Quick Answer: A detached ADU in San Jose takes approximately 12-18 months from the start of design to final inspection in 2025. The timeline breaks down as: (1) Design and

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How Long Does ADU Construction Take From Start to Finish in San Jose 2025?

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Quick Answer: A detached ADU in San Jose takes approximately 12-18 months from the start of design to final inspection in 2025. The timeline breaks down as: (1) Design and plans: 6-12 weeks — hiring an architect or designer, measuring the property, drawing plans; (2) Permit application and plan check: 6-10 weeks (San Jose ADU ministerial review must be approved in 60 days per state law, but plan corrections can add time); (3) Construction: 4-8 months depending on ADU size and complexity — foundation (3-4 weeks), framing (3-4 weeks), rough MEP (4-6 weeks), insulation and drywall (3-4 weeks), finish work (6-10 weeks); (4) Final inspection: 1-2 weeks. Garage conversion ADUs are faster: typically 8-14 months total because there’s no new foundation.

ADU Construction Timeline by Phase — San Jose 2025

PhaseDetached ADUGarage Conversion
Design and architectural plans6-12 weeks4-8 weeks
City permit application and plan check6-10 weeks5-9 weeks
Site prep and foundation4-6 weeks0-2 weeks (slab drilling)
Framing3-5 weeks1-2 weeks
Roof / exterior sheathing / weatherproofing3-4 weeks1-2 weeks
Rough plumbing, electrical, HVAC4-6 weeks3-5 weeks
Rough inspection sign-off1-2 weeks1-2 weeks
Insulation, drywall, exterior finish3-5 weeks3-4 weeks
Finish work (cabinets, tile, fixtures)6-10 weeks5-8 weeks
Final inspection and certificate of occupancy1-3 weeks1-2 weeks
Total (from design start to move-in)12-18 months8-14 months

Quartz Construction manages the complete ADU design-to-build process in San Jose — minimizing delays through experienced permit coordination and a dedicated project management team. Learn about ADU construction services. CSLB #1003436 | Call (650) 749-7436.

How Long Does ADU Construction Take From Start to Finish in San Jose 2025?
How Long Does ADU Construction Take From Start to Finish in San Jose 2025?
How Long Does ADU Construction Take From Start to Finish in San Jose 2025?
How Long Does ADU Construction Take From Start to Finish in San Jose 2025?

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