How Long Does It Take to Build an ADU?

Adding an accessory dwelling unit (ADU) to your property is a smart investment—but it is not a fast one. From the first sketch to move-in day, most ADU projects take 10 to 18 months to complete. Timelines depend on your location, design, and how quickly permits are approved.

Let’s break down the typical ADU timeline by phase:

Phase 1: Planning and Design (6 Weeks to 4 Months)

This is where your ADU takes shape. During this stage, you will:

• Decide on layout, size, and type (attached, detached, or converted)
• Work with a designer or architect to develop plans
• Review local zoning codes and site restrictions

Custom designs or complex lots may extend this phase. Choosing a pre-approved ADU plan can speed things up significantly.

Phase 2: Permitting (3 to 9 Months)

Permitting is often the longest phase. You will:

• Submit detailed building plans
• Respond to comments or revisions
• Wait for final approval from your city or county

Turnaround times vary. Some cities issue permits within 2–3 months, while others may take 6–9 months, especially if zoning variances or design reviews are involved.

Phase 3: Site Preparation (2 to 4 Weeks)

Once permits are in hand, your property is prepped for construction. This step includes:

• Demolition (if needed)
• Site grading and clearing
• Running utilities and trenching
• Foundation work

This phase is relatively short unless you encounter underground surprises or utility issues.

Phase 4: Construction (4 to 12 Months)

This is the longest and most visible phase. It includes:

• Framing, roofing, siding, and insulation
• Electrical, plumbing, and HVAC installation
• Interior finishes: drywall, paint, flooring, and fixtures
• Final inspections and occupancy approvals

Smaller ADUs or prefab units may be completed in 4–6 months. Custom, two-story structures may take closer to 10–12 months.

What Can Speed Up or Slow Down the Process?

Several real-world factors influence your ADU timeline. These include:

• Design complexity: Simpler plans are faster
• Jurisdiction speed: Some cities are more efficient
• Prefab vs. stick-built: Prefabs save time
• Contractor availability: A reliable team keeps things on track
• Utility upgrades: Electrical panel or sewer changes add weeks

Bottom Line

Every ADU project is unique, but most fall within a 10–18 month window. The key to staying on schedule is working with experienced professionals and choosing designs that streamline approvals.

Want to Fast-Track Your ADU Build?

Explore pre-permitted, builder-friendly designs at adupatterns.com/collections/house-plan. The right plan can eliminate months of waiting and reduce permitting risks.