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AfterFast, Reliable Home Additions & ADU Across Redwood City
A typical home addition or ADU in Redwood City runs $45,000-$130,000 for room additions and $90,000-$220,000 for detached ADUs, with most projects taking 3-6 months from permit to final inspection. Call (669) 259-1843 to schedule your free estimate. Our crews serve Redwood City from our San Francisco Bay Area dispatch office, and we know the local permit cycle, the all-electric reach code, and the tight-lot logistics that out-of-area contractors underestimate.
We’ve worked on pre-WWII craftsman bungalows near the historic downtown, 1950s ranch homes on the flatlands, and engineered-fill parcels in Redwood Shores. Each neighborhood brings its own foundation type, setback rule, and access constraint. We account for all of it in the written quote before anyone picks up a tool.
Why Rowan Construction Group Santa Clara Is Redwood City’s Preferred Home Additions & ADU Company
Our Home Additions & ADU team has delivered 4,000-plus projects since 2007, every one with a written flat price before work started and a documented photo record when the crew left. In Redwood City specifically, we’ve learned that the difference between a project that finishes on budget and one that doesn’t is usually the pre-construction site survey, not the framing skill.
Redwood City homeowners research contractors the way they research appliances. They read the three-star reviews, and they want the price range on the page before they make contact. We put the number in writing. Under Clause 1 of The Haven Standard, the price is written before anyone starts. No “call for a quote” here.
Our crews are background-checked and uniformed. A live person answers calls 24/7. Every visit includes a documented photo record as standard, not an upgrade. And our 365-Day Done Right Promise is printed on every page, backed by a terms page, not an asterisk.
We coordinate dispatch and scheduling from our San Francisco Bay Area office, with crews serving Redwood City locally. That means we understand the San Mateo County permit workflow, the Redwood City planning counter’s current review timeline, and the all-electric reach code that has been mandatory for new construction and major additions since 2019.
Our Home Additions & ADU Services in Redwood City
Second Story Additions
Second story additions in Redwood City are common on the pre-WWII craftsman bungalows and 1950s ranch homes that dominate the flatlands. The structural challenge is usually the existing foundation: pre-war wood-frame cripple walls need seismic retrofit before they carry a second floor, and 1950s slab-on-grade ranches often require grade-beam augmentation. On a project near the historic downtown, we pulled permits for a second-story addition on a lot so tight the only lay-down area was the driveway; we staged materials in a rolling pod, hand-carried the structural steel through a side yard under 5 feet wide, and posted 10-day party-wall notice to the neighbor sharing the east wall before our engineer cut in the new load-bearing beam. Because the house sits on a pre-war wood-frame foundation and the new all-electric reach code required a 200-amp panel upgrade with an EV-ready subpanel, our electrician roughed the new subfloor circuits while the framing crew was still on the joists - keeping the city inspection sign-offs on consecutive days. A second story addition in Redwood City typically runs $45,000-$130,000.
New Detached ADU
New detached ADUs in Redwood City face the tightest lot constraints on the Peninsula. Setbacks on 5,000-square-foot parcels often leave a buildable footprint of just 400-600 square feet, which means every design decision carries cost weight: a flat roof saves height but needs a membrane rated for ponding; a shed roof buys headroom but complicates the ridge-line aesthetic review in some neighborhoods. In Redwood Shores, the engineered fill over bay mud requires deep foundations or helical piers that add $8,000-$15,000 to the base cost before framing begins. The all-electric reach code means no gas meter, no furnace, no tankless water heater - so the panel upgrade and EV-ready subpanel are written into our scope before we submit plans. A new detached ADU in Redwood City typically runs $90,000-$220,000.
Room Additions
Room additions - a master suite off the back, a family room bump-out, a home office wing - are the most common project type we quote in Redwood City. The flatlands ranch homes have the easiest access and the most predictable foundations; the hillside parcels west of El Camino Real need retaining-wall coordination and often trigger geotechnical review. Every room addition quote we write includes a line item for access and staging, because Redwood City’s narrow side yards, no-alley lots, and permitted street parking create hand-carry labor and permit parking variances that blow allowances before framing is done. We measure the side yard, check the curb cut, and price the logistics - not guess at them.
Garage Conversion ADU
Garage conversions are the fastest path to rental income in Redwood City, but they carry specific local traps. A garage conversion under 750 square feet can often use the state’s streamlined ADU process, but San Mateo County still requires the all-electric conversion: no extending the gas line to a new kitchen or bathroom. The slab is usually uninsulated and may need a moisture barrier retrofit, especially on bay-adjacent parcels where the groundwater table sits high. And if the garage shares a wall with the main house, the party-wall notice and fire-separation detailing are permit-critical. A garage conversion ADU in Redwood City typically runs $30,000-$80,000.
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.
Before
AfterTrusted Brands We Service in Redwood City
We source across fifty-plus vetted brands, giving the written quote honest numbers rather than inflated ones. For Redwood City ADU and addition projects, we regularly specify Belgard pavers for courtyard hardscaping on tight-lot sites where yard space is minimal and every square foot needs to earn its keep. We also work with Bufftech vinyl fencing for privacy screens on zero-lot-line parcels, and ActiveYards aluminum systems where coastal exposure near Redwood Shores demands corrosion resistance. Our material orders are staged through local suppliers with Redwood City delivery routes, which keeps lead times short and lets us hold to the written schedule.
Common Home Additions & ADU Problems We See in Redwood City Homes
- Underestimating access and staging costs on a tight lot. Narrow side yards under 6 feet, no alley access, and permitted street parking zones create hand-carry labor and permit parking variances that blow the allowances before framing is done. We measure every access path during the site survey and write the cost into the quote.
- Missing the San Mateo County all-electric reach code on a major addition. Gas rough-in triggers a plan-check rejection and a change order for panel upgrade and EV-ready subpanel. We coordinate our electrician and structural engineer before submission so the 200-amp service and subpanel locations are on the first set of plans.
- Skipping party-wall notice or historic/overlay review on downtown-adjacent parcels. A neighbor complaint or design-review hold can shut the site down mid rough-in. We post 10-day notice and pull the historic resource preliminary review before the permit application, not after.
- Foundation surprises on Redwood Shores engineered fill. The bay mud and former Cargill salt pond fill underlying Redwood Shores compresses under load and liquefies in seismic events. We flag geotechnical report requirements in our initial scope letter, not in a change order after the first shovel.
Pricing for Home Additions & ADU in Redwood City, CA
Every project is quoted with a flat written price and written scope before work begins. No change proceeds without a signed change order. This is the discipline that has kept our projects within a few percent of the agreed cost across 4,000-plus jobs.
| Service | Redwood City Price Range |
|---|---|
| Home Addition (room addition, second story) | $45,000-$130,000 |
| ADU Construction (new detached) | $90,000-$220,000 |
| Garage Conversion ADU | $30,000-$80,000 |
What moves the number within these ranges: foundation type (slab, cripple wall, or engineered fill), electrical service upgrade requirements, access and staging complexity, and whether geotechnical or structural engineering is required. We deliver the written quote with line-item breakdowns, not a single lump sum. Bring a competitor’s written estimate and we’ll review it line by line at no charge - our Free Second Opinion.
Call (669) 259-1843 for your free estimate. The price is written before any work starts, every time.
We Also Serve Cities Near Redwood City
Our Home Additions & ADU in Redwood City crews also work in Menlo Park, San Carlos, Palo Alto, and Los Altos. Each city has its own permit workflow and code interpretation; we maintain separate file folders for each planning counter because a Menlo Park ADU submission and a Redwood City ADU submission follow different review tracks even under the same state law.
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
Yes. San Mateo County’s reach code mandates all-electric new construction and major additions, with no gas rough-in permitted. This means a panel upgrade and EV-ready subpanel coordination are standard line items on nearly every residential project in Redwood City, a workflow quirk that still catches out-of-area subs unfamiliar with the local ordinance. Our electricians coordinate with our structural engineers before plan submission so the service upgrade is drawn into the first set of plans, not added later. Call (669) 259-1843 for an exact quote - estimates are free.
You need a 10-day party-wall notice posted to the adjoining owner before structural work begins, and your engineer’s drawings must detail the fire separation and structural independence of the shared wall. In Redwood City’s historic downtown and adjacent neighborhoods, some parcels also trigger design review or historic resource preliminary review, which adds 2-4 weeks before permit submission. We handle the notice posting and the neighbor coordination as part of our pre-construction scope. Call (669) 259-1843 for an exact quote - estimates are free.
A tight lot adds access and staging line items that flatland contractors in less dense markets rarely encounter: rolling material pods instead of lay-down yards, hand-carry labor through side yards under 5 feet wide, and permit parking variances for the construction vehicle footprint. On Redwood City lots with no alley and narrow side yards, these logistics can add 8-15% to the base construction cost. We measure every access path during the site survey and write the cost into the quote, not discover it during framing. Call (669) 259-1843 for an exact quote - estimates are free.
Most likely yes. Redwood Shores is built on engineered fill over compressible bay mud and former Cargill salt pond fill, which requires liquefaction mitigation and often deep foundations or helical piers. San Mateo County typically requires a geotechnical report for any new detached structure in the 94065 zip, and Redwood City’s building counter will flag it at plan check if it’s missing. We include the geotechnical scope letter in our initial proposal so the report cost is in the written price, not a surprise change order. Call (669) 259-1843 for an exact quote - estimates are free.
Streamlined ADUs under 750 square feet typically clear in 60-90 days if the plans are complete and no historic review is triggered. Room additions and second stories run 90-120 days, with second stories on pre-war foundations often needing a structural plan check that adds 2-3 weeks. The all-electric reach code means electrical plan check happens in parallel with structural, not sequential, which saves time if the panel upgrade is drawn correctly the first time. Our permit expeditor tracks each submittal weekly. Call (669) 259-1843 for an exact quote - estimates are free.
Ready to price your project? Call (669) 259-1843 to schedule your free estimate. We’ll deliver a written flat price with a written scope and a written warranty before any work starts. That’s Clause 1 of The Haven Standard, and it’s how we’ve kept projects within a few percent of the agreed cost since 2007.
Written by Grant Rowan, Owner at Rowan Construction Group, serving Redwood City since 2007.