A free site visit, a check of what your lot allows and a written, line-item price.
Get your free estimateTrusted Room Addition Contractor for San Jose Homeowners
Adding a room to your San Jose home means navigating permits, setbacks, foundation work, and a contractor market where the final bill too often looks nothing like the first number you were quoted. Fielding ADU San Jose fixes that with a written price before any work starts and a one-year written guarantee on the finished room from our Room Addition Contractor in San Jose. Reed Calloway leads the Fielding team, and every crew member who steps onto your property is background-checked and uniformed. If you want a room addition priced honestly and built to code, call (669) 201-3984 for a free estimate.
We are an independently owned member of the Garrison Partners family, which has been building to The Garrison Standard since 2006. That means the price goes in writing, permits get pulled, the site gets left clean, and the work is backed in writing for a full 365 days. If something fails in that year, we come back and make it right at no charge.
Sunroom Builders
Sunroom Builders handle glass-walled living spaces that connect your home to the yard with natural light and usable square footage, and in San Jose’s mild climate they get used nearly year-round. Fielding ADU San Jose builds sunrooms as both prefab panel systems and conventional stick-framed structures, depending on the look you want and what your lot will bear. A prefabricated sunroom kit in San Jose typically runs $35,000 to $70,000 installed, while a custom-built sunroom with a slab foundation generally lands between $60,000 and $120,000, with the final price driven by glass package, roof tie-in complexity, and any electrical or HVAC work.
Kit vs. Custom Build
Prefab sunroom kits from Tuff Shed and similar manufacturers go up faster and cost less, but they are limited in size and finish options. A custom sunroom lets us match rooflines, siding, and window styles to your existing house, which matters in older San Jose neighborhoods where the homes have distinct character. We show you both approaches with a written price for each before you choose.
Permitting and Thermal Requirements
San Jose classifies sunrooms as habitable space when they are heated or connected to the home’s HVAC, which triggers Title 24 energy code requirements. An unheated sunroom has a lighter permit path but cannot legally be counted as living area. We pull permits on every sunroom we build, so the square footage is legal if you ever sell.
Room Additions
Room Additions extend your home’s footprint with a new foundation, framed walls, roof tie-in, and finished interior space, and they are the right call when you need a real bedroom, office, or family room rather than a temporary fix. Fielding ADU San Jose builds ground-up room additions in San Jose every month, and our written price covers demolition, foundation, framing, roof, electrical, drywall, paint, and trim per our Room Addition Contractor Maintenance Checklist for San Jose Homeowners. A single-room addition of 200 to 400 square feet in San Jose typically costs $85,000 to $170,000, with the range set by foundation conditions, roof complexity, and finish level, before permit fees.
Foundation and Setback Work
Most San Jose room additions need a new perimeter foundation tied to the existing slab or crawlspace, and almost all of them need a setback variance (the city’s written permission to build closer to the property line than the standard rule allows). We handle the survey, the variance application, and the engineering drawings as part of the job. The written price you approve on day one includes all of it.
Roof Tie-Ins That Do Not Leak
The most common failure point on a room addition is where the new roof meets the old one. We strip the existing roofing back far enough to weave membrane into the new deck, then flash every transition with metal before shingles or tile go back on. The finished tie-in is covered by The Garrison Standard for a full year, and if it leaks in that year, we return and correct it at no charge.
Modular Home Addition
A Modular Home Addition is built in a climate-controlled factory as a complete room module, shipped to your San Jose lot on a truck, and set onto a prepared foundation, then finished on site with plumbing, electrical, and trim connections. Fielding ADU San Jose works with Plant Prefab, Dvele, and Boxabl units, and we manage the site prep, crane coordination, and finish work that those factories do not cover. Modular additions in San Jose typically run $150,000 to $280,000 all-in for a 300 to 500-square-foot module, with factory pricing, transport, crane time, and on-site finish work all in the written number.
Factory Quality and Timeline
Because modular rooms are framed and finished indoors, they avoid the weather delays and material damage that slow down stick-built additions in San Jose’s winter rainy season. A modular addition can go from foundation to occupancy in eight to twelve weeks once permits clear, compared to fourteen to twenty for conventional framing. We show you the factory lead times for the platforms we work with before you commit.
What the Factory Does Not Cover
Modular vendors deliver a box; they do not pull San Jose permits, pour the foundation, set the module, or connect the utilities. That is our job. If you buy a module directly, you still need a licensed contractor on site, and our written price covers everything from uncrating to final inspection.
Home Addition Plans
Home Addition Plans are the architectural drawings, structural engineering, and permit documents that San Jose requires before any room addition can break ground, and they determine what gets built and what it costs. Fielding ADU San Jose produces or coordinates full plan sets for every room addition we price, including floor plans, elevations, structural details, Title 24 energy calculations, and the permit package the city reviews. Plan costs in San Jose for a room addition typically run $4,000 to $12,000 depending on size and engineering complexity, and that cost is included in the written price when you build with us.
Plan Sets That Pass First Review
San Jose’s building department rejects incomplete plan sets routinely, and every resubmission costs you time and money. We submit drawings that address setback, height, lot coverage, and energy code on the first pass because we have built in San Jose long enough to know what the plan checkers look for. Reed Calloway reviews the plans before submittal so nothing obvious gets missed.
Using Your Own Architect
If you already have drawings, we will build from them, and we will flag anything that will not pass San Jose review before you pay permit fees. If you do not have drawings, we can recommend drafters and engineers we work with regularly. Either way, the written price includes plan coordination, not just construction.
In Law Suite Builders
In Law Suite Builders construct attached or detached secondary living quarters with a bedroom, bath, and kitchenette, and they are the practical answer for San Jose homeowners housing aging parents or adult children. Fielding ADU San Jose builds in-law suites as garage conversions, attached additions, and standalone backyard units in San Jose and nearby areas, with the written price covering plumbing, electrical, egress, and finish work. We also serve as a Room Addition Contractor in Santa Clara for similar projects. An attached in-law suite in San Jose typically costs $110,000 to $200,000, while a detached unit runs $160,000 to $300,000 depending on size and utility connections, before permit fees.
Kitchenette vs. Full Kitchen
San Jose treats a kitchenette with a sink and microwave differently than a full kitchen with a range and hood, and the difference affects both cost and permit classification. A kitchenette keeps the project simpler and cheaper; a full kitchen requires ventilation, gas or 240V service, and more plan review. We price both options in writing so you can decide with real numbers.
Separate Entrance Requirements
An in-law suite needs its own exterior door and a safe egress path for the occupant, which changes how we lay out an attached build. For detached units, the walkway, lighting, and door swing all get reviewed by the city. We design the entrance requirements into the plan from day one so they do not become change orders later.
ADU Conversion
An ADU Conversion turns existing square footage like a garage, basement, or utility room into a permitted accessory dwelling unit with its own entrance, kitchen, bath, and sleeping area, and it is the fastest path to a legal rental unit in San Jose. Fielding ADU San Jose converts attached and detached garages in neighborhoods from Alum Rock to Willow Glen, and we handle the structural retrofit, insulation, utility upgrades, and city inspection. A garage conversion to an ADU in San Jose typically runs $90,000 to $160,000 for a one-bedroom unit, with the range driven by foundation condition, electrical panel capacity, and whether you need a new sewer line.
Garage Conversion Specifics
Garage conversions require raising the floor above the garage slab, adding insulation to meet Title 24, and often replacing the panel to carry the new kitchen and bath loads. If the garage roof is tied to the house, we also need engineering for the new ceiling and any beam work. Our site visit identifies these costs up front so they are in the written price, not added later.
Detached ADU Conversions
A detached garage that gets converted into an ADU has more flexibility on placement and noise separation but usually needs a new sewer lateral and separate gas and electric meters or subpanels. San Jose encourages detached conversions through reduced parking requirements in many zones. We confirm the property’s specific zoning allowances before you spend a dollar on plans.
Brands We Service
We work with Plant Prefab on modular room additions and ADUs, and we know their panelized wall systems well enough to handle site prep, crane setting, and finish work without surprises. Their modules arrive with factory-built wall panels and we handle the foundation, utility connections, and interior finish, plus any San Jose-specific plan review their standard details do not cover.
We install Tuff Shed structures for homeowners who want a prefab sunroom or studio shell at a lower price point, and we handle the foundation, assembly, and any electrical or finish work the base kit does not include. James Hardie siding is our standard exterior finish on conventional builds when we want durable, fire-resistant cladding that holds paint better than wood. Whether you have a Plant Prefab module, a Tuff Shed kit, or a James Hardie-clad addition, we can help you get it permitted and finished in San Jose and surrounding communities. We also work as a Room Addition Contractor - Sunnyvale homeowners can rely on for the same quality builds.
Signs You Need a Pro Right Now
- You have a room addition drawing but no permit path. A plan that has not been through San Jose plan check is just paper. If a previous contractor handed you drawings and disappeared, you need a builder who submits and pulls the permit before work starts.
- You got a room addition quote that doubled after demo started. Contractors who price low to get the job then hit you with change orders are common in San Jose. A written price that survives the whole project is not optional; it is the only way to know what you are actually spending.
- Your home has foundation movement or drainage problems near the planned addition. Adding square footage to a house with settlement issues makes the problem worse. We inspect the existing foundation and site drainage as part of the estimate so the new room does not inherit old problems.
- Your electrical panel is full and the addition needs a kitchen or bath. A room addition with a new circuit load often requires a panel upgrade, and San Jose will not pass final inspection without one. We check amp capacity and service wire size during the site visit.
- You need the work permitted but the last contractor would not pull one. Unpermitted additions become a problem at resale and a liability if something fails. We build by the book on every job, and the permit card stays posted until final inspection passes.
Our Process, Step by Step
- 1
Site visit and measurements. We walk the property, measure the existing structure, check the foundation, panel, and sewer, and talk through what you want the room to do. This visit is free and takes about an hour.
- 2
Written price and scope. We put the full project scope and price in writing before any work starts, including permit fees, materials, labor, and the plan set. The number you approve on day one is the number on the final invoice.
- 3
Plans, engineering, and permit submittal. We coordinate drawings, structural calculations, Title 24 energy compliance, and the San Jose permit package. Plans are reviewed for completeness before submittal so the city does not bounce them back.
- 4
Construction and weekly updates. The crew arrives in uniform, background-checked, and the same team runs the job from framing through finish. You get a straight answer on progress each week, and permits stay posted.
- 5
Final inspection and the written guarantee. We walk the finished room with you, pass city final inspection, and hand you The Garrison Standard guarantee in writing: workmanship defects are covered for 365 days, and if something fails, we return and correct it at no charge.
How Much Does Room Addition Contractor Cost in San Jose?
A typical room addition in San Jose runs $85,000 to $170,000 for a 200 to 400-square-foot ground-up build, while a garage conversion runs $90,000 to $160,000, a sunroom $35,000 to $120,000 depending on kit or custom, and a modular addition $150,000 to $280,000. Permit fees in San Jose add $3,000 to $8,000 depending on project size and school district fees, and we include those in the written price so there are no surprises at plan check.
What moves the price is foundation condition, roof tie-in complexity, whether you need a panel upgrade or sewer line replacement, and the finish level you choose. The way to avoid overpaying is to get a written scope that includes everything from demo to final paint, so a low bid that omits the panel upgrade or the variance application cannot turn into a change order. Our free estimate includes a line-item written price covering the full scope, and you can call (669) 201-3984 to schedule one.
Our Service Area Near San Jose
Fielding ADU San Jose builds room additions across San Jose proper, including Alum Rock, Willow Glen, Cambrian, and Evergreen neighborhoods. We also serve Sunnyvale, Campbell, Santa Clara, Saratoga, and Menlo Park. Most estimates are scheduled within a few days, and we are honest about when we can start: we would rather tell you a real start date than make one up to win the job. Get more background on how we work on our home page.
Serving San Jose, CA - Our Local Coverage Area
We’re based in the San Jose area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
Frequently Asked Questions About Room Addition Contractor in San Jose
A room addition contractor is a licensed builder who extends your home’s footprint with new foundation, framing, roof, and finished interior space, and who pulls the permits and passes the inspections San Jose requires. Fielding ADU San Jose is an independently owned Garrison Partners location led by Reed Calloway, and we price every room addition in writing before work starts. Call (669) 201-3984 to schedule a free estimate.
A conventional ground-up room addition in San Jose typically takes fourteen to twenty weeks from permit approval to final inspection, and plan review adds four to eight weeks on top of that. Modular additions move faster, often eight to twelve weeks after permits clear. We give you a written schedule with the written price before you commit.
Most San Jose room additions cost between $85,000 and $170,000 for a single room of 200 to 400 square feet, before permit fees. The price is driven by foundation work, roof complexity, finish level, and any utility upgrades. Call (669) 201-3984 for an exact quote, and the estimate is free.
Yes, we work with Plant Prefab modular units and Tuff Shed prefab structures, handling site prep, foundation, utility connections, and finish work. We also build conventional additions with James Hardie siding. The written price covers the full build, not just the parts we like.
Room additions are planned construction, not emergency response, so we do not promise same-day starts on a build. What we do promise is that a live person answers the phone 24 hours a day, 7 days a week, so you can reach us at noon or midnight to ask questions or schedule an estimate. Call (669) 201-3984 and a person picks up.
The Garrison Standard covers workmanship defects for 365 days from project completion, and it is spelled out on paper: what it covers, how long it runs, and exactly how we make it right if something fails. If the work fails inside that year, we return at no charge and correct the defect. You get this guarantee in writing on every room addition we build.
Have your property address, a rough idea of the square footage you want, and any HOA rules or lot survey documents handy. We will walk the site, check the foundation, panel, and sewer, and give you a written price that covers the full scope. The estimate is free and you are not obligated to build.
Schedule Your Room Addition Contractor Service in San Jose Today
Get a written price before any work starts, from a crew that pulls permits and stands behind the build for a full year. Call (669) 201-3984 for a free, no-obligation estimate on your San Jose room addition, sunroom, in-law suite, or ADU conversion. A live person answers, twenty-four hours a day, seven days a week.
Written by Reed Calloway, Owner at Fielding ADU San Jose, serving San Jose since 2006.
