How Long Does It Take to Build an ADU? Your Step-by-Step Timeline

Ready to build an Accessory Dwelling Unit (ADU)? It’s an exciting move—whether you’re dreaming of extra space, rental income, or a cozy spot for family. But the big question is: How long is this going to take? On average, you’re looking at 6 to 12 months from start to finish, though it can vary depending on things like design, permits, and construction hiccups. Let’s walk through the steps so you know what to expect—and how to maybe speed things up!

ADU Construction Timeline: Step by Step

1. Planning & Research (1-2 Months)

Before you dive in, you’ve got some homework to do. This is where you figure out:

• What kind of ADU fits your place—detached, attached, garage conversion, or basement?

• What size and budget feel right for you?

• How will you pay for it—loans, grants, or tapping home equity?

✅ Pro Tip: Chat with an ADU expert like ADUnest early on—they can make this part a breeze.

2. Design & Architectural Plans (1-3 Months)

Once you’ve got a vision, it’s time to get it on paper. You’ll work with an architect or designer to:

• Check out your site and see what’s doable.

• Sketch blueprints and floor plans.

• Tweak things until they’re just right.

✅ Pro Tip: Some cities offer pre-approved ADU plans—grab those to skip a chunk of this wait!

3. Permitting Process (2-4 Months)

Here’s where patience comes in—permits can take time. You’ll need:

• Zoning Approval: Makes sure your ADU fits local land rules.

• Building Permits: Covers the nuts and bolts—structure, electrical, plumbing.

• Utility Permits: Needed if you’re adding new water or power lines.

In California, SB 1211 says cities have to process permits in 60 days, but some spots still drag their feet.

✅ Pro Tip: Team up with a permit pro to get your paperwork spot-on and avoid holdups.

4. Site Prep & Foundation Work (1-2 Months)

Permits in hand? Time to break ground! This step includes:

• Clearing out junk or old stuff.

• Digging and leveling the land.

• Pouring a foundation (for detached units) or shoring up what’s there (for conversions).

✅ Pro Tip: Go modular—prefab ADUs can skip a lot of this and go up fast.

5. Framing & Roofing (1-2 Months)

Now the ADU starts taking shape:

• Walls and roof go up.

• Windows and doors get added.

• Rough plumbing and wiring get threaded in.

✅ Pro Tip: Keep your contractor in the loop—good communication keeps things on track.

6. Interior Finishing (1-3 Months)

With the shell done, it’s time to make it homey:

• Insulation, drywall, and a fresh coat of paint.

• Flooring, cabinets, and fixtures go in.

• Final hookups for plumbing and electrical.

✅ Pro Tip: Pick pre-made kitchen or bath setups—they’re quicker to install.

7. Final Inspections & Approval (1 Month)

Almost there! The last hurdle is getting the green light:

• Structural & Safety Check: Confirms it’s built right.

• Utility Inspection: Makes sure power and plumbing are good to go.

• Occupancy Approval: Says, “Yep, you can live here!”

Pass these, and your ADU is ready to roll! 🎉

Total Time Breakdown

Stage	Estimated Time
Planning & Research	1-2 Months
Design & Plans	1-3 Months
Permitting	2-4 Months
Site Prep & Foundation	1-2 Months
Framing & Roofing	1-2 Months
Interior Finishing	1-3 Months
Inspections & Approval	1 Month
Total	6-12 Months

What Speeds Things Up—or Slows Them Down?

🔹 Ways to Move Faster:

✔ Stick with pre-approved plans.

✔ Hire a pro ADU contractor who knows the ropes.

✔ Choose a modular or prefab ADU.

✔ Double-check your permit paperwork before submitting.

⛔ What Might Stall You:

❌ Permit offices swamped with applications.

❌ Material shortages or shipping delays.

❌ Surprise issues with your foundation or site.

❌ Rainy days or bad weather slowing construction.

Can You Build an ADU Quicker?

You bet! Some ADUs wrap up in 4-6 months if you play it smart:

• Prefab ADUs: Built off-site and dropped in place in weeks.

• Garage Conversions: Less structural work means less time.

A simple site and smooth permitting can shave months off too.

Wrapping It Up: What’s Your ADU Timeline?

For most folks, an ADU takes 6-12 months to go from idea to move-in ready. It all depends on how tricky your project is. Plan ahead, team up with the right people, and pick efficient options, and you could be enjoying your new space sooner than you think.

Want to fast-track your ADU? ADUnest can help with everything from planning to permits—reach out today!

Got questions about ADU timelines? Drop them in the comments, answer will get back to you soon!