Bay Area ADU decision hub
Find ADU builders, understand costs, permits, plans, garage conversion options, and the right path before you hand anyone a construction budget.
Project paths
Detached, prefab, garage conversion, and design-build ADUs have different risks. Lumping them together is how homeowners get bad numbers.
Bay Area homeowners usually need an ADU builder or design-build team that can handle feasibility, drawings, permits, cost planning, and construction. If you do not have drawings yet, start with a feasibility and permit-plan review before requesting construction bids.
An ADU contractor is useful once the scope is buildable: drawings, site assumptions, utility path, structural requirements, and city review issues should be clear enough to price.
The right ADU company depends on your bottleneck: feasibility, drawings, permitting, prefab selection, garage conversion, or construction. Pick the company type before comparing brands.
Prefab ADUs can be a strong fit when the lot has access, utilities, and a model that matches the homeowner's needs. The hard part is often site-specific: foundation, utility trenching, crane access, fire access, and city permit coordination.
A garage conversion ADU may cost less than a detached new-build ADU, but the existing garage must still satisfy building, fire, energy, utility, ceiling height, moisture, and habitability requirements. Start with feasibility before pricing finishes.
A design-build ADU path can reduce handoff risk because feasibility, drawings, budget decisions, permitting, and construction planning are coordinated earlier. It still needs transparent scope, source-backed requirements, and honest cost ranges.
Cities
The launch city pages focus on San Jose, Santa Clara, and Sunnyvale first. More cities are in JSON without pretending thin pages are finished.
Featured providers
These profiles are local JSON records with source links and verification status. Clean data beats a made-up five-star badge every time.
Shortlist seed 91 ADU-focused design-build comparison benchmark
ADU-focused Bay Area company with public positioning around design, permitting, and building ADUs.
Partner disclosed 88 Budget-first ADU planning and design-build path
Budget-first South Bay and Peninsula residential design-build team positioned for ADU planning, permit drawings, garage conversions, and construction handoff.
Shortlist seed 78 Prefab ADU comparison
Prefab ADU provider with public Bay Area ADU builder positioning and manufactured-home style offerings.
Public source 78 Full-service ADU company comparison
Bay Area ADU provider publicly positioned around full-service ADU solutions.
Public source 77 Custom ADU and local design-build comparison
Bay Area design-build construction company with public ADU content and local construction positioning.
Public source 74 ADU coordination and contractor path comparison
Bay Area/Northern California ADU coordination provider with public positioning around ADUs, JADUs, additions, and contractor coordination.
Cost snapshot
Use these as planning ranges only. Site work, utilities, drawings, permits, and existing structure condition decide the real number.
| ADU path | Planning range | Notes |
|---|---|---|
| detached adu | $300,000-$600,000 | Planning range for Bay Area detached ADUs. Use only before site-specific feasibility, plans, utility review, and provider bids. |
| garage conversion | $120,000-$300,000 | Planning range depends heavily on slab, framing, fire separation, utilities, moisture, ceiling height, and city review. |
| prefab adu | $250,000-$500,000 | Planning range should include site work, delivery, foundation, utilities, permits, and finishes; prefab unit price alone is not enough. |
| junior adu | $60,000-$180,000 | Planning range for JADU-like internal conversions; city-specific rules and existing conditions drive scope. |
Guides
Bay Area ADU budgets usually move because of project type, square footage, site access, utilities, foundation, fire/life-safety requirements, finish level, city review, and whether drawings are already permit-ready.
adu cost bay area The MVP calculator is a planning-range estimator and lead form, not a fake precision machine. It asks for city, ADU type, size, drawings, permits, utilities, timeline, and budget stage.
adu cost calculator San Jose maintains dedicated ADU resources, including an ADU page, universal checklist, preapproved plans, FAQs, permit process material, and fire requirements. Use official city documents as the source of truth.
san jose adu requirements San Jose ADU permit cost depends on project size, scope, building permit fees, possible school fees, other city fees, utility requirements, and plan-correction complexity. Use official fee resources before relying on third-party numbers.
san jose adu permit cost Garage conversion permit cost is tied to whether the garage can legally become living space. The budget moves with structure, slab, moisture, fire separation, ceiling height, utilities, windows, energy code, parking, and plan corrections.
garage conversion permit cost Permit-ready ADU plans are not just a pretty floor plan. They usually need site-specific drawings, code notes, structural or energy documentation, utility information, and enough detail for city review.
permit ready adu plans