How Long It Takes to Build Your ADU (and Why Utilities Matter)

We hope to see you soon!

NEXT STEPS - Thinking about your own ADU? Come chat with us this weekend about it! 

This weekend is the Idaho Remodeling & Design Show at the Boise Centre. Come chat with us at the Treeline Design & Build booth, we can even do a quick consult about your property and project idea! Looking forward to seeing you there. Use code IRS26 for a small discount on tickets. 

LEARNING THE BASICS - How Long Does It Really Take to Build an ADU?

Here’s a general idea of what to expect regarding timelines:

1. Feasibility & Design (4–8 weeks)
   We start with a site visit, zoning review, and design concepts. This phase is where we get creative, ensuring your ADU fits both your property and your budget.

1. Permitting (8–16 weeks)
   This stage can be a wild card and response times from the city building department can vary. We stay proactive, managing submittals and revisions to keep things moving.

2. Construction (16–24 weeks)
   Once we break ground, things move quickly. Foundation, framing, windows, roofing, siding, plumbing, electrical, HVAC, drywall, painting, cabinets, appliances, fixtures — it’s a lot of moving parts, but we’ve honed a predictable process to minimize surprises.

3. Final Inspections & Move-In (2–4 weeks)
   After construction, we coordinate all the final inspections, utility hookups, and finishing touches so your new ADU is move-in ready.

Total Typical Timeline: 7–12 months from concept design to completion

DEEP DIVE 

View fullsize

I want to do a "Deep Dive" into Utility Connections for ADUs
Connecting an ADU’s plumbing and power can be complicated. It’s important to note that utilities (water, sewer, electricity, gas, and internet) often add up to somewhere between 10-20% of the overall project costs, so planning early and choosing wisely can save time, money, and complications later!

1. Power:
An ADU can often share the main home’s electrical service — but if your existing panel is undersized, an upgrade might be required. Smart planning ensures enough capacity for future EV chargers or solar integration. If you’re considering using the ADU as a rental home, it’s worth evaluating whether or not you’d like to have a separate power meter in order to receive a separate utility bill.  It costs more, but it’s an important item to consider early on and think about your long term goals with the new house. 

2. Water & Sewer:
This can be a tricky piece. Detached ADUs will need separate trenches in order to connect the sewer and water lines. Early site evaluation helps avoid unexpected excavation costs. If you intend to rent the ADU, you may want to consider adding another meter so that the utility bill is separate, however it does cost more. 

3. Gas:
If your ADU will have gas appliances, we evaluate pressure and line sizing. Many homeowners now opt for all-electric systems for simplicity and energy efficiency.

4. Internet & Communication Lines:

Don’t overlook connectivity! A simple conduit run in an already-dug trench during construction saves time and money later.

Utility design happens when we’re sketching your floor plan and definitely before building plans are finalized. It affects layout, excavation and grading, and sometimes even the building  placement on the property. A good design-build team (like ours 🙂) integrates this early to prevent surprises. It’s easier, and cheaper, to build the utility design into the construction plan from very early on.  

All the best, 

Lindsay and Cody Wassard

Treeline Design & Build