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 Redwood City
Home additions and ADUs in Redwood City typically run $45,000 to $130,000 for a room addition and $90,000 to $220,000 for a full detached ADU, and the single biggest variable is what’s under your house. Redwood City is two different towns from a builder’s perspective: the flatland ranches of 94063 and 94061 sit on conventional Peninsula soil, while Redwood Shores in 94065 sits on filled bay mud that settles and shifts for decades. That split drives foundation costs more than anything else, and if your contractor doesn’t know it, you’ll find out the hard way. We’re Barrett & Sons Construction, Tom Barrett’s crew, and we’ve been opening Redwood City walls long enough to know what’s behind them before the first stud comes out. Call (877) 610-1318 and we’ll walk your lot, check your foundation, and put real numbers in writing.
Why Barrett & Sons Construction Is Redwood City’s Preferred Home Additions & ADU Company
Tom Barrett founded this company in 1998, and his sons run crews on Redwood City jobs every week. That matters because when you call about a change order or a question mid-project, the person who picks up has actually been inside your house. Not a call center. Not a rotating project manager. The Barretts live twenty minutes away, and if something isn’t right, they want to hear about it before the inspector does.
Our Home Additions & ADU work in Redwood City gets the same treatment on every job: permits pulled before work starts, inspections signed before payment is requested, and every price change delivered as a written change order with your signature on it. The allowance that isn’t on paper is a surprise waiting for a date. That’s how we’ve kept a strong local reputation across 94063, 94061, 94064, and 94065 for over 29 years, and it’s why homeowners in Redwood Shores, Woodside Plaza, and the Roosevelt neighborhood call us back for their second project.
Ask anyone on your street, or look up Tom Barrett’s license number yourself. He publishes his name, his address, and his license on every estimate. The permit inspector works for you, not for us, and that’s exactly how we like it.
Our Home Additions & ADU Services in Redwood City
ADU Design & Permitting
An ADU in Redwood City means meeting California’s ADU statutes plus San Mateo County and city-specific setback, height, and fire-sprinkler requirements, and the rules changed again recently. We handle the full design and permit package: site plan, structural drawings, Title 24 energy calcs, and the submittal package the city actually wants to see. A standard ADU permit set in Redwood City takes roughly four to eight weeks depending on plan-check backlog, and we flag likely plan-check comments before submission so your timeline doesn’t stall on a missing geotech letter. If your lot’s in 94065, that geotech review is not optional, and we order it before we even draw the foundation.
New Detached ADU
A new detached ADU in Redwood City runs $90,000 to $220,000 depending on size, finish level, and what’s under the ground. On flatland lots in 94061 and 94063, a standard slab or shallow footing often works. In Redwood Shores, where the bay mud compresses under load, expect deep piers or pile-supported footings, and expect the plan checker to require a soils report. It adds cost, but it’s the difference between a building that stays square and one that cracks its drywall in five years. We build the foundation for where you are, not where a generic ADU plan was drawn.
Garage Conversion ADU
Converting a garage in Redwood City lands between $30,000 and $80,000, and the condition of your existing slab and framing drives a lot of that number. Many 1940s and 1950s garages in 94063 were built as uninsulated shells with shallow footings and no vapor barrier, so a conversion means lifting floor framing, adding insulation, and sometimes pouring a new slab. In Redwood Shores, older garage slabs have settled right along with the house; we’ve re-leveled more than a few before framing interior walls. A garage conversion ADU still needs its own permit, its own subpanel, and its own energy compliance, which we handle start to finish.
Junior ADU & Interior Conversion
A junior ADU, or JADU, is the fastest path to rentable square footage in Redwood City, and state law makes them hard for cities to deny. Typically it’s an interior conversion: taking an existing bedroom or bonus room and adding an efficiency kitchen and a bathroom. Redwood City’s older ranch homes often have a den or a bedroom sitting right next to an underused bathroom, which makes the plumbing work simpler than building from new. We pull the permit, upgrade the subpanel if the added load requires it, and write every allowance into the contract in plain English.
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 Redwood City
When you’re adding square footage or building an ADU in Redwood City, the windows and exterior doors matter more than people think. Coastal air off the Bay in 94065 eats standard flashing faster than spec allows, and summer heat in the flatlands punishes cheap glass. We install Simonton, Ply Gem, and PGT windows and doors on additions and ADUs across Redwood City, and we keep local stock on hand for common sizes so a three-week window lead time doesn’t become an eight-week stall. These are brands you can look up, with warranties the manufacturer actually honors, not mystery units off a van.
Common Home Additions & ADU Problems We See in Redwood City Homes
- Out-of-plane slabs in Redwood Shores. Bay mud settles unevenly for decades, and we’ve measured 1980s slabs in 94065 out of level by over an inch. Framing an addition on that without foundation remediation guarantees cracked walls and binding doors within two years.
- Undersized 1940s-era subpanels in the flatlands. A 1950s ranch in 94063 often has a 60-amp panel feeding the whole house, and an ADU or room addition will overload it. The city catches it during plan review, and it becomes a line item on the permit. Better to know before you sign.
- Knob-and-tube and cloth-insulated wiring inside finished walls. We open a wall in an older Redwood City home for a room addition and find wiring that was code when Eisenhower was president. Once the wall’s open, the inspector requires it brought to current code. That’s a change order, and we write it before we touch it.
- Salt-air corrosion on bayfront homes. Redwood Shores properties face persistent salt-laden air that corrodes standard Simpson ties, metal flashing, and HVAC components faster than manufacturer specs assume. We spec stainless or heavy-gauge galvanized on exposed connectors in 94065, and the inspector signs off because we did.
Pricing for Home Additions & ADU in Redwood City, CA
Here are real Redwood City numbers, not national averages. These reflect what we see across 94063, 94061, 94064, and 94065 after accounting for local permit fees, soils conditions, and the cost of bringing older framing and electrical up to code once walls are open.
| Project Type | Typical Redwood City Range |
|---|---|
| Home Addition | $45,000-$130,000 |
| ADU Construction | $90,000-$220,000 |
| Garage Conversion | $30,000-$80,000 |
What moves the number: foundation conditions, especially in Redwood Shores where pile-supported footings may be required; electrical service capacity, because older panels often can’t carry the added load; whether the permit triggers sewer lateral replacement or fire sprinklers; and finish level, because KraftMaid cabinets and Cambria countertops cost more than stock units and last longer. Every line item goes in writing before work starts. No surprises, no phone-call pricing. Call (877) 610-1318 for a free, written estimate with your actual allowance schedule.
We Also Serve Cities Near Redwood City
Our crews are based out of the San Francisco Bay Area and work throughout the Peninsula, so if you’re in Redwood City or just over the line in San Carlos, Woodside, Menlo Park, or North Fair Oaks, you’ll get the same owner-operated crew and the same written change orders. Tom Barrett’s name is on the truck, wherever the job is.
Serving Redwood City, CA - Our Local Coverage Area
We’re based in the Redwood City 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 Redwood City
Because Redwood Shores is built on filled bay mud, not natural Peninsula soil, and that fill settles unevenly for decades after it’s placed. A significant structural project there typically requires a geotechnical report and deep piers or pile-supported footings to handle ongoing settlement and liquefaction exposure, which can add $15,000 to $40,000 or more to the foundation scope. One mile inland in downtown Redwood City, a standard slab or shallow footing on conventional soil is often fine. The difference isn’t our labor rate; it’s physics under the ground. Call (877) 610-1318 and we’ll tell you which category your lot falls into.
You’ll likely see requirements for electrical service upgrades, because many of those homes have 60-amp or 100-amp panels that can’t carry new loads; seismic anchoring if the perimeter foundation lacks bolts; smoke and carbon monoxide detection to current code; and possibly shear-wall retrofit on any wall we’re cutting into. In some cases we find ungrounded knob-and-tube or cloth-insulated wiring, which the inspector will flag the moment it’s visible. That’s why we write allowances into your contract up front, and any upgrade gets a written change order before we do the work. Call (877) 610-1318 to find out what your specific house is likely to require.
We stop and bring in a soils engineer. A slab that far out of plane means the fill beneath it is still moving, and adding framing on top of that will crack the structure within a few years. The fix usually involves driving pile-supported footings down to competent soil, then re-leveling the affected floor area before a single new stud goes up. It’s not cheap, but it’s the only way the inspector will sign off and the only way the building stays plumb. We’ve done it on more than a few Redwood Shores jobs, and we write the full remediation into a change order with your signature before we order materials.
You need a permit. Redwood City enforces building permits on ADUs and additions, and unpermitted work becomes a problem when you sell, refinance, or make an insurance claim. The city checks for unpermitted square footage against tax and permit records, and lenders often flag it. We pull permits on every eligible job, and the inspector works for you, not for us. That’s the whole point: the inspection protects your investment. Call (877) 610-1318 and we’ll handle the permit package from day one.
Redwood City sits in one of the sunniest, least-foggy microclimates on the Peninsula, which means fewer weather-related framing and roofing delays than you’ll see closer to the coast. That extends the viable outdoor construction season and makes Redwood City a strong candidate for room additions and detached ADUs almost year-round. Bayfront properties in Redwood Shores still get persistent salt air, which is a different problem, but rain delays are less common here than a few miles west. For a free estimate on your Redwood City addition or ADU, call (877) 610-1318.
Get Your Redwood City Home Addition or ADU Priced in Writing
You’ll get a written, line-item estimate with allowances shown, permits pulled, and every change order in writing before work proceeds. No surprise invoices, no allowance that isn’t on paper. We also honor four standing offers: $40 off any repair over $200, a free second opinion on any written estimate, no trip charge inside the county, and a permanent 10% senior and veteran discount. Call (877) 610-1318 to schedule your free estimate.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Redwood City since 1998.