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Before
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ADU construction in Redwood City typically costs between $90,000 and $220,000, depending on unit size, site conditions, and whether the ADU is a new detached structure or a conversion of existing space. Most homeowners in Redwood City land somewhere in the $130,000-$175,000 range for a fully permitted, move-in-ready detached ADU. That number includes design, permits, foundation, framing, mechanical systems, and finishes - not just the shell.
If you want a written price specific to your property before committing to anything, call (650) 560-7228. Under Clause 1 of the Haven Standard, a flat written price with a full written scope goes out before anyone picks up a tool.
ADU Construction Cost Breakdown (2026)
ADU construction in Redwood City costs $90,000-$220,000 depending on the type of unit you’re building. The table below shows how that range splits across the most common ADU types and the major cost categories within a project.
Cost by ADU Type
| ADU Type | Typical Cost Range (Redwood City) | Notes |
|---|---|---|
| Garage Conversion ADU | $30,000-$80,000 | Existing structure reduces framing and foundation cost; still requires full electrical, plumbing, HVAC, and insulation upgrades to meet Title 24 |
| Junior ADU (JADU, interior conversion) | $40,000-$90,000 | Carved from existing interior space; shared wall with main dwelling keeps structural costs lower |
| Detached ADU (400-600 sq ft) | $90,000-$145,000 | New foundation, framing, roof, and all MEP (mechanical, electrical, plumbing) runs from scratch |
| Detached ADU (600-850 sq ft) | $130,000-$180,000 | Most common size bracket for Redwood City lots; accounts for the majority of ADU projects we build |
| Detached ADU (850-1,200 sq ft) | $165,000-$220,000 | Larger footprint, often two-bedroom; may require upgraded utility service from PG&E |
Cost by Project Phase
| Phase / Line Item | Typical Cost Range |
|---|---|
| Architectural design and structural engineering | $6,000-$18,000 |
| Redwood City building permits and fees | $8,000-$22,000 |
| Site prep, grading, and foundation | $8,000-$28,000 |
| Framing and sheathing | $12,000-$30,000 |
| Roofing (GAF or Owens Corning shingles standard) | $5,000-$14,000 |
| Electrical rough-in and panel work | $6,000-$14,000 |
| Plumbing rough-in and fixtures (Kohler or Toto) | $7,000-$18,000 |
| HVAC (mini-split system is standard in RC) | $4,000-$10,000 |
| Insulation and Title 24 energy compliance | $3,000-$7,000 |
| Drywall, taping, and painting | $4,000-$9,000 |
| Kitchen cabinetry and countertops | $6,000-$20,000 |
| Bathroom tile, vanity, and shower | $5,000-$14,000 |
| Flooring | $3,000-$9,000 |
| Doors, windows, and exterior finishes | $5,000-$15,000 |
| Utility connections (water, sewer, electrical) | $4,000-$14,000 |
A few things push the final number toward the top of the range in Redwood City specifically. Permit fees through the Redwood City Building Division are on the higher end for San Mateo County – plan for $10,000-$22,000 in fees alone on a detached ADU, and budget extra time: first-plan-check cycles typically run 8-12 weeks, and a resubmittal adds another 4-6. Lot access in neighborhoods like Farm Hill, Emerald Hills, and parts of Edgewood can also add site-prep cost when a crane or special equipment is needed to move materials up a slope. On the other hand, a flat interior lot in Redwood Shores or near the Sequoia Station corridor tends to come in closer to the low-middle of the range.
Material costs in Redwood City reflect Bay Area supply chains and labor rates. Framing labor here runs roughly $12-$18 per square foot of framed area, compared to $8-$12 in the Central Valley. That gap is structural – it’s what local crews cost, and any quote that ignores it is a quote that will come back with change orders. At Rowan Construction Group, no change proceeds without a signed change order, which is how 4,000-plus projects since 2007 have finished within a few percent of the agreed price.
What Affects ADU Construction Pricing in Redwood City
- ADU type and existing structure condition. A garage conversion ADU in Redwood City costs $30,000-$80,000 because the shell is already standing. A detached unit on a bare lot costs $90,000-$220,000 because every element – from the foundation up – is built new. The condition of an existing garage matters too: if the slab is cracked, the framing is racked, or the roof decking is water-damaged, remediation gets added before conversion work even starts.
- Lot topography. Redwood City’s western neighborhoods – Emerald Hills, Farm Hill, and the streets climbing toward Edgewood Road – frequently have sloped lots that require either a stepped foundation, a deeper post-and-pier system, or significant grading. That work adds $8,000-$25,000 compared to a flat lot in the flatlands near Broadway or Veterans Boulevard.
- Permit and impact fees. San Mateo County’s infrastructure fees are embedded in Redwood City’s ADU permit costs. Expect to budget $8,000-$22,000 for permits, plan check, and school impact fees on a detached ADU. That line item is fixed – it’s not a contractor margin.
- Utility connection complexity. Connecting a detached ADU to existing water, sewer, and electrical service is rarely a straight run in Redwood City’s older neighborhoods near Jefferson Avenue or Woodside Road. If the existing utility laterals are undersized or run under a driveway or hardscape, trenching and reconnection costs climb. PG&E service upgrades for larger ADUs add another $2,000-$6,000.
- Finish level and fixture selections. The difference between builder-grade finishes and mid-range selections is roughly $15,000-$30,000 on a full ADU. KraftMaid or Wellborn cabinetry costs more than stock box-store cabinets but holds up better in a rental unit where wear is constant. Cambria or Caesarstone countertops are thicker, harder, and easier to reseal than entry-level quartz. We name the brands in the written quote so you know exactly what you’re getting.
- Title 24 energy compliance requirements. California’s Title 24 energy code is among the most demanding in the country, and new ADU construction in Redwood City must meet it fully. In practice this means higher-performance insulation, dual-pane windows, and often a heat-pump water heater instead of a traditional gas unit. Budget $3,000-$7,000 for the compliance package – it’s not optional, and it affects both design and material selection from the start.
Before
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There are legitimate ways to reduce ADU construction costs in Redwood City without cutting corners that come back as problems at the final inspection or three years into a tenancy. Here’s what actually moves the number.
Start with the right ADU type for your lot
A garage conversion ADU at $30,000-$80,000 is the most cost-effective path if your garage is structurally sound and your lot setbacks allow it under Redwood City’s zoning. A JADU carved from interior space is even less expensive. The savings are real because you’re not paying for foundation, framing, and a new roof from scratch. If a detached ADU is the right answer for your goals – rental income, multigenerational living, resale value – then a detached unit is worth the cost. But don’t build detached when conversion is an option, unless you have a specific reason.
Get the design right before you pull permits
Every design revision after plan check submission costs money – either in re-check fees or in field changes that require a signed change order. At Rowan, we work through design decisions before the drawings go to the city, which is why our projects don’t accumulate the change-order pile that inflates ADU costs at other contractors. The written scope is complete before any permit application goes in.
Avoid premium finish selections in rental units
If the ADU will be a long-term rental, specify durable mid-range finishes rather than high-end ones. KraftMaid cabinets hold up to rental wear; custom millwork doesn’t earn proportionally higher rent. Kohler fixtures at the standard product tier are reliable without the price premium of the designer line. Save the premium selections for a primary residence or a unit you’re building for family.
Consolidate trades under one contractor
Coordinating a general contractor, a separate electrical contractor, a plumber, and a tile installer independently on an ADU project in Redwood City is a project management job that most homeowners aren’t positioned to do while also working full time. Coordination gaps between trades are one of the most common sources of schedule delays and field change costs. Rowan’s seven-trade model means the framing crew, the plumber, the electrician, and the finish carpenter are all working under one written scope and one point of contact.
Get a second opinion on any existing estimate
If you already have a written estimate from another contractor, bring it to us. Rowan offers a free second opinion on any written estimate – we’ll go through it line by line and tell you whether the scope is complete, whether the numbers are in line with the Redwood City market, and whether there are gaps that would likely turn into change orders later. Call (650) 560-7228 to schedule that review at no cost.
Plan for permit timing in your project schedule
This isn’t a cost-reduction tip so much as a cost-protection tip: Redwood City’s Building Division plan check for an ADU currently runs 8-12 weeks for a first submittal. If you’re working with a lender or need the unit ready by a specific date, plan backward from permit issuance, not from when you’d like construction to start. Rushing after a delayed permit often means premium scheduling costs to compress the build timeline.
FAQs – ADU Construction Cost in Redwood City
How much does it cost to build an ADU in Redwood City, CA in 2026?
ADU construction in Redwood City costs $90,000-$220,000 for a fully permitted unit, with most detached ADUs in the 600-850 square foot range landing between $130,000 and $175,000. Garage conversions cost less – typically $30,000-$80,000 – because the shell is already built. The wide range reflects lot conditions, ADU type, permit fees, and finish selections. Call (650) 560-7228 for a written price specific to your property – the estimate is free.
What do Redwood City ADU permit fees cost?
Permit and plan-check fees for an ADU in Redwood City typically run $8,000-$22,000, depending on unit size and type. That figure includes building permit fees, plan check fees, and school impact fees assessed by the Redwood City Unified School District. It does not include engineering fees, which are a separate line item in the design phase. These fees are set by the city and county – they are not a contractor margin, and no reputable contractor can reduce them.
How long does it take to build an ADU in Redwood City?
From signed contract to final inspection, most ADU projects in Redwood City take 9-14 months. Design and engineering typically takes 6-10 weeks. Plan check runs 8-12 weeks for a first submittal, with resubmittals adding 4-6 weeks. Construction itself, once permits are issued, runs 4-6 months for a detached ADU and 2-4 months for a conversion. Lot access constraints in hillside neighborhoods like Emerald Hills can add time at the construction phase. The clearest way to protect your timeline is to get design complete and permit-ready drawings submitted as early as possible.
Is a garage conversion or a detached ADU a better investment in Redwood City?
A garage conversion costs $30,000-$80,000 and gets you to rental income faster, but the unit will be smaller and won’t add the same square footage to your home’s assessed value as a new structure. A detached ADU at $90,000-$220,000 adds a permanent structure with its own address, which typically generates higher rental income and more resale value – Redwood City’s rental market for a one-bedroom ADU currently runs $2,200-$2,800 per month in neighborhoods like Redwood Shores and near the Caltrain corridor. The right answer depends on your lot, your goals, and your budget. Rowan can walk through both options with you and put a written price on each before you decide.
Can I build an ADU myself to save money in Redwood City?
Owner-builder permits are technically available in California, but ADU construction in Redwood City involves multiple inspections across structural, electrical, plumbing, and energy-compliance disciplines – all of which must pass the Redwood City Building Division’s review. Most homeowners who attempt to self-manage ADU construction end up hiring contractors for most of the trades anyway, while absorbing the coordination and permit-management burden themselves. The documented cost of rework, failed inspections, and schedule delays on self-managed ADU projects in San Mateo County typically erodes most of the expected savings. If cost is the concern, a garage conversion with a qualified contractor is a more reliable path to a lower total number than an owner-builder detached ADU.
Does Rowan Construction Group offer a warranty on ADU construction?
Yes. Every ADU Rowan builds in Redwood City is covered by the 365-Day Done Right Promise: if it’s not done right, Rowan makes it right. The warranty is printed on every project page and backed by written terms – not an asterisk. The written scope and written warranty are delivered before work starts, not after. Beyond that, California law requires a 10-year structural warranty on new construction, which applies to all detached ADUs regardless of contractor. Both are in writing before the first crew arrives.
Why Rowan Construction Group for ADU Construction in Redwood City
Grant Rowan founded Rowan Construction Group in 2007 with one administrative discipline that still defines every project: a written price before anyone starts, and no change proceeds without a signed change order. Across 4,000-plus projects, that discipline has kept final costs within a few percent of the agreed number – not because surprises don’t happen on construction sites, but because the process for handling them is documented from the start.
For ADU projects in Redwood City specifically, that matters more than on most jobs. ADU construction involves more permit coordination, more trade sequencing, and more contact with city inspectors than a kitchen remodel or a roof replacement. The documentation that Grant built into the Haven Standard – signed change orders, a photo record on every visit, a written scope before any permit application goes in – is the structure that keeps an 11-month ADU project from drifting.
Our sourcing runs across 50-plus vetted material brands. Framing lumber from established regional suppliers. GAF and Owens Corning roofing on the ADU structure. Kohler or Toto fixtures in the bathroom. KraftMaid or Wellborn cabinetry in the kitchen. Cambria or Caesarstone countertops if you want stone. Every brand named in the written quote is the brand that shows up on the truck – no substitutions without a signed change order.
Background-checked, uniformed crews. A live person answers calls 24/7. A documented photo record on every site visit, included as standard. If you already have a written estimate from another contractor, the Free Second Opinion offer stands: call (650) 560-7228 and we’ll go through it line by line at no charge.
For a full overview of how we approach ADU projects in this market, see our ADU Construction in Redwood City service page, or visit the home page to see the full range of trades we cover.
Key Takeaways
- ADU construction in Redwood City costs $90,000-$220,000 for a detached unit; garage conversions run $30,000-$80,000.
- Most 600-850 sq ft detached ADUs in Redwood City come in at $130,000-$175,000 fully permitted and finished.
- Permit and impact fees alone run $8,000-$22,000 – budget this as a fixed cost, not a contractor line item.
- Plan check at Redwood City’s Building Division runs 8-12 weeks; total project timeline is typically 9-14 months.
- Sloped lots in Emerald Hills, Farm Hill, and Edgewood add $8,000-$25,000 in foundation and site-prep costs versus flat interior lots.
- Title 24 energy compliance adds $3,000-$7,000 but is mandatory on all new ADU construction in California.
- Every Rowan ADU project comes with a flat written price, a written scope, and the 365-Day Done Right Promise – before work starts.
- Free second opinion on any written estimate: call (650) 560-7228.
Get a Written ADU Price for Your Redwood City Property
If you’re planning an ADU in Redwood City and want a number you can actually work with – not a range pulled from a website – call (650) 560-7228. Rowan Construction Group will put a flat written price and a full written scope in your hands before any work starts, on any ADU type, on any lot. Under Clause 1 of the Haven Standard, that’s not a process step. It’s the whole point. Grant Rowan and the team are reachable at that number seven days a week, with a live person answering every call.
Pricing reflects the Redwood City market as of 2026. Rowan Construction Group Redwood City offers free estimates – call (650) 560-7228.
Written by Grant Rowan, Owner at Rowan Construction Group, serving Redwood City since 2007.
What Our Customers Say
"Fence and retaining wall along a sloped boundary. They photographed the footing depth at each post, which mattered when the county inspector came."
- Iona F."Talked us out of the larger scope we came in asking for, because it would not have added the value we thought."
- Emil R."Final invoice was within two percent of the contract. Every change was priced and signed before anyone picked up a tool."
- Malcolm T.