Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
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AfterFast, Reliable Home Additions & ADU Across Martinez
Most home additions and ADU projects in Martinez run $45,000 to $130,000, with detached ADUs landing between $90,000 and $220,000 depending on site conditions and finishes. The number that actually matters here isn’t the square footage, it’s what the strait wind and adobe clay will do to whatever you build. We’ve been framing additions in this city long enough to know that the cheap spec costs more within a decade, and we price the work around that truth from day one. Call (877) 610-1318 and we’ll walk your lot with you before anyone writes a number down.
Martinez isn’t Concord. The wind off the Carquinez Strait doesn’t quit, and the clay under the older blocks doesn’t sit still. If your addition gets specced like an inland job, it fails early – rusted hardware, cracked walls, heaving patios. We spec it for Martinez from the first bolt.
Why Barrett & Sons Construction Is Martinez’s Preferred Home Additions & ADU Company
Tom Barrett started this company in 1998, and his sons run the crews that show up on Martinez jobs today. That’s not marketing language – it’s who answers when you call. Customers here tend to ask the same three questions: who’s on my job, what happens if something’s wrong, and will the price change. The answers are: Tom’s sons and their teams, the 90-Day Done Right Promise in writing, and a written change order before any scope change touches the work.
We know the hillside blocks near the downtown historic district, and we know what’s under them. The permit inspector works for you, not for us – so do we. Every eligible job gets permits pulled and inspections signed, because the last contractor most Martinez homeowners used told them permits were optional. That’s not how we work, and it’s not how this city’s older housing stock survives another hundred years.
When you call (877) 610-1318, a live person answers. Not a voicemail box, not an out-of-state call center. You’ll talk to someone who knows where the job is and what it takes.
Our Home Additions & ADU Services in Martinez
If you’re weighing an addition against an Home Additions & ADU project, the short version is this: room additions make sense when you’re staying put, and an ADU makes sense when you want rental income, a place for family, or both. In Martinez, both routes run into the same two site realities – wind uplift off the strait and expansive clay under the foundation. We design and build around both.
ADU Design & Permitting
Contra Costa County’s ADU rules have shifted over the years, and Martinez’s historic district adds its own layer of review for anything visible from the street. We handle the drawings, the permit package, and the inspections – and we tell you upfront what the city will require before you spend money on a plan that won’t pass. Every allowance and every scope line goes on paper before work begins.
Garage Conversion ADU
A garage conversion in Martinez typically runs $30,000 to $80,000, and it’s often the fastest path to a rentable unit because the shell already exists. What people don’t expect is how much the existing slab matters. Many garages in the older Martinez neighborhoods were poured thin, with no rebar and no vapor barrier – which means the salt air has been working on any embedded anchors for decades. We test and reinforce before we frame.
New Detached ADU
Detached ADUs in Martinez run $90,000 to $220,000, and the spread comes down to site prep, foundation type, and the utility run from the street. On hillside lots with expansive clay, we often specify a raised foundation with proper drainage rather than a slab-on-grade – because a slab that heaves in year two is a repair bill that erases your rental income. Every exterior fastener on our ADU jobs is hot-dip galvanized or stainless, since the marine air off the Carquinez Strait eats bare steel within a decade.
Junior ADU & Interior Conversion
A junior ADU inside your existing footprint is usually the most affordable path to a legal second unit, and it avoids most of the wind and clay issues entirely because you’re not adding a new envelope. That said, the older Martinez homes with original lath-and-plaster walls often hide knob-and-tube wiring and undersized framing – which means the conversion scope can grow once the walls come open. We write that scope in writing before we touch a wall.
ADU Site Prep & Utilities
On the hillside blocks near the historic downtown district, site prep is often the real project. The clay moves seasonally, and trenching for water, sewer, and power across moving ground demands compaction and bedding that an inland crew might skip. We don’t skip it, because an allowance that isn’t on paper is a surprise waiting for a date.
Room Additions & Second Story Additions
A room addition in Martinez runs $45,000 to $130,000, and a second story usually lands in the upper half of that range, because the existing structure has to carry the load. On the pre-1920 bungalows near downtown, that often means foundation work before framing work. We’ll tell you that on the first visit, not when the walls are already open.
What happens when you call
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A real person answersNo phone trees - you reach a local pro.
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You get an upfront price rangeHonest numbers before anyone is dispatched.
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A background-checked tech heads outLicensed & insured, dispatched right away.
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You approve before work beginsNothing starts until you say go.
Trusted Brands We Service in Martinez
We carry premium materials across every trade, because the salt air in Martinez punishes generic stock. That means GAF on the roof, where the sustained delta winds demand fasteners and underlayment rated for uplift – and it means Schluter in wet areas, where the marine humidity never fully leaves the walls. We also stand behind Grohe and Sterling in bathrooms, because the customers we serve in Martinez want fixtures they can look up, not mystery brands off a van. If something fails, the 90-Day Done Right Promise means one call brings Tom back.
Common Home Additions & ADU Problems We See in Martinez Homes
- Unreinforced foundations on adobe clay: The pre-1920 homes near downtown Martinez were never bolted to their mudsills, and the clay beneath pushes hard enough to crack new addition walls within two years. We stabilize and relevel before framing begins.
- Rusted hardware in the marine air: Standard galvanized window frames and railing hardware corrode and seize near the strait, leaving rust streaks and failed seals by year eight. We spec hot-dip galvanized or stainless on every exterior connection.
- Heaving paver patios and walkways: Sand-only joints on expansive clay expand and contract with every wet-dry cycle, so patios separate and heave within a few winters. We use compacted base and sealed joints that move with the ground.
- Hidden knob-and-tube and undersized framing: Older Martinez homes with original lath-and-plaster walls often carry electrical and structural surprises that no permit inspector wants to sign off on. We open walls only after the scope is on paper, so the surprise is a line item, not a bill at the door.
Pricing for Home Additions & ADU in Martinez, CA
Here’s what we quote in Martinez, and these numbers hold across our jobs in the 94553 ZIP:
| Project Type | Typical Range |
|---|---|
| Home Addition | $45,000 - $130,000 |
| ADU Construction | $90,000 - $220,000 |
| Garage Conversion | $30,000 - $80,000 |
The Martinez premium over the same plan in Concord or Pleasant Hill comes down to materials: the coastal-spec fasteners, marine-grade finishes, and foundation stabilization that the strait wind and clay demand. The inland-spec version of the same job looks cheaper on paper and fails within a decade. We don’t sell that version. Call (877) 610-1318 for a free estimate – it comes in writing, with every allowance and every line item priced before you sign anything.
We Also Serve Cities Near Martinez
Most of our Martinez customers come from Pleasant Hill, Contra Costa Centre, Waldon, and Benicia, and we bring the same coastal-spec approach to every one. If you’re in one of those towns and weighing an addition or ADU, our Home Additions & ADU in Martinez team covers the whole corridor – same pricing discipline, same written change orders, same 90-Day Done Right Promise.
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 - Home Additions & ADU in Martinez
Yes, and we’ll tell you that before anyone picks up a hammer. The pre-1920 wood-frame homes in downtown Martinez and the surrounding hillside neighborhoods were built without anchor bolts tying the mudsill to the foundation, and the expansive adobe clay underneath has spent a century pushing those foundations around. If we set new walls on an unreinforced perimeter, you’ll see cracks in the drywall within two years. We stabilize, bolt, and relevel first – and that scope goes on paper before framing starts. Call (877) 610-1318 for an exact assessment of your foundation.
Because the salt air and the sustained delta wind off the Carquinez Strait force a materials spec that an inland city doesn’t require. Our ADU jobs in Martinez use hot-dip galvanized or stainless fasteners on every exterior connection, marine-grade window frames, and roof assemblies rated for wind uplift that would be over-spec in Concord. Plus the clay on the hillside lots demands a foundation design that an inland slab doesn’t need. The materials cost more, and skipping them costs more. Call (877) 610-1318 and we’ll show you the line-item difference on paper.
We pull every permit and sit through every inspection, because the historic district review adds a layer that an out-of-town crew will treat as optional – and it isn’t. The city reviews anything visible from the street, which often means the exterior elevation, window proportions, and materials get scrutiny. We write the scope around what Martinez will actually approve, and we don’t start work until the permit is in hand. The permit inspector works for you, not for us.
Foundation stabilization, almost always. On the older blocks near downtown Martinez, we regularly find perimeters that were never bolted to their mudsills, with clay that has pushed the concrete out of level. Sistering joists and releveling floors becomes expected scope before any visible remodel work begins – and if nobody told you that upfront, you’ll see it as a surprise invoice at the end. We put it in the estimate before we start, so it’s a line item, not a shock. Call (877) 610-1318 for a free estimate that includes the foundation work you’ll actually need.
Sometimes, but only after we engineer what’s under it. A pier-and-beam foundation on Martinez clay moves seasonally, and adding a second story means the existing piers and beams have to carry a load they were never designed for. We’ve framed second-story additions over original 1910 bungalows near the historic district, and in each case the first step was stabilizing and releveling the structure below before any load-bearing walls went up. If the existing system can’t be brought up to code, we’ll tell you – and we’ll tell you in writing. Call (877) 610-1318 to schedule a structural walkthrough.
If you’re weighing an addition or an ADU in Martinez – whether it’s a room over a 1910 bungalow on the hillside or a detached unit in the flats – start with a free estimate. Call (877) 610-1318 and ask for Tom or one of his sons. We’ll walk the lot, check the foundation, and price the work for this city’s wind and clay – not for a generic inland template.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Martinez and the surrounding Contra Costa County communities.