ADU construction in Portland

Portland is one of the most ADU-friendly cities in the country, and a well-built accessory dwelling unit is one of the highest-value additions a homeowner can make — for rental income, family, or flexible space. But ADUs are full buildings in miniature, with their own foundation, utilities, and permitting. This guide covers what a Portland ADU contractor actually has to navigate.

Detached, attached, or conversion

There are three broad paths. A detached ADU is a standalone cottage in the backyard — the most flexible and private, and usually the most expensive. An attached ADU adds living space onto the existing house, sharing a wall and some systems. A conversion turns an existing basement, attic, or garage into a legal dwelling, often the most cost-effective when the bones allow it. The right choice depends on your lot, your budget, and how you intend to use the space.

Zoning, SDCs and the permit path

Portland allows ADUs on most residential lots, with size, height, and setback limits that vary by type. The city has historically waived or reduced System Development Charges for ADUs — a meaningful savings — though these policies change over time. Because the rules are specific to each lot and current code, the value of an experienced local ADU contractor is real: they confirm what your property allows before you fall in love with a plan that won't pencil.

Site conditions drive the budget

On paper, two ADUs of the same size can cost very differently. Access for equipment, how far utility connections must run, slope and soil, and tree protection all affect the number. Portland's hilly West Hills lots, for example, often carry higher site costs than a flat lot in Woodstock or Richmond. A good contractor surfaces these realities early rather than in a change order.

Designing a small space that lives large

The best ADUs feel generous despite their footprint — through ceiling height, daylight, built-in storage, and an efficient plan. Because the unit is small, every material and detail is visible, so finish quality reads loudly. This is where design-build experience pays off.

Cost and timeline

A high-quality detached ADU in Portland generally runs from roughly $250,000 to $450,000 or more; conversions can cost less. Expect 6–12 months from design through construction, with permitting and site complexity as the main variables.

ADUs often accompany a larger whole-home renovation, and the same care shows up in our kitchen and bathroom guides. To see what your lot allows, LUX Construction can help — start on our contact page.