Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
Before
After
Before
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Before
AfterTrusted Home Additions & ADU for Redwood City Homeowners
Home additions and ADU construction in Redwood City typically run $45,000-$130,000 for room additions and $90,000-$220,000 for detached ADUs, with most projects taking 4-12 months from permit to final inspection. Rowan Construction Group has delivered 4,000-plus projects since 2007 through our Home Additions & ADU in Redwood City, every one with a written price before work started and a documented photo record when the crew left. We’re led by Grant Rowan and operate under The Haven Standard, which means no change proceeds without a signed change order and your project finishes within a few percent of the number you agreed to. Call (650) 560-7228 to schedule your free estimate.
What Our Home Additions & ADU Service Includes
ADU Design & Permitting
An accessory dwelling unit, or ADU, is a self-contained living space on the same lot as a primary residence - either attached, converted from existing space, or built new and detached. In Redwood City, the permitting path runs through San Mateo County’s unincorporated guidelines or the city’s municipal code, depending on your parcel’s jurisdiction, and the difference affects setbacks, parking requirements, and utility tie-in rules. We prepare architectural plans, structural calculations, and energy compliance documentation (Title 24) as part of our flat written quote, so you’re not hiring separate designers and hoping the numbers reconcile later.
Garage Conversion ADU
Converting an existing garage into living space is often the fastest path to rental income or multigenerational housing in Redwood City, where lot sizes in neighborhoods like Mount Carmel and Farm Hills can limit new footprint options. The existing slab, framing, and roof structure must be evaluated for habitability - we check ceiling height, ventilation, and whether the foundation meets current seismic standards. Our crews handle the full conversion: insulating and finishing walls, adding a kitchenette and bath, upgrading electrical to 200-amp service if needed, and running plumbing from the main line, all documented with photos at each phase.
New Detached ADU
A detached ADU is a standalone structure, typically 400-1,200 square feet, built from foundation to finish on your Redwood City property. These projects require full site prep, including grading for drainage compliance, trenching for sewer and water connections, and often upgrading the main electrical panel to handle the additional load. We source framing lumber, windows, and roofing through our fifty-plus vetted brand relationships - including ECO Window Systems for energy-efficient units that meet California’s stringent Title 24 requirements - so your written quote reflects actual material costs, not inflated placeholders.
Junior ADU & Interior Conversion
A Junior ADU, or JADU, is created within the walls of an existing single-family home, limited to 500 square feet and requiring a separate entrance but sharing bathroom or kitchen facilities with the main dwelling. In Redwood City’s older stock - the bungalows near downtown and the Eichler-influenced homes in the Avenues - this often means reconfiguring a ground-floor bedroom suite or converting a portion of the basement. We assess load-bearing walls, egress window requirements, and whether your HVAC system can handle zoned climate control before quoting, so the price you sign reflects real conditions, not assumptions.
ADU Site Prep & Utilities
Site preparation for any ADU in Redwood City involves more than clearing space - it’s about understanding the specific geology of the San Francisco Peninsula, where clay-heavy soils in the flats and rocky substrate in the Woodside Road corridor demand different foundation strategies. We handle grading, utility trenching, sewer lateral upgrades, and electrical service expansion, coordinating with PG&E and the Redwood City Public Works Department to keep permits on track. Every site visit includes a documented photo record of soil conditions, utility locations, and drainage patterns, so you have evidence of what we found and why we recommended the approach we did.
Room Additions
A room addition extends your existing home’s footprint - a master suite, family room, or home office - and must tie into the existing structure without compromising roof lines, foundation integrity, or seismic performance, as we also ensure with Home Additions & ADU - Palo Alto. In Redwood City’s hillside zones, like Emerald Hills and Farm Hills, we regularly see projects where the addition requires engineered retaining walls or pier foundations to address slope stability. We match siding, roofing, and window styles to the existing home using brands like CWS and ES Windows, and every quote includes a written scope specifying how we integrate the new structure with the old.
Second Story Additions
Adding a second story is the most complex residential addition, requiring evaluation of the existing foundation’s capacity to carry doubled live and dead loads. Redwood City’s mix of 1950s ranch homes and newer construction means we encounter everything under-engineered post-and-beam supports to modern slab-on-grade that needs reinforcement. We bring in a structural engineer as part of our standard process, not as a surprise add-on, and the written quote specifies whether your foundation needs sistering, underpinning, or a complete rebuild - no change order appears without your signature.
Sunrooms & Enclosed Patios
Sunrooms and enclosed patios occupy a middle ground between outdoor living and conditioned space, and in Redwood City’s mild climate, they’re usable year-round with proper glazing and insulation. We distinguish between three-season rooms (unconditioned, with single-pane windows) and four-season sunrooms (HVAC-connected, with dual-pane low-E glass and insulated slabs). The choice affects your permit path, your property tax assessment, and your utility costs - we explain the tradeoffs in writing before you decide, because Clause 1 of The Haven Standard requires the price to be set before anyone starts.
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.
Brands We Service for Home Additions & ADU
We’ve installed CWS window and door systems across hundreds of Redwood City projects, from full-home additions to ADU conversions in the Mount Carmel neighborhood. CWS vinyl and aluminum frames meet California’s Title 24 energy standards without the premium pricing of some competitors, and we stock common sizes and hardware to avoid the delays that plague special-order jobs. Our crews are trained on CWS installation specifics - including the weep screed details that prevent moisture intrusion in our coastal climate, where fog-driven condensation is a real concern eight months of the year.
ES Windows is our go-to for projects requiring impact-rated or high-performance glazing, particularly second-story additions and hillside homes in Emerald Hills where wind exposure matters. We’ve sourced ES Windows for both new construction and retrofits, and our written quotes specify the exact performance ratings - U-factor, SHGC, and design pressure - rather than generic “energy efficient” language. Whether you have CWS, ES Windows, ECO Window Systems, CGI, or any other make specified by your architect or preferred for budget reasons, we can source, install, and warranty the work under our 365-Day Done Right Promise.
Before
AfterSigns You Need Home Additions & ADU Right Now
- Your household has outgrown the existing floor plan. Three-bedroom homes built in the 1960s and 1970s throughout Redwood City’s Redwood Shores and Edgewood neighborhoods were designed for families of three or four. When adult children return, aging parents move in, or remote work becomes permanent, the walls don’t move - but we can add new ones, with a written price before demolition starts.
- You’re paying Bay Area rent for a family member elsewhere. At $3,000-$4,500 monthly for a one-bedroom in San Mateo County, eighteen months of rental payments covers a significant portion of a garage conversion ADU. The math works faster than most homeowners calculate, and we run the numbers with you during the free estimate - no obligation, no follow-up pressure.
- Your garage or basement sits unfinished while your home lacks functional space. Unfinished square footage in Redwood City is a missed opportunity in a market where every habitable square foot adds measurable value. We assess whether your existing structure can be converted under current code or whether a new detached unit makes more financial sense, and we put both paths in writing with line-item pricing.
- Your property’s zoning changed under California’s ADU laws. SB 9 and subsequent legislation have preempted many local restrictions, but Redwood City’s specific implementation - including owner-occupancy requirements and front setback rules - still affects what you can build and where. We track these changes and flag opportunities (or constraints) during our initial site evaluation, so your permit application isn’t rejected for a rule you didn’t know existed.
- The foundation or roof shows stress from deferred maintenance. Cracks in the slab, sagging rooflines, or water intrusion in the crawl space aren’t just maintenance issues - they’re warnings that your home’s structure may not support an addition without remediation. We document these conditions with photos, explain what they mean for your project timeline and budget, and include any necessary structural work in the original quote rather than discovering it mid-project.
Our Home Additions & ADU Process - Step by Step
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Site evaluation and feasibility study. We visit your Redwood City property, measure existing structures, photograph conditions, and review your parcel’s zoning on San Mateo County’s GIS system. Within 48 hours, you receive a written feasibility summary - not a commitment, but a clear-eyed assessment of what’s possible, what permits will cost, and what obstacles we see.
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Architectural design and engineering. If you proceed, we produce scaled plans, structural calculations, and Title 24 energy compliance documentation. For ADUs, this includes kitchen and bath layouts; for room additions, it specifies how new roofing ties into existing valleys and ridges. Everything is submitted for permit on your behalf, with permit fees listed as a line item in your quote.
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Written quote with fixed scope. Under Clause 1 of The Haven Standard, you receive a flat price with a written scope and a written warranty before any work begins. The quote breaks out materials, labor, permits, and any subcontracted trades (electrical, plumbing, HVAC). No “allowances” that balloon later. No “call for final pricing.” The number is the number.
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Construction with documented progress. Our background-checked, uniformed crews work on a schedule you approve, with a dedicated project manager updating you weekly. Every visit generates a documented photo record - foundation pour, framing inspection, rough electrical, insulation, final walkthrough - delivered to you as standard, not as a paid upgrade. No change proceeds without your signed change order.
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Final inspection and 365-Day Done Right Promise. We pull all permits, schedule inspections, and don’t request final payment until the city signs off. Then our 365-Day Done Right Promise takes effect: if anything we built isn’t right, we make it right - backed by The Haven Standard’s terms page, not a handshake. The warranty, the photo record, and your final invoice are your documentation.
How Much Does Home Additions & ADU Cost in Redwood City?
A typical room addition in Redwood City runs $45,000-$130,000 depending on square footage, foundation requirements, and finish level. ADU construction costs more - $90,000-$220,000 for detached units, $30,000-$80,000 for garage conversions - because full kitchens, bathrooms, and separate utility meters add fixed costs regardless of size. In the Farm Hills and Mount Carmel neighborhoods, where lots are flatter and utility connections shorter, we’ve seen projects land in the lower third of these ranges, similar to what we find with Home Additions & ADU - San Carlos. Hillside properties in Emerald Hills or near Woodside Road often require engineered foundations and longer utility trenches, pushing costs toward the upper end.
Several factors move the needle on your specific quote. Soil conditions determine whether a standard footing works or if you need pier-and-grade-beam construction. Roofing complexity - tying into an existing gable versus building a new hip roof - affects both material and labor hours. Window and door selections from our vetted brands (CWS, ES Windows, ECO Window Systems, CGI) range from functional to premium, and we quote each tier separately so you can compare. Finish specifications - quartz versus laminate countertops, custom tile versus fiberglass shower surrounds - are itemized, not bundled into vague “package” pricing.
To avoid overpaying, get multiple written quotes and bring them to us for a Free Second Opinion - we’ll review competitor estimates line by line at no charge, flagging scope gaps or inflated allowances we’ve seen across 4,000-plus projects. Our quotes include permits, inspections, and the documented photo record as standard; if another quote excludes any of these, the real cost is higher than the paper suggests. Call (650) 560-7228 for your written estimate.
Home Additions & ADU Near Redwood City - Our Service Area
We build home additions and ADUs throughout the San Francisco Peninsula, with regular projects in Home Additions & ADU in San Carlos, Home Additions & ADU in Menlo Park, Belmont, Emerald Lake Hills, San Mateo, Woodside, Palo Alto, Hayward, Mountain View, Los Altos, and Sunnyvale. Most Redwood City homeowners see us for initial site evaluation within two business days of calling, and our project managers live in the communities they serve - so they know which San Mateo County inspector handles ADU electrical in Redwood Shores versus the unincorporated hills. Whether you’re adding a room in Farm Hills or converting a garage in Mount Carmel, the crew that quotes your job is the crew that builds it.
Serving Redwood City, CA - Our Local Coverage Area
We’re based in the Redwood City area and know this community well, and we also offer Menlo Park Home Additions & ADU services. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
Frequently Asked Questions - Home Additions & ADU in Redwood City
A home addition expands your existing dwelling - adding rooms, stories, or enclosed space - while an ADU (accessory dwelling unit) creates a separate, self-contained living unit on the same lot. Choose an addition when you need more space for your own household; choose an ADU when you want rental income, multigenerational housing with privacy, or future flexibility. Call (650) 560-7228 and we’ll assess your property, goals, and zoning to recommend the path with the best return.
Room additions typically take 3-6 months from permit to completion; ADUs run 6-12 months depending on complexity, with detached units and new utility connections taking longest. Permit timelines vary - San Mateo County’s unincorporated areas and Redwood City’s planning department have different backlogs, and we track both so your quote includes realistic scheduling. Call (650) 560-7228 for a timeline estimate based on current permit conditions.
Room additions in Redwood City range $45,000-$130,000, while ADU construction runs $90,000-$220,000 for detached units and $30,000-$80,000 for garage conversions. ADUs cost more per square foot because they require full kitchens, bathrooms, and independent utility connections. Every Rowan quote breaks these elements out separately so you see where your money goes - call (650) 560-7228 for a written price before any work starts.
Yes - we’ve installed CWS, ES Windows, ECO Window Systems, and CGI products across hundreds of Peninsula projects, and our relationships with these manufacturers mean competitive pricing and no special-order delays. If your architect specifies another brand or you have a preference, we source and install it with the same written warranty. Call (650) 560-7228 to discuss material options for your project.
We don’t claim same-day emergency dispatch for planned construction work - home additions and ADUs are scheduled projects, not emergencies. However, if we discover unexpected structural conditions during demolition (compromised foundation, hazardous materials, active leaks), we halt work, document the condition with photos, and present a signed change order with solutions before proceeding. A live person answers our phones 24/7 to coordinate urgent site issues.
Every project is backed by our 365-Day Done Right Promise: if anything we built isn’t right, we make it right - backed by The Haven Standard’s terms page, not an asterisk. This covers workmanship, materials, and integration with existing structures. The warranty is printed on every page of your quote and activated on final inspection approval. Call (650) 560-7228 for warranty terms in writing.
Gather any existing property surveys, architectural plans, or previous inspection reports; note your approximate budget range and intended use (rental, family, office); and identify any absolute constraints (protected trees, easements, neighbor proximity). We’ll handle zoning research, site measurement, and feasibility analysis from there. Call (650) 560-7228 to schedule - estimates are free, written, and delivered with no obligation.
Schedule Your Home Additions & ADU Service in Redwood City Today
Call (650) 560-7228 to schedule your free, written estimate for home additions or ADU construction in Redwood City. You’ll speak with a live person, 24/7, and receive a flat price with a written scope before any work starts - that’s Clause 1 of The Haven Standard, and it’s been our practice since 2007. Bring a competitor’s quote for a Free Second Opinion; we’ll review it line by line at no charge. Grant Rowan and the team at Rowan Construction Group are ready to show you what documented, disciplined construction looks like.
Written by Grant Rowan, Owner at Rowan Construction Group, serving Redwood City since 2007.