Home Additions & ADU in San Jose - One Fixed Price, Permits Handled

Fast, Reliable Home Additions & ADU Across San Jose

Home additions and ADU construction in San Jose typically run $53,100-$153,400 for room additions and $106,200-$259,600 for detached ADUs, with most projects moving through permitting in 4-8 months depending on whether you use the city’s pre-approved plan program. We also offer Bathroom Remodeling in San Jose. We build across San Jose, from the post-WWII ranch tracts in Berryessa and Alum Rock to the Craftsman stock in Willow Glen and the hillside lots in Evergreen and Almaden. Our crews are dispatched from the San Francisco Bay Area office, and we carry the same written-price discipline to every San Jose job we quote. Call (669) 202-9618 to schedule your free estimate.

Call (669) 202-9618

Why Rowan Construction Group Cupertino Is San Jose’s Preferred Home Additions & ADU Company

We’ve delivered 4,000-plus projects since 2007, every one with a written price before work started and a documented photo record when the crew left. In San Jose, that discipline matters more than in most markets because the work here is rarely just the work you see on the surface.

Our Home Additions & ADU team knows the difference between a Berryessa ranch on a raised wood-frame foundation and a Willow Glen Craftsman on post-and-pier. We’ve walked the permit path through San Jose’s Building Division enough times to know when the pre-approved ADU plan program saves six weeks, and when a custom design is worth the extra plan-check cycle. Customers in San Jose leave us three-star reviews that mention specifics - the photo record, the signed change order, the flat price that held - and that’s the audience we build for.

Calls are answered by a live person 24/7. Crews are background-checked and uniformed. And under Clause 1 of The Haven Standard, the price is written before anyone picks up a tool.

Our Home Additions & ADU Services in San Jose

ADU Design & Permitting

San Jose’s pre-approved ADU plan program is one of the most aggressive in California, and we use it when the site fits. A pre-approved plan can cut plan-check time from 12-16 weeks to 4-6 weeks, which on a $1M+ lot in Cambrian or West San Jose translates to real carrying-cost savings. We also run custom designs when the lot geometry, setback, or WUI code in the Evergreen or Almaden foothills demands it. Every permit package we submit includes the seismic scope the Building Division will flag - cripple-wall bracing, post-and-pier upgrades, shear-wall details - so the first plan-check round isn’t a surprise.

Garage Conversion ADU

Garage conversions in San Jose run $35,400-$94,400 and make sense on the narrow lots of Willow Glen or the Rose Garden where there’s no room to build detached. The catch is the existing house. In Berryessa and Alum Rock, that 1950s ranch with the tuck-under garage almost certainly has an unreinforced cripple wall and a raised foundation that the city will require you to address before the ADU certificate of occupancy issues. We price that scope upfront, not as a change order six months in.

New Detached ADU

A new detached ADU in San Jose is the most expensive residential construction most homeowners undertake, and the most regulated. The WUI code applies in Evergreen, Silver Creek, and the Almaden foothills - Class A roofing, ember-resistant venting, ignition-resistant siding - and the expansive Adobe clay in Almaden and Blossom Hill demands pier underpinning or engineered fill rather than standard slab-on-grade. We specify hot-dip or stainless fasteners and hardware on every exterior connection, because marine fog and salt air push up the valley farther than most inland contractors account for. The $106,200-$259,600 range covers slab to finish; the variation is site work and foundation, not finishes.

Junior ADU & Interior Conversion

Junior ADUs - conversions within the existing footprint, with a separate entrance - work on the smaller lots of central San Jose where setbacks kill a detached build. The 1920s-1940s stock in Willow Glen and the Rose Garden often has knob-and-tube-era framing and post-and-pier foundations that have to be brought to current code. We open walls with the expectation of finding something, document it with photos, and write the change order before the next phase starts. No work proceeds on a change until the change order is signed. That’s the discipline Haven acquired Rowan for.

Before

After

Trusted Brands We Service in San Jose

We source across fifty-plus vetted brands, and we stock the hardware that holds up in San Jose’s conditions. For fencing and exterior railings on ADU projects, we specify Master Halco and Ameristar components with hot-dip galvanized or powder-coated finishes - electro-galvanized posts chalk out in the marine-influenced air within five to seven years. For windows and doors in WUI zones, we use ViewLux products with tempered, ember-resistant screening. Barrette railing systems go on decks and exterior stairs where code requires graspable handrails. We don’t inflate the quote with brand names you don’t need, and we don’t spec hardware that fails early to hit a lower number.

Common Home Additions & ADU Problems We See in San Jose Homes

• Coastal-spec fasteners failing inland. Marine fog and salt air push south through the valley more than most contractors admit. Electro-galvanized fence posts and standard zinc roof fasteners on an Evergreen or Silver Creek addition chalk and corrode within a decade. We specify hot-dip galvanized or stainless hardware on every exterior connection, and we price it in from the start.
• Expansive clay ignored in site prep. The Adobe clay from Almaden through Blossom Hill swells in winter and shrinks in summer. Crews that pour flatwork or set pavers without a proper compacted base and drainage layer see slab heave and joint separation by the first wet season. We engineer the base for the soil, not for the schedule.
• Permit paths that skip seismic. San Jose’s mandatory soft-story retrofit ordinance and the ADU program run through the same Building Division. An ADU on a Berryessa or Alum Rock lot almost always pulls the existing house into a seismic scope - cripple-wall bracing, post-and-pier upgrades - that a Fresno or Sacramento builder would never price in. We do.
• WUI code blind spots. The wildland-urban interface in Evergreen, Almaden, and Silver Creek requires Class A roofing, ember-resistant venting, and ignition-resistant siding. Contractors who miss it in the permit submittal get months of plan-check corrections and change orders. We flag it in the first site visit.

Pricing for Home Additions & ADU in San Jose, CA

We Also Serve Cities Near San Jose

Our crews build across the South Bay, including Home Additions & ADU in San Jose and the surrounding cities of Milpitas, Santa Clara, Sunnyvale, and Campbell. Each city has its own permit pathway and soil conditions; we quote them accurately rather than templating San Jose numbers across the map.

FAQs - Home Additions & ADU in San Jose