Accessory Dwelling Units (ADUs) are one of Portlands most popular home improvementsoffering flexibility, rental income, and multigenerational housing solutions. But homeowners often face a key question: should you build a basement ADU or invest in a detached unit? Lets break down the pros, cons, and key considerations for each to help you decide which type of ADU is best for your property.
What Is a Basement ADU?
A basement ADU is a fully functional apartment built into the lower level of your existing home. It includes its own entrance, bathroom, kitchen, and living areaand is separated from the main home through a private stairwell or exterior access point.What Is a Detached ADU?
A detached ADU (also known as a backyard cottage or guest house) is a standalone structure typically built in the backyard. It has complete independence from the main house, both structurally and in terms of utilities.Basement ADU: Pros and Cons
- ? Lower Construction Costs: No need for a new foundation or roofing system
- ? Quicker Permitting: Often less complex than detached builds
- ? Great for Long-Term Guests or Family: Offers privacy with proximity
- ?? May Have Limited Natural Light: Requires smart lighting and window placement
- ?? Ceiling Height Requirements: Portland code requires at least 68 finished height
Detached ADU: Pros and Cons
- ? Total Privacy: Ideal for rental income or guest stays without noise overlap
- ? Design Freedom: Customize floorplans and architecture from scratch
- ?? Higher Costs: Requires new foundation, utilities, and exterior finishes
- ?? May Trigger Additional Zoning Review: Especially in Portlands overlay zones