Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
Before
After
Before
After
Before
AfterFast, Reliable Home Additions & ADU Across Redwood City
A typical home addition in Redwood City runs $45,000-$130,000, while a full detached ADU construction project runs $90,000-$220,000. Most Redwood City projects move from signed contract to permit pull in four to eight weeks, depending on San Mateo County plan-check queue depth and whether geotechnical review is required. Call (650) 560-7228 to schedule your free estimate.
We’ve worked the full span of Redwood City’s housing stock, from pre-1940 Victorians near Broadway to 1970s ranch homes in Farm Hill to the bay-fill subdivisions of Redwood Shores. Our crews are dispatched from our San Francisco Bay Area office, and we coordinate permits, inspections, and material deliveries specifically for Redwood City’s San Mateo County jurisdiction. That local fluency matters when a project hits the county’s Title 24 energy compliance checks or triggers a mandatory geotechnical review on the east side of town.
Why Rowan Construction Group Redwood City Is Redwood City’s Preferred Home Additions & ADU Company
Rowan Construction Group has delivered more than 4,000 projects since 2007, every one with a written price before work started and a documented photo record when the crew left. In Redwood City specifically, we’ve built second-story additions over original 1950s ranch construction, converted detached garages to ADUs near Sequoia Station, and navigated the geotechnical review process for new detached ADUs in Redwood Shores. Our 365-Day Done Right Promise is printed on every contract page, backed by a terms page, not an asterisk.
Our customers in Redwood City, Menlo Park, and San Carlos research contractors the way they research appliances - they read the three-star reviews and want the price range on the page before they make contact. We put it there. Under Clause 1 of the Haven Standard, the price is written before anyone starts. No “call for a quote.” A flat price, a written scope, and a written warranty.
Calls are answered by a live person 24/7. Our technicians are background-checked and uniformed, and every visit includes a documented photo record as standard - not an upgrade. We also offer a Free Second Opinion on any written estimate: bring a competitor’s quote and we’ll review it line by line at no charge.
Our Home Additions & ADU Services in Redwood City
ADU Design & Permitting
ADU design and permitting in Redwood City means navigating San Mateo County’s specific setback, height, and parking requirements, plus the city’s local ADU ordinance that aligns with but does not duplicate state law. We handle the full package: site survey, floor plans, structural calcs, energy compliance, and permit submission. In Redwood Shores, we flag geotechnical review early so it doesn’t stall the plan-check queue. A typical garage conversion ADU in Redwood City runs $30,000-$80,000; a new detached ADU runs $90,000-$220,000. Both are quoted as flat prices with written scope before any work starts.
Garage Conversion ADU
Garage conversions are the fastest path to rental income or multigenerational housing in Redwood City, especially in the central flatlands where 1945-1965 ranch homes dominate and detached garages are common. The catch: these older garages often have slab-on-grade foundations with no footing depth, no insulation, and electrical service sized for a door opener, not a dwelling unit. We inspect the slab, the framing, and the utility capacity before we quote. If the slab won’t carry a conditioned space, we price the replacement in writing as a separate line item, approved before we touch it.
New Detached ADU
New detached ADUs in Redwood City range from compact studio units to two-bedroom structures with full kitchens. In Redwood Shores, the bay-mud substrate drives foundation design - spread footings or pier systems that a Belmont or San Carlos job would never need. In Emerald Hills and Farm Hill, hillside grading and drainage are the critical variables. We coordinate the geotechnical report, the structural engineering, and the Title 24 energy modeling as a single workflow so the permit application is complete the first time.
Junior ADU & Interior Conversion
Junior ADUs - converted interior space within an existing home, with a separate entrance and efficiency kitchen - work well in Redwood City’s older neighborhoods where lot coverage limits block a detached unit. We’ve converted basement storage rooms in downtown-adjacent Victorians and partitioned off portions of 1960s ranch floor plans near Woodside Road. The constraint is usually the existing electrical panel and the egress window requirement; we price both as line-item allowances in the written contract.
Second Story Additions
Second story additions are where Redwood City’s housing stock shows its age. We opened up a 1950s ranch in the Farm Hill neighborhood for a second-story addition and found original wood-frame construction with an undersized load path and subfloor joists that had dried and shrunk from years of sun exposure. Our crew wrote an allowances line into the scope of work for subfloor repair and framing upgrades, priced the geotechnical review and shoring depth separately, and had it approved in writing before we pulled the permits. The crew sheathed and weather-sealed the open structure over the weekend so the family could still use the lower level until inspection sign-off on the new rough-in.
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.
Before
AfterTrusted Brands We Service in Redwood City
We source across fifty-plus vetted brands, which lets us put honest numbers in the written quote rather than inflated allowances. For window packages in Redwood City ADUs and additions, we regularly specify ES Windows and ECO Window Systems for their Title 24 compliance ratings and local distributor availability. For structural and finish hardware, CGI products are stocked through our Bay Area supply chain with turnaround times that keep Redwood City projects on schedule. We don’t list brands to impress; we name them so the customer knows what they’re paying for and can compare spec-for-spec against any other quote.
Common Home Additions & ADU Problems We See in Redwood City Homes
- Bay-mud excavation surprises in Redwood Shores. Our crew hits soft bay mud just inches below grade during footing or drainage trench excavation, forcing on-the-fly shoring-depth and bearing-capacity decisions that a San Carlos or Menlo Park job site never triggers. We price geotechnical review and contingency shoring as a written allowance before we break ground.
- Aged framing and subfloor in pre-1940 downtown homes. In the Victorian and craftsman homes near Broadway and Middlefield, opening walls for an addition often reveals original wood-frame construction with aged subfloor systems and undersized load paths, driving unanticipated framing and code-upgrade costs. We inspect and photograph the structure before demolition, then write the repair scope as a signed change order if needed.
- Expansive clay movement in Emerald Hills and Farm Hill. Redwood City’s coastal fog gap makes it measurably warmer and sunnier than neighboring San Mateo or Menlo Park, intensifying summer soil-drying cycles in the hillside neighborhoods. We see foundation drainage failures and slab heave that fog-belt cities to the north rarely face, so we specify deeper footing drains and moisture barriers as standard in these zones.
- Permit-triggered code upgrades on older homes. Once walls are open, Redwood City’s building department requires current electrical, plumbing, and energy code compliance in the affected area - not just the new addition. We identify the likely upgrade scope during pre-construction inspection and write it into the base contract, not as a surprise add-on.
Pricing for Home Additions & ADU in Redwood City, CA
Home additions and ADUs in Redwood City are quoted as flat prices with written scope before any work starts. The table below shows our current ranges for the three most common project types. Every quote includes the documented photo record, the written warranty, and the 365-Day Done Right Promise.
| Project Type | Price Range in Redwood City |
|---|---|
| Home Addition (room addition, bump-out, or second story) | $45,000 - $130,000 |
| ADU Construction (new detached unit) | $90,000 - $220,000 |
| Garage Conversion ADU | $30,000 - $80,000 |
What moves the number: foundation type and depth, especially in Redwood Shores; structural framing condition in pre-1940 homes; electrical service upgrade requirements; and the extent of permit-triggered code upgrades. We do not proceed on any change until the change order is signed - the administrative discipline Haven acquired Rowan for, and the reason our projects finish within a few percent of the agreed price. Call (650) 560-7228 for an exact quote - estimates are free.
We Also Serve Cities Near Redwood City
Our Home Additions & ADU crews work across the mid-Peninsula, including Redwood City and the surrounding communities of Menlo Park, San Carlos, Palo Alto, and Belmont. Each city has its own permit jurisdiction and soil conditions; we quote and permit accordingly.
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. Redwood Shores sits on reclaimed Cargill salt-pond bay fill, and San Mateo County requires geotechnical review for any structural addition or new foundation work in that zone. We coordinate the report as part of our permit package and price it as a separate line item in the written quote. Call (650) 560-7228 for an exact quote - estimates are free.
Pre-1940 Victorians and craftsmans downtown, and 1945-1965 ranch homes on the flatlands, were built with original wood-frame construction and subfloor systems that were never designed for modern load paths or open floor plans. Decades of Redwood City’s fog-gap sun exposure dries and shrinks the joists. We inspect and photograph the structure before demolition, write repair allowances into the contract, and price any needed upgrades in a signed change order before we cut. Call (650) 560-7228 for an exact quote - estimates are free.
Redwood City’s coastal fog gap makes it warmer and sunnier than San Mateo or Menlo Park, which intensifies summer soil-drying cycles in the Emerald Hills and Farm Hill hillside neighborhoods. That drying triggers expansive-clay soil movement and foundation drainage failures that fog-belt cities rarely face. We specify deeper perimeter drains and moisture barriers as standard in these zones, priced into the base contract. Call (650) 560-7228 for an exact quote - estimates are free.
The permit triggers San Mateo County inspections at rough-in and final, ensures code compliance for structural, electrical, plumbing, and energy requirements, and creates a documented record that protects your property value and insurance coverage. It also means any work behind walls must meet current code, not just the code when the house was built. We pull the permit, schedule the inspections, and pass them - included in our flat price. Call (650) 560-7228 for an exact quote - estimates are free.
We inspect before we quote, write allowances for likely surprises into the base contract, and require a signed change order before any unpriced work proceeds. Under the Haven Standard, Clause 1 is the written price before anyone starts, and no change proceeds without documentation. Our projects finish within a few percent of the agreed price because the discipline is administrative, not aspirational. Call (650) 560-7228 for an exact quote - estimates are free.
Ready to add space to your Redwood City home? Call (650) 560-7228 to schedule your free estimate. We’ll review your property, identify the specific conditions your project will face - whether bay-mud review in Redwood Shores, aged framing downtown, or hillside drainage in Emerald Hills - and deliver a flat written price with a written scope and warranty before anyone picks up a tool.
Written by Grant Rowan, Owner at Rowan Construction Group, serving Redwood City since 2007.