Planning an ADU? Here’s Your Essential Electrical Checklist

Building an Accessory Dwelling Unit (ADU)—whether it’s a “mother-in-law” suite, a backyard cottage, or a basement apartment—is an exciting way to add value to your property. But before the walls go up and the flooring goes down, there is a lot of electrical planning to do.

Most homeowners don’t realize the electrical scope of an ADU until they are already mid-project. To help you avoid expensive surprises, here is the ADU electrical checklist you need before breaking ground.

Separate Meter vs. Shared Service: Which Is Right for You?

One of the first big decisions you’ll face is how the ADU will get its power. This isn’t just about wires; it’s about how you plan to use the space.

Separate Meter

• What it is: The ADU gets its own utility bill and its own meter pack installed outside.
• The Benefit: If you are renting the unit out, a separate meter makes utility billing a breeze. It also adds more value if you ever decide to sell.
• The Catch: This usually involves more coordination with the local utility company and higher upfront costs for a new service feeder.

Shared Service (Sub-Panel)

• What it is: The ADU runs off a “sub-panel” connected to your main house’s electrical panel.
• The Benefit: This is often cheaper and simpler to install during construction.
• The Catch: It’s much harder to track exactly how much electricity the ADU tenant is using. Plus, you have to make sure your main house panel has enough “room” (capacity) to share.

Navigating the ADU Electrical Permit Process

You might be a handy DIYer, but an ADU is a complex legal structure. In most places, including the Portland area, you cannot legally do your own electrical work on a secondary dwelling unit.

• Building vs. Electrical Permits: Often, your electrical permit is tied to your master building permit. You can’t get your final “Certificate of Occupancy” without a signed-off electrical inspection.
• The Rough-In Inspection: This happens after the wires are pulled but before the drywall goes up. If you miss this window, you might have to tear down walls to show the inspector your work.
• Professional Requirement: Because ADUs are often used as rentals, local jurisdictions require a licensed electrician to pull the permits and perform the work to ensure it meets strict fire and safety codes.

Common ADU Electrical Mistakes (and How to Avoid Them)

Small mistakes early on can cause massive delays for your plumbers, painters, and carpenters later.

1. Skipping the Load Calculation: Before you add a whole new living space, you must calculate if your main house’s service can handle it. Adding a stove, water heater, and AC to an already full panel is a recipe for blown breakers.
2. Under-Sizing the Sub-Panel: Even if the ADU is small, think about the future. Will the tenant want an EV charger? Will you add a heat pump later? Installing a panel with a little extra room now saves you thousands later.
3. Bad Timing: If the electrical rough-in isn’t scheduled correctly, it can stall the entire project. The electrician needs to be in and out before the insulation and drywall crews can even start.

Making Your ADU Project a Success

Building an ADU is a big investment, and getting the electrical right from the start is the best way to protect that investment. From choosing the right meter to passing your inspections, having a clear plan makes the whole process smoother and less stressful.

At Electric Avenue LLC, we love helping homeowners in the Portland metro area, including Clackamas, Multnomah, and Washington County, bring their ADU dreams to life. We’re a family-owned business, and we specialize in making the technical side of construction easy to understand.

Starting an ADU project? If you need a professional to look at your plans, perform a load calculation, or handle the wiring from start to finish, we’re here to help. Reach out to us for an estimate, and let’s get your new space powered up the right way.