ADU in Martinez, CA
ADU Design & Permitting in Martinez usually starts with the garage, not the backyard. The city’s pre-WWII housing stock means most accessory units begin life as a detached garage with knob-and-tube wiring, a corroded galvanized supply line, and a slab that never met modern code. We scope those hidden costs before drawings start so the written price holds. Call (971) 497-2402 when you want the real number, not a teaser.
Why Martinez Homes Are Different
Martinez is the county seat, with its own building department that has inspected these houses for generations. The Estudillo and Alhambra districts, plus the streets around downtown, are dense with 1900s-to-1940s Victorians and Craftsman bungalows on narrow lots with detached rear garages. Those garages were built for a Model A, not a living space, and the inspectors know exactly where the failures are.
The Carquinez Strait funnels afternoon wind through the gap all year, and that wind hits the windward face of any new structure harder than it does in Concord or Pleasant Hill. Air sealing and moisture management on that face are not optional details; a contractor who learned ADU envelopes in sheltered Walnut Creek will underspec them. Original galvanized plumbing, sub-panel electrical, and shallow slabs show up on nearly every pre-1950 conversion we scope in Martinez. None of this is disqualifying; it just has to be priced before anyone swings a hammer.
Our Main Martinez Services
The two jobs Martinez homeowners call about most are garage conversions and new detached units. Each has its own page with local pricing and conditions.
Garage Conversion ADU in Martinez
Most Martinez garages from the 1920s and 30s were never intended to hold a kitchen or a bathroom. The slab is thin, the electrical is often original knob-and-tube, and the galvanized supply lines have spent 80 years fighting the local water. A Garage Conversion ADU in Martinez means replacing those systems, not hiding them. The city’s inspectors look at foundation condition and panel capacity on these conversions very closely, so we pull the structural inspection early and price the replacement work before the permit set is drawn.
New Detached ADU in Martinez
On the narrow lots common in the Estudillo and Alhambra districts, a new detached unit often tucks into the rear yard where the old garage stood, or beside it if the garage stays. The wind off the Carquinez Strait means the building envelope needs proper air sealing from day one. A New Detached ADU in Martinez starts with a site assessment that accounts for setback requirements, soil conditions, and panel capacity before the floor plan is set.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
- 2
You get an upfront price rangeHonest numbers before anyone is dispatched.
- 3
A background-checked tech heads outLicensed & insured, dispatched right away.
- 4
You approve before work beginsNothing starts until you say go.
ADU Design & Permitting in Martinez
ADU Design & Permitting in Martinez is where most projects either succeed or quietly die. The city operates its own building department, and its inspectors know the pre-1950 housing stock intimately. That means foundation condition, panel capacity, and the structural soundness of an old garage get scrutinized far more closely here than in newer Contra Costa suburbs. Our ADU Design & Permitting service handles the drawings, the permit set, and the city’s questions as one written scope. The Carquinez Strait wind and the older stock both shape the spec, and we price for them up front.
Site Assessment
Signs you need it
You’re looking at a detached garage on a narrow Estudillo or Alhambra lot and need to know whether it can convert, or whether the slab has to come out.
What it costs in Martinez
A site assessment in Martinez typically runs $700-$1,200, depending on access and whether we need to open walls or test the slab.
How we do it
We inspect the foundation, electrical panel, plumbing supply, and lot setbacks, then give you a written condition report with photos and a priced scope.
ADU Design & Blueprints
Signs you need it
You have a garage or interior space and need a permit-ready set that accounts for Martinez’s wind exposure and older framing.
What it costs in Martinez
ADU design and blueprints in Martinez typically run $4,500-$9,500 for the full permit set, depending on unit size and structural complexity.
How we do it
We measure, model, and draft the set, then run Title 24 energy calculations and structural review before the plans go to the city.
Permit Application
Signs you need it
You want someone else to sit through plan check with a building department that knows every pre-1950 garage in Martinez by address.
What it costs in Martinez
Permit expediting and city submittal in Martinez typically run $2,000-$4,500 per application, plus the city’s own fees.
How we do it
We submit the full permit set, respond to plan-check comments in writing, and track the application until the permit is issued.
What ADU Design & Permitting Costs in Martinez
| Item | Typical range in Martinez |
|---|---|
| Site assessment and condition report | $700-$1,200 |
| Full permit set and blueprints | $4,500-$9,500 |
| Permit application and city submittal | $2,000-$4,500 |
How long does ADU permitting take in Martinez?
Plan check at the City of Martinez typically takes 6 to 12 weeks for a complete set. Incomplete drawings or a skipped structural inspection add months. Call (971) 497-2402 and we’ll tell you what your specific project is facing.
Will my old Martinez garage pass a structural review?
Most pre-1950 garages in Martinez need slab replacement or reinforcement before conversion. Our site assessment answers this in writing with photos before you spend on drawings. Call (971) 497-2402 to schedule one.
Junior ADU & Interior Conversion in Martinez
Junior ADU & Interior Conversion in Martinez is often the cleanest path when the lot is too narrow for a detached unit and the garage is too far gone to convert economically. These projects live inside the existing envelope, which means fewer foundation surprises but more attention to the older framing and aging systems common around downtown. Our Junior ADU & Interior Conversion service covers everything from a converted primary bedroom wing to a full basement buildout, with the same written price before work starts. The Strait wind matters less here, but fire separation and egress requirements from the city are just as strict.
Room-to-ADU Conversion
Signs you need it
You have an underused bedroom suite or a large finished room with its own entrance and want it permitted as a legal JADU.
What it costs in Martinez
A room-to-ADU conversion in Martinez typically runs $80,000-$150,000 all-in, depending on whether you add a kitchenette and bathroom.
How we do it
We verify egress, fire separation, and ceiling height, then update the drawings, permit the conversion, and build it out under one contract.
Attached Addition ADU
Signs you need it
You have a ground-floor wing or a rear addition that can become a self-contained unit without changing the home’s footprint.
What it costs in Martinez
An attached addition ADU in Martinez typically runs $150,000-$250,000 all-in, with the higher end reflecting structural tie-ins to older framing.
How we do it
We design the separation, run electrical and plumbing from the main panel, and build the interior to code, including sound attenuation and fire walls.
What Junior ADU & Interior Conversion Costs in Martinez
| Item | Typical range in Martinez |
|---|---|
| Room-to-ADU conversion (JADU) | $80,000-$150,000 |
| Attached addition ADU | $150,000-$250,000 |
| Basement ADU buildout | $120,000-$220,000 |
Can I put a JADU in my Martinez Victorian?
Yes, most Victorians in the Estudillo and Alhambra districts have large rooms with high ceilings that convert well. Fire separation and a separate entrance are the two items the city checks first. Call (971) 497-2402 for a written scope.
Do interior conversions need their own utility connections?
Usually not, which is why they cost less than detached units. The existing panel and plumbing can often serve the new unit, but we verify capacity before pricing. Call (971) 497-2402 to confirm.
ADU Site Prep & Utilities in Martinez
ADU Site Prep & Utilities in Martinez is where the hidden money lives. The original galvanized plumbing, undersized electrical panels, and shallow slabs that turn up in pre-1950 homes around downtown have to be replaced before any living space can be permitted. Our ADU Site Prep & Utilities service handles the foundation, the panel, the laterals, and the gas line as one scoped line item with a written price. The city’s inspectors look for exactly these conditions on older lots, and we would rather find the corroded pipe in the bid than have the inspector find it mid-construction.
Foundation & Grading
Signs you need it
Your garage slab is cracked, thin, or built without rebar, and the city will not sign off on a conversion until it’s replaced or reinforced.
What it costs in Martinez
Foundation replacement or reinforcement for a garage conversion in Martinez typically runs $15,000-$35,000, depending on slab size and soil conditions.
How we do it
We saw-cut and remove the old slab, grade the subgrade, pour a new reinforced slab per engineering, and document every step with photos.
Electrical Panel Upgrade
Signs you need it
Your main panel is a 60-amp or 100-amp unit from the original build, and the ADU needs its own subpanel or a service upgrade.
What it costs in Martinez
A main panel upgrade in Martinez typically runs $3,000-$6,500, and a new subpanel run to the ADU adds $1,500-$3,000.
How we do it
We pull the load calculation, size the new panel, coordinate with the utility, and run the subpanel feeder to the ADU location.
What ADU Site Prep & Utilities Costs in Martinez
| Item | Typical range in Martinez |
|---|---|
| Foundation replacement or reinforcement | $15,000-$35,000 |
| Electrical panel upgrade | $3,000-$6,500 |
| Plumbing lateral and gas line extension | $6,000-$14,000 |
Do all Martinez ADUs need a panel upgrade?
Most pre-1950 homes in Martinez do, because the original panel cannot carry a second living unit. We verify actual load before pricing the upgrade. Call (971) 497-2402 for a written assessment.
Can I keep the old garage slab?
Rarely in Martinez. The city requires slab thickness and reinforcement that 1920s-era pours do not meet, and inspectors check this specifically. Our foundation crew confirms condition in the site assessment. Call (971) 497-2402 to schedule one.
Brands We Service in Martinez
We specify and coordinate prefab and modular systems from Cover, Dvele, and Mighty Buildings within the same single contract. Parts and panels are staged regionally, which keeps turnaround predictable for Martinez sites. See our brands for the full list.
Pricing for ADU in Martinez, CA
| Service | Typical range in Martinez |
|---|---|
| Site assessment and condition report | $700-$1,200 |
| Full permit set and blueprints | $4,500-$9,500 |
| Permit application and city submittal | $2,000-$4,500 |
| Room-to-ADU conversion (JADU) | $80,000-$150,000 |
| Attached addition ADU | $150,000-$250,000 |
| Basement ADU buildout | $120,000-$220,000 |
| Foundation replacement or reinforcement | $15,000-$35,000 |
| Electrical panel upgrade | $3,000-$6,500 |
| Plumbing lateral and gas line extension | $6,000-$14,000 |
What pushes a Martinez project toward the top of these ranges is the age of the structure. Knob-and-tube rewiring, full slab replacement, and main panel upgrades are more common here than in Concord or Pleasant Hill because the housing stock is forty years older. Every price on this page is a written price before work starts, per Haven Standard Clause 1. You will never hear “call for a quote” from us.
Neighborhoods We Serve in Martinez
We cover the full city of Martinez, with most of our ADU work concentrated in the older neighborhoods where conversions are most common. Our crews are in the area weekly, and scheduling is typically within a few business days for a site assessment.
- Estudillo District
- Alhambra District
- Downtown Martinez
- Mountain View
- Virginia Hills
Service Area - Cities Near Martinez
In addition to Martinez, our crews serve the surrounding Contra Costa and Solano communities: Pleasant Hill, CA, Benicia, CA, Lafayette, CA, and Concord, CA. Each city has its own permitting quirks, and we scope for them the same way we do here.
Serving Martinez, CA - Our Local Coverage Area
We’re based in the Martinez area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs About ADU in Martinez
Yes. Martinez is the county seat and operates its own building department, so ADU permits are handled by local inspectors who know the older housing stock. That local knowledge means foundation and panel conditions on pre-1950 conversions get a close look. Call (971) 497-2402 to get your project scoped by someone who knows what those inspectors check.
Most Martinez ADU work is in older neighborhoods without HOAs, but a few planned communities exist on the outskirts. State law limits what HOAs can prohibit, but we verify any covenants during the site assessment. Call (971) 497-2402 to check your lot.
Site assessments are typically scheduled within a few business days, and design work starts once the assessment is complete. The longest variable is city plan check, which runs 6 to 12 weeks in Martinez. Call (971) 497-2402 and we’ll map the whole timeline for your project.
What happens when you call
- 1A real person answersNo phone trees - talk to a local adu pro.
- 2You get an upfront price rangeHonest numbers before anyone is dispatched. No surprises.
- 3We come out and measureLicensed & insured, at a time that suits you - the visit and the quote are both free.
- 4You get the price in writingLine-itemed, yours to keep, and nothing starts until you say go.
What Martinez Customers Say
"The rental income has covered the payment since the second month. They were realistic about the numbers rather than optimistic."
- Odette N."They walked us through setbacks and utility capacity before we paid anything, and told us one of our two options was not going to get approved."
- Mireille T."Every allowance was itemised at the start, so the finish selections did not turn into a surprise at the end."
- Benedict H.