ADU timelines disappoint people for one reason: the visible part (construction) is shorter than the invisible parts (planning and permitting). Here is the realistic sequence.
Phase 1: Feasibility and decisions (days to a few weeks)
Before anything else, confirm what you can build. A free assessment checks your local rules in minutes; a $349 Engineer Review gives you professional, property-specific confirmation. The most expensive timeline mistake is committing to a plan your jurisdiction will not approve.
Phase 2: Plans and engineering (days to weeks)
Complete permit-ready plan sets do not take months to prepare when they are built from proven designs. QuiPlans delivers permit-ready packages in 10–14 days on the standard tier, 7–10 days priority, and 3–5 days express. Custom designs take longer.
Phase 3: Permit review (weeks to months)
Your city reviews the drawings for code compliance. Simple projects in ADU-friendly jurisdictions can clear in a few weeks; complex reviews or busy departments can take a few months. Incomplete or non-professional drawings are the single biggest cause of multi-cycle rejections — each resubmission cycle adds weeks. This is where complete, engineer-prepared packages earn their cost back.
Phase 4: Construction (several months)
Once the permit is issued, a detached ADU typically takes several months of active construction — longer in bad-weather seasons or with contractor availability constraints. Garage conversions are usually faster because the structure exists.
Where projects actually lose time
- Incomplete drawings causing permit resubmission cycles
- Utility connection approvals discovered late
- Changing the plan mid-permit (each change can restart review)
- Seasonal construction windows missed by a late permit
The common thread: the timeline is decided mostly before construction starts. Feasibility first, complete drawings second, and the rest of the calendar takes care of itself.
