ADU Building Guide for Portland Homeowners

Portland has some of the most progressive ADU (Accessory Dwelling Unit) regulations in the country. Here's everything you need to know about adding one to your property.

What Is an ADU?

An ADU is a self-contained living unit on your property — either attached to your home or built as a separate structure. It includes its own kitchen, bathroom, living space, and entrance.

Portland's ADU Regulations

Portland eliminated system development charges (SDCs) for ADUs, significantly reducing the upfront cost. Most residential lots in Portland can accommodate an ADU without a conditional use permit. Maximum size is generally 75% of the primary home's square footage or 800 sq ft, whichever is less.

Types of ADUs

Attached ADUs are built as additions to your existing home — converting a garage, adding a basement suite, or building a bump-out addition. Detached ADUs are standalone structures in your yard.

Typical Costs

ADU construction in Portland typically ranges from $150,000-$350,000 depending on size, finishes, and whether it's attached or detached. Detached ADUs with foundations and separate utility connections tend to cost more.

Timeline

Plan for 8-14 months from design to completion. The permitting process in Portland typically takes 4-8 weeks, and construction runs 4-8 months depending on complexity.

ROI and Rental Income

A well-built ADU in Portland can generate $1,200-$2,500/month in rental income, making it one of the best investments you can make in your property. Many homeowners recoup their construction costs within 5-8 years.