordinance, Campbell isn’t waiving anything beyond what state law already forces.

There’s also a small storm drain area fee, $2,120 per acre of R-1 land, that applies on a whole-site basis and isn’t clearly prorated to just the ADU footprint in the published schedule. Confirm the exact amount with Public Works Engineering before you budget it in, since I can’t responsibly guess how they prorate it for a partial-lot addition.

Campbell-Specific Factors That Move the Number

Tight, older lots. A lot of Campbell’s housing stock is 1950s and 1960s tract construction on parcels smaller than what you’d find in newer subdivisions elsewhere in the county. Combined with the local rule requiring 10 feet of separation from the primary dwelling (or 5 feet if the ADU sits beside the house) plus 4-foot side and rear setbacks, a mature tree or an existing pool can eat your usable footprint fast.

The city’s own air quality ordinance. Campbell adopted a rule effective September 3, 2024 banning NOx-emitting appliances, meaning gas furnaces and gas water heaters, in new residential construction. That’s fine on paper, heat pump water heaters and heat pump HVAC are increasingly standard anyway, but on an older home with a 100-amp electrical panel, it can mean a panel upgrade you weren’t planning on. Budget for that conversation with your electrician early, not after plan check flags it.

Flat terrain is a real cost break here. Unlike San Jose’s hillside neighborhoods around Almaden and Evergreen, Campbell has essentially no hillside grading or geotechnical premium to worry about. Utility trenching runs are short because the city is small and gridded. That’s one place Campbell genuinely beats its bigger neighbor on cost, not a footnote.

Historic properties carry their own rulebook. If your home is listed on the California Register of Historical Resources, and Campbell’s older core has some, a detached ADU has to sit behind the house on the rear half of the lot, tops out at 18 feet instead of the standard 20, and has to visually match the primary dwelling’s cladding, roof form, and window trim. That’s a real design and cost add, not a formality.

Attached and converted ADUs face real design rules that detached ones skip. Campbell’s Bulletin is explicit: detached ADUs aren’t subject to design standards at all. Attached and converted units are, down to specifics like removing a converted garage door entirely and infilling the opening to match the house’s existing materials and color. If you’re pricing a garage conversion as the cheap option, budget that infill work, it isn’t optional.

What I’d Budget If I Were Building Here

If I were building an 800 square foot detached ADU in Campbell today, I’d budget $370,000 to $420,000 all-in, and I’d seriously consider clipping the design to 749 square feet or under. That one decision moves roughly $9,300 in city fees, and on a unit that size the difference between 749 and 800 square feet in usable living space is genuinely small.

That said, if your goal is a real two-bedroom rental unit and 800 square feet is what the layout needs, don’t distort the design to chase a fee line. Pay the $9,328 and build the unit that actually rents well. For the mechanics of getting there, our permits pillar and the California state permit page cover what changes once you’re outside city limits.

FAQs

How much does an ADU cost in Campbell in 2026?

Budget roughly $155,000 for a small conversion up to $600,000 for a large, high-finish detached unit, with most detached new-builds landing between $340,000 and $500,000. Pricing tracks close to neighboring San Jose because both cities draw from the same labor market.

Does Campbell waive any ADU fees beyond what the state requires?

Not that I could find. Every fee exemption in Campbell’s Master Fee Schedule and ADU Bulletin, including the $0 park fee for ADUs under 750 square feet and for JADUs, traces back to California’s own statewide impact-fee exemption, not a Campbell-specific add-on. Confirm with the Planning Division at (408) 866-2140 if you’ve heard otherwise.

Is Campbell’s Express Plan Check program still available?

No, it’s currently suspended according to the city’s Building Division page, though the timeline for reinstatement wasn’t published as of this writing. The Preapproved Plan Gallery is still active and still worth checking before designing custom.

Do I need design review to build an ADU in Campbell?

Not for a detached ADU, Campbell’s own ordinance exempts detached units from design standards entirely. Attached and converted ADUs do face specific design rules, including matching materials on a converted garage, and properties on the California Register of Historical Resources face additional placement and height rules regardless of ADU type.

Do I need to live on the property to build an ADU in Campbell?

No, not for a standard ADU. Owner occupancy is only required for a Junior ADU, and it requires a recorded deed restriction before the city issues your building permit. Standard detached, attached, and converted ADUs carry no occupancy requirement under Campbell’s published rules.