An ADU in Redwood City is one of the Peninsula's more attainable backyard investments: lots in the flatland neighborhoods are generously sized by mid-Peninsula standards, the city has leaned into housing production, and rents driven by downtown's job growth and the tech corridor make the math work. Zen Construction, a licensed California General Contractor (CSLB #1041370) with 18 years and 140+ projects behind us, designs, permits, and builds ADUs as a single fixed-price package.
The honest first step is feasibility, not floor plans. Sewer depth, panel capacity, setbacks, and — in the hills — slope determine what your lot can actually carry. Book the free site assessment through our estimate page and we will tell you plainly whether your project pencils.
ADU Rules in Redwood City: State Floor, Local Details
California law sets the baseline the city cannot undercut: ministerial approval of complete applications on a 60-day clock, a guaranteed detached unit of up to 800 sq ft at 16 feet with 4-foot side and rear setbacks, and no discretionary design review. Redwood City has been comparatively proactive — the city publishes clear ADU guidance and processes applications through its Community Development Department without the friction some neighboring towns still generate.
Local details that shape design here: units above 800 sq ft follow the city's objective standards for the zone, and hillside parcels in Farm Hill and along the Emerald Hills boundary can involve grading review and, where the parcel is unincorporated, San Mateo County jurisdiction instead of the city's. We resolve the jurisdiction question in feasibility, because the two paths have different paperwork and timelines.
Garage Conversions, Backyard Cottages, and JADUs Across the City
The flatland neighborhoods — Friendly Acres, Centennial, Woodside Plaza — are classic garage-conversion territory: detached single or double garages on the rear of the lot, already served by a driveway, converting to studios and one-bedrooms from around $120k. Mount Carmel's deeper prewar lots often take a detached new-build cottage of 600–1,000 sq ft while keeping real yard space. In Farm Hill, slope drives the design: stepped foundations and retaining work cost more but often buy a unit with a view.
Redwood Shores is the exception in the portfolio — HOA-governed planned developments there mean state ADU law still applies, but CC&R coordination and tight lot coverage make JADUs or interior conversions the realistic path more often than backyard construction. A JADU of up to 500 sq ft inside the existing house, with its own entrance and efficiency kitchen, remains the lowest-cost route anywhere in the city and can be paired with a detached unit on the same lot.
The Investment Case for a Redwood City ADU
Typical costs: garage conversions from about $120k; detached new-build ADUs in the Bay Area run $250k–450k depending on size and site, and most Redwood City flatland projects land in the low-to-middle part of that range — one of the better cost positions on the Peninsula, since utility runs are short on these lots and grading is minimal outside the hills. Units under 750 sq ft avoid development impact fees under state law.
On the income side, downtown Redwood City's office and biotech growth plus Stanford and Meta commuters keep one-bedroom rents strong, and small units lease fast. Several of our clients house family in the ADU first and convert to rental later — the design decisions differ slightly, and it is worth telling us the real plan up front. Financing is available for construction if you prefer not to fund from equity.
One Contract from Feasibility to Final Inspection
You hire one company. We start with the site: locate the sewer lateral and measure its depth, load-check the electrical panel, map setbacks and trees, and confirm city versus county jurisdiction. Design follows — plans, structural engineering, Title 24 — with a free AI visualization at /design if you want to see a cottage rendered into a photo of your actual backyard. We submit, run the plan check, and mobilize our own crews the week the permit issues.
Construction on a detached unit typically takes four to six months; garage conversions run faster. You get weekly photo updates, scheduled city inspections, and a closed permit at the end — plus a unit that was priced completely at contract, including the trenching and panel work that other bids conveniently leave out.
Why Build Your Redwood City ADU with Zen Construction
Because ADU budgets die in the ground, not in the framing. We measure sewer depth before quoting, not after excavating. We know which Redwood City submittal details prevent a second plan-check round, and when a parcel turns out to be county land we already know that counter too. Our crews built the projects in our portfolio themselves — the same people will build yours.
- CSLB #1041370, licensed and insured, 18 years in business
- Fixed price covering site work, not just the box
- Plans, Title 24, structural engineering, and permits in-house
- Own construction crews; weekly photo updates
- Financing available
Neighborhoods we serve in Redwood City
Around Redwood City we build to the lot: garage conversions in Friendly Acres and Centennial where detached garages sit ready on the rear lot line, new backyard cottages on the deep parcels of Mount Carmel and Woodside Plaza, engineered hillside units in Farm Hill and on the Emerald Hills edge where county jurisdiction sometimes applies, and JADU conversions in Redwood Shores homes governed by HOA covenants.
Reviews from Redwood City and nearby
Uploaded a photo half expecting a gimmick. Got back my own kitchen in warm greige with black hardware, showed my husband, and that ended the debate. The install came out close to the picture.
Two bathrooms and the kitchen in one go. Same crew the whole time, same foreman answering my texts. We stayed in the house and it was livable — dust barriers up every morning, floors covered.
Coastal kitchen built around the big window we refused to give up. They redesigned for the light instead of building over it — open shelving, quartz, tile to the ceiling. I still take pictures of it.
Recent work you can price
$15,000 – $25,000
$18,000 – $30,000
$22,000 – $36,000
ADU Construction in Redwood City — FAQ
How fast does Redwood City approve ADUs?
State law caps review of a complete application at 60 days, and Redwood City's Community Development Department generally runs the process smoothly by Peninsula standards. Incomplete submittals are what burn time — missing structural sheets or energy forms restart the clock. Our full-package submittals typically clear in one or two review rounds, and we answer every comment ourselves.
What does an ADU cost in Redwood City?
Garage conversions start around $120k. Detached new builds run $250k–450k across the Bay Area, and flatland Redwood City lots usually land low-to-middle in that range thanks to short utility runs and easy access. Hillside sites in Farm Hill add foundation and grading cost. We quote a fixed price after the free feasibility visit, with site work included.
Can I convert my detached garage into a rental unit?
In most Redwood City neighborhoods, yes — detached garages in Friendly Acres, Centennial, and Woodside Plaza convert well, and the city cannot require you to replace the lost parking in most cases under state law. The usual scope is foundation checks, insulation, a bathroom and kitchenette, fire separation, and an upgraded electrical feed. Most conversions finish in two to three months of construction.
My lot slopes — can I still build an ADU in Farm Hill?
Usually yes, with engineering. Sloped parcels take stepped or pier foundations and sometimes retaining walls, which raises cost but rarely kills feasibility. Parcels on the Emerald Hills side may fall under San Mateo County jurisdiction rather than the city, which changes the permit path. We confirm jurisdiction and rough grading scope during the free site assessment before you spend on design.
Do Redwood Shores HOA rules block ADUs?
They cannot outright ban them — state law voids covenants that prohibit ADUs — but CC&Rs can impose reasonable restrictions, and lot coverage in Redwood Shores is tight. In practice, interior conversions and JADUs are often the workable route there. We review your CC&Rs during feasibility and design a unit that clears both the city and the association.
Is a JADU worth it compared to a full ADU?
If budget is the constraint, often yes. A JADU converts up to 500 sq ft of the existing house — commonly a bedroom wing or oversized garage bay — with a separate entrance and efficiency kitchen, at a fraction of new-build cost. Income is lower than a detached unit but so is risk, and state law allows adding a detached ADU later on the same lot.