Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
Before
After
Before
After
Before
AfterFast, Reliable Home Additions & ADU Across Los Gatos
A home addition in Los Gatos typically runs $45,000-$130,000, while a detached ADU starts around $90,000 and can reach $220,000 depending on foundation type, hillside conditions, and the Town’s independent permitting pipeline. Crews from our Home Additions & ADU in Los Gatos operation are dispatched from the San Francisco Bay Area office and carry the local soils and fire-zone knowledge that keeps hillside projects moving. Call (650) 405-3637 to schedule your free estimate - we’ll bring a written price, not a promise.
Why Rowan Construction Group Sunnyvale Is Los Gatos’s Preferred Home Additions & ADU Company
We’ve delivered more than 4,000 projects since 2007, every one with a written price before work started and a documented photo record when the crew left. Los Gatos homeowners find us through the three-star reviews - the ones that mention exactly what was found behind the walls and how it was handled in writing.
Our crews know the difference between a valley-floor ranch near Los Gatos-Saratoga Road and a hillside custom above Kennedy Road. That local knowledge matters when the Town of Los Gatos building department requires a soils report and Conceptual Development Plan approval that county-permit neighbors skip entirely. We build that timeline into the schedule from day one.
Calls are answered by a live person 24/7. Technicians arrive background-checked and uniformed. And under Clause 1 of The Haven Standard, the price is written before anyone picks up a tool - on every trade, including Home Additions & ADU.
Our Home Additions & ADU Services in Los Gatos
ADU Design & Permitting
ADU construction in Los Gatos sits at $90,000-$220,000, but the real variable is time. The Town’s independent building department moves through soils reports, grading permits, and Conceptual Development Plan review before a building permit is even accepted - a pipeline two to three months longer than Campbell or Sunnyvale. We front-load that permitting work and price it into the contract, so the schedule you see is the schedule you get. Our design team coordinates the geotechnical referral and prepares the CDP submittal as part of the flat written quote.
Garage Conversion ADU
A garage conversion in Los Gatos runs $30,000-$80,000, with the lower end covering valley-floor slabs and the upper end reflecting hillside lots where the garage sits on a slope and needs foundation reinforcement. Many Los Gatos garages, especially in the historic downtown district and older hillside neighborhoods, were built without the seismic anchoring or fire-resistant envelope that Chapter 7A now requires for habitable space. We inspect the slab, the shear connection to the main house, and the existing electrical service before quoting - then write allowances for cloth wiring, panel upgrades, and any rim-joist damage from old deck flashing.
New Detached ADU
Detached ADUs on Los Gatos hillside lots are structurally bespoke. The western neighborhoods transition into Very High Fire Hazard Severity Zones, which means ignition-resistant siding, tempered glazing, and extended defensible-space grading - all Chapter 7A requirements that flatland builders rarely encounter. The foundation is almost never a standard slab. Caissons, grade beams, or drilled piers are specified once the geotechnical report lands, and we price those engineered systems as line items in the written quote, not as surprises after excavation.
Junior ADU & Interior Conversion
Junior ADUs work well in Los Gatos’s larger historic homes and mid-century valley ranches where a separate entrance and kitchenette can be carved from existing square footage. The constraint is usually the electrical service and the sewer lateral, not the floor plan. We verify panel capacity and drainage slope before quoting, and we write allowances for the rewire or plumbing reroute that pre-1990 construction often needs.
Second Story Additions
Second story additions are where Los Gatos’s older housing stock gets interesting. On a 1960s ranch above Kennedy Road in the Los Gatos hills, our crew opened a rear wall for a second-story addition and found undersized 2×4 load-bearing framing, cloth-wrapped wiring with no ground, and a previous deck’s failed waterproofing that had rotted the rim joist and subfloor. We priced a shear-wall upgrade, full rough-in rewire, and new flashing detail as written change orders before touching anything, then passed the Town of Los Gatos inspection sign-off on the first rough-in walk after pulling the independent grading permit the hillside triggered. That discipline - inspect, document, price in writing, then build - is what keeps our projects within a few percent of the agreed cost.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
- 2
You get an upfront price rangeHonest numbers before anyone is dispatched.
- 3
A background-checked tech heads outLicensed & insured, dispatched right away.
- 4
You approve before work beginsNothing starts until you say go.
Before
AfterTrusted Brands We Service in Los Gatos
We source across fifty-plus vetted brands, and for ADU and addition work we regularly specify Dvele’s precision-manufactured panel systems for faster enclosed-shell timelines on hillside lots where weather exposure matters, Mighty Buildings’ 3D-printed units for compact detached ADUs on tight setbacks, and Cover’s design-permit-build package for homeowners who want a single accountable party through the Town of Los Gatos’s extended review pipeline. Every brand is priced at honest trade cost in the written quote - no inflated retail padding to cover unknowns.
Common Home Additions & ADU Problems We See in Los Gatos Homes
- Bidding off flatland assumptions on hillside lots. A Los Gatos hillside addition priced on a standard slab assumption will blow up once the geotech report calls for caissons or drilled piers. We order the soils report before quoting, or we write a foundation allowance with a ceiling and a clear trigger.
- Skipping the Town’s Conceptual Development Plan or independent grading permit. Treating Los Gatos like a county-permit city stalls the project two to three months before a permit is even accepted. We map the full Town pipeline in the project schedule and handle the CDP submittal ourselves.
- Opening pre-1990 walls without allowance language. Cloth wiring, undersized framing, and Loma Prieta-era shear damage are common in Los Gatos’s large inventory of pre-1990 custom homes. We write specific allowances into the contract, then inspect and document before demo. Any surprise is priced and approved in writing before we touch it.
- Ignoring Chapter 7A fire-resistant material requirements. The western and upper Los Gatos neighborhoods sit in CAL FIRE Very High Fire Hazard Severity Zones. Ignition-resistant siding, tempered glazing, and extended defensible space aren’t upgrades here - they’re code. We specify them in the base quote, not as change orders mid-project.
Pricing for Home Additions & ADU in Los Gatos, CA
These are the ranges we write on our quotes for Los Gatos work. Every number is a flat price with a written scope and a written warranty - “call for a quote” is not an option here.
| Service | Price Range in Los Gatos |
|---|---|
| Home Addition | $45,000 - $130,000 |
| ADU Construction | $90,000 - $220,000 |
| Garage Conversion | $30,000 - $80,000 |
What moves the number within these ranges: hillside versus valley-floor foundation type, the extent of seismic or fire-zone code upgrades, the condition of existing electrical and plumbing when walls open, and the length of the Town of Los Gatos permitting pipeline. We handle that last variable by front-loading the CDP and grading permit work, so the construction schedule isn’t held hostage by review cycles.
Bring any competitor’s written estimate and we’ll review it line by line at no charge - our Free Second Opinion. Then we’ll deliver our own flat written price before any work starts. Call (650) 405-3637.
We Also Serve Cities Near Los Gatos
Our crews work across the South Bay, including Saratoga, Campbell, Cupertino, and Santa Clara. Each city has its own permitting authority and its own typical foundation conditions - Saratoga shares Los Gatos’s hillside challenges, while Campbell and Santa Clara run through Santa Clara County’s faster permit pipeline. We calibrate our quotes and schedules to the actual jurisdiction, not a regional average.
Serving Los Gatos, CA - Our Local Coverage Area
We’re based in the Los Gatos area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs - Home Additions & ADU in Los Gatos
The Town of Los Gatos operates its own building department, and hillside projects must clear a soils/geotechnical report, an independent grading permit, and Conceptual Development Plan approval before a building permit is even accepted - a pipeline that runs two to three months longer than county-permit neighbors. That extended review adds professional fees and carrying costs that we itemize in the written quote, not bury in overhead. Call (650) 405-3637 for an exact quote - estimates are free.
Cloth-wrapped wiring with no ground, undersized 2×4 load-bearing framing, and failed waterproofing from old deck or roof details are the most common discoveries in pre-1990 Los Gatos construction, especially in hillside custom homes near the 1989 Loma Prieta epicenter. We write specific allowances for these conditions into every contract, then inspect and document before demo. Any needed upgrade is priced and approved in writing before work proceeds - no surprise change orders mid-project. Call (650) 405-3637 for an exact quote - estimates are free.
Yes, if the property sits in the western or upper Los Gatos neighborhoods that CAL FIRE designates as Very High Fire Hazard Severity Zones. Chapter 7A of the California Building Code requires ignition-resistant siding, tempered glazing, and extended defensible-space grading on new construction and substantial remodels in these zones - requirements that flatland South Bay jurisdictions rarely encounter. We specify Chapter 7A materials in the base quote, not as upgrades. Call (650) 405-3637 for an exact quote - estimates are free.
We inspect first, write allowances into the contract for common hidden conditions, and require a signed change order before any surprise work proceeds. On a recent Kennedy Road second-story addition, we found rotted rim joists, cloth wiring, and undersized framing - all documented, priced in writing, and approved before demo continued. That discipline is why our projects finish within a few percent of the agreed price. Under Clause 1 of The Haven Standard, the price is written before anyone starts. Call (650) 405-3637 for an exact quote - estimates are free.
Yes, but the foundation will be engineered - caissons, grade beams, or drilled piers rather than a standard slab - and the project will need the full Town of Los Gatos hillside permit pipeline including soils report, grading permit, and CDP approval. We order the geotechnical investigation before quoting and price the engineered foundation as a line item. Dvele and Mighty Buildings both manufacture systems that adapt well to engineered pier foundations, and we source them at trade cost. Call (650) 405-3637 for an exact quote - estimates are free.
Ready to add square footage to your Los Gatos property? Call (650) 405-3637 to schedule your free estimate. We’ll deliver a flat written price with a written scope and a written warranty - before anyone picks up a tool.
Written by Grant Rowan, Owner at Rowan Construction Group, serving Los Gatos since 2007.