If you're planning an ADU in Eugene, there's one decision that will affect your timeline, your budget, and the long-term livability of your new space more than almost any other. It's not the floor plan. It's not the finishes. It's your electrical panel.
Most homeowners don't think about this until someone raises it mid-project. By then, the options are more expensive and the timeline has already slipped. After decades as a licensed electrician and builder in Oregon, I've watched this scenario play out more times than I'd like to count. The good news is that it's entirely avoidable — if you address it before you break ground.
What an ADU Actually Adds to Your Electrical Load
An accessory dwelling unit is, functionally, a second home on your property. It needs its own lighting, outlets, heating and cooling, kitchen appliances, and often a washer and dryer. That's a significant addition to the electrical demand your property is already placing on your main service.
Older Eugene homes — particularly those built before the 1980s — frequently have 100-amp main panels. That was adequate when the house was built. It is often not adequate when you add an ADU. A modern ADU typically requires its own subpanel, and whether your existing service can support that subpanel without an upgrade depends entirely on what's already running through your main panel.
The Subpanel Question
Every ADU needs a dedicated subpanel. This is not optional — it's how the ADU's electrical system is isolated, metered if necessary, and kept safe. The subpanel feeds off your main panel, which means your main panel has to have the capacity to support it.
Sizing that subpanel correctly requires a load calculation — an actual accounting of what electrical demand your main house is running and what the ADU will add. This is technical work that requires a licensed electrician. It is not something to estimate or skip.
When it's done right at the beginning, a subpanel is a straightforward part of the project. When it's overlooked, it becomes an expensive surprise that can halt construction while you wait for an electrical upgrade and a new inspection.
🔌 Common Questions About ADU Electrical Panels
Do I need a subpanel for my ADU in Eugene?
Yes. Every ADU requires its own dedicated subpanel. This isolates the ADU's electrical system from the main house, allows for separate metering if needed, and is required by Oregon electrical code. The subpanel is fed from your main panel, which must have sufficient capacity to support the additional load.
How do I know if my main panel needs to be upgraded before building an ADU?
A licensed electrician should perform a load calculation on your existing service before your ADU project is quoted. If your home has a 100-amp main panel — common in Eugene homes built before the 1980s — there is a good chance an upgrade to 200-amp service will be required. This should be identified and priced before you sign a contract, not discovered mid-project.
How much does an electrical panel upgrade cost for an ADU project in Oregon?
Panel upgrade costs vary depending on the age of your existing service, the distance from the utility connection, and local utility requirements in Lane County. In Oregon, a service upgrade from 100-amp to 200-amp service typically runs between $1,500 and $4,000, including permits and inspection. This cost should be factored into your overall ADU budget from the beginning.
What This Means Before You Sign a Contract
Any contractor quoting your ADU project should be reviewing your main panel as part of their site assessment — not as an afterthought. If a quote lands in your inbox without any mention of your electrical service capacity, that's a gap worth asking about directly.
At Red Umbrella, electrical planning is built into every ADU assessment from day one. It's not a separate conversation or a line item that gets added later. After spending decades as a working electrician before transitioning to general contracting, I can tell you that the panel decision is one of the few things in a construction project that genuinely has to be right before anything else can move forward.
Get it right early. Everything else gets easier.
Thinking about an ADU on your Eugene property? Let's start with a site assessment — including your electrical service. Contact Red Umbrella here.
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