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Completed detached ADU with finished stucco exterior in Santa Clara County

High Demand

Accessory Dwelling Units

A second home on your lot — for family, for rental income, or for the value it adds. Built by a licensed general contractor, not assembled by a broker.

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  • Licensed CA General B #1112902
  • Fully Insured
  • Santa Clara & San Mateo Counties
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The short answer

A good-quality ADU in Santa Clara or San Mateo county runs $300K–$360K for a good-quality build. We publish that as a project range and never as a price per square foot, because roughly $13,500–$18,500 of soft costs — plans around $10,000, survey and certification about $3,000, and soils work from $4,500 — are fixed no matter how small the unit is. That is why a 400 sq ft unit is not two-thirds the price of a 600 sq ft one, and why any contractor quoting ADUs off a flat per-foot multiplier has not priced one properly. Since 1 January 2025, AB 1332 also requires every California city to run a pre-approved ADU plan programme with a 30-day ministerial approval clock — worth asking about before anyone draws anything.

Licence
CA General B #1112902
Bond & insurance
$25,000 bond, insured
Permits
We pull and close them
Where
Santa Clara & San Mateo

The rules change at every city line

An ADU is a small building with a full building's worth of requirements: its own permits, its own utility connections, setbacks, fire separation and inspections. California law has opened ADUs up considerably, but what's actually allowed on your lot depends on your city, your parcel and your existing structures.

That's the part worth getting right before you spend money on drawings. We look at the lot first — where it can go, how utilities reach it, what the city will want — and tell you what's realistic. An ADU that can't get a permit is an expensive set of plans.

Scope

What an ADU project involves

Lot feasibility

Where a unit can physically and legally sit — setbacks, existing structures, access and utility routing.

Permits

City submittal and plan check. Requirements differ from one city to the next, which is why each of our city pages exists.

Utilities

Water, sewer and electrical service to a second dwelling — often the line item people don't see coming.

Foundation & framing

A full structure: foundation, framing, weather barrier, windows and roof.

Full interior

Kitchen, bath, mechanical, electrical and finishes — a complete, permitted dwelling.

Final inspection & sign-off

Through to certificate of occupancy, so it's legally rentable and adds documented value.

Which kind of ADU fits the lot

Which kind of ADU fits the lot
DetachedGarage conversionJunior ADU (JADU)
Where it goesNew structure in the rear yardInside the existing garage footprintInside the existing house
Adds footprintYesNo — converts itNo
Foundation workFull new foundationUsually slab remediation onlyNone
UtilitiesNew runs; may need a service upgradeShorter runs, often simplerUsually shares the house
Parking replacementNot triggeredOften the sticking pointNot triggered
Usual reason to choose itMost rentable, most privateCheapest route to a real unitSmallest scope, fastest

Common Questions

Straight answers

Can I build an ADU on my lot?
Usually, but it depends on your city, your parcel and what's already on it. State law has made ADUs far easier across California; the specifics — setbacks, height, utility routing — are local. That's the first thing we check, before you spend anything on drawings.
How much does an ADU cost in San Jose?
It depends far more on utilities and site conditions than on square footage — running sewer and electrical service to a second dwelling is often the line people don't budget for. Our projects generally start at $20,000 and run to $350,000+ depending on scope. We'll give you a real range on a discovery call rather than a number designed to win the job.
Can I rent it out?
Once it's permitted and has passed final inspection, yes — that's the point of building it legally rather than converting a garage without permits. An unpermitted unit is a liability at sale and often uninsurable.
Can I build an ADU on my lot?
Usually, but the honest answer is per-parcel. What decides it is rear-yard space after setbacks, access for utilities, and whether your electrical service can carry another dwelling. California law has made ADUs broadly permissible statewide, so the question is rarely allowed and almost always where it physically fits and what the utilities cost. That is worth answering before you pay anyone to draw something.
What is AB 1332 and does it save me money?
Since 1 January 2025, every California city and county — charter cities included — must run a pre-approved ADU plan programme and must approve or deny a ministerial application using a pre-approved plan within 30 days. It matters for two reasons: the roughly $10,000 plan cost stops being a per-job expense once a model is approved, and permit time collapses from months of plan check to a 30-day clock. Ask every city whether they have one. Pre-approval is tied to the current triennial building code cycle, so plans need re-approval each cycle.
Why are two ADU quotes for the same size $80,000 apart?
Usually because one of them has not included the soft costs. Plans, survey and certification, and soils work together run roughly $13,500 to $18,500 and are fixed regardless of unit size. Add utility runs, a possible service upgrade, site access and demolition, and two bids for ‘a 600 square foot ADU’ can describe genuinely different scopes. Compare what is excluded, not what is included — the exclusions are where the difference lives.
Does an ADU need its own utility connections?
Usually its own electrical subpanel, and often its own water and sewer laterals depending on the city and the distance from the main. The item that surprises people is service capacity: adding a dwelling can push an older 100-amp service past what it can carry, which means a service upgrade before anything else happens. That gets checked at the site visit, not discovered at inspection.
Can I rent out an ADU?
Generally yes for long-term tenancy — that is much of the point of the state ADU laws. Short-term rental rules are set locally and vary city by city, so check your own city's ordinance before you build around that assumption. We build the unit; we do not give legal or tax advice on how you let it.
Are you licensed, bonded and insured?
Yes — California General Building (B) license #1112902, a $25,000 contractor bond, and an active workers' compensation policy with The Hartford. Verify the license on the CSLB registry. Certificates of insurance are available on request.
Do you handle the design?
We build your vision — we're not designing the place with you. But "we don't design" does not mean "you're on your own for plans." We coordinate the architect and structural engineer who produce your stamped permit set, including Title 24, and they submit to the city portal. That is a line item we price and manage — on an ADU it runs about $10,000 and it is in the estimate, not a homework assignment we hand you.

On ADUs we can also start from a standard design and give you a materials list, which is usually the faster and cheaper route.

What we won't do is sit and choose your layout, cabinet doors and finishes with you. That is interior design, it is a real skill, and it isn't ours — if that's the help you want we'll say so up front rather than three weeks in.
How do allowances work?
An allowance covers work nobody can honestly price until something is opened up. Those are billed at actual cost, and whatever isn't spent comes off your final invoice. We'd rather show you the unknowns than bury them in a padded fixed price.

Process

How an ADU project actually runs

  1. Site visit and feasibility

    We look at the rear yard against setbacks, walk the access route, find where the utilities come in, and open your electrical panel. That is usually enough to tell you which ADU type your lot supports and what the site conditions will add.

  2. Plans and soft costs

    Plans, survey and certification, and soils work. Roughly $13,500 to $18,500, and largely fixed regardless of unit size — which is exactly why we do not price ADUs per square foot. Where your city runs a pre-approved plan programme under AB 1332, this is where that can change the maths.

  3. Permit

    Submission and plan check. A pre-approved plan carries a 30-day ministerial clock; a custom set goes through normal review.

  4. Utilities and service capacity

    Water, sewer and electrical get run. If your existing service cannot carry another dwelling, the upgrade happens here — and it was identified at the site visit rather than discovered now.

  5. Foundation and shell

    Foundation, framing, roof and dry-in. On a garage conversion this step is mostly slab remediation instead.

  6. Trades, finishes, final

    Rough-in, inspections, insulation, drywall, finishes, then final inspection and close-out. You end up with a permitted, legal dwelling — which is the whole point, and the thing an unpermitted conversion never gives you.

Deposit is capped at $1,000 by California law. Milestone draws follow the work — see how payments work.

Before you sign anything

Worth reading first

All guides →

Service Area

Where we build

Permit process, plan check and utility requirements change at every city line. Each page covers what's actually true where you're building.

Tell us about your project

Book a 30-minute discovery call and we'll tell you what's realistic — scope, budget and timeline — whether or not we're the right builder for it.

Book a Project Discovery Call Call (408) 597-2733