Accessory Dwelling Unit Design and Architecture
Tweto Architecture has maintained a strong focus on Accessory Dwelling Units (ADUs) since its founding. Through the design of more than a dozen ADU projects, the firm has developed practical expertise across a range of ADU types, including detached ADUs, attached ADUs, basement conversions, and garage conversion projects.
For those unfamiliar with ADUs, they represent a legal path to creating an additional dwelling unit on most residential properties in Portland, Vancouver, Bend, and surrounding areas. Rules vary by jurisdiction, but most place limits on size — typically around 800 square feet — as well as lot location and appearance. In most cases, an ADU shares utility connections with the existing home. A completed ADU can function as an independent home or apartment, with a kitchen, bathroom, living space, and one or more bedrooms.
Common Uses and Benefits of ADUs
Building an attached or detached ADU can be a practical way to add flexible living space to a property. Common uses include:
- Multi-generational living, such as an in-law suite or granny flat
- Long-term rental units
- Short-term rentals (e.g., Airbnb)
- Home offices or art studios
- Guest houses or backyard cottages
The relatively small size of an ADU, combined with the absence of separate land costs, potential development fee waivers, and shared utilities, can make them a more affordable option for adding housing in urban areas where development is otherwise challenging. Their intended use can also evolve over time, offering long-term flexibility for homeowners.
In Portland specifically, ADUs are permitted in all residential zones. In many cases, more than one ADU can be added to a single property. Recent regulatory changes have also expanded what is possible — including allowing the demolition of accessory structures such as garages to make way for new ADU construction, and permitting ADU development within certain historic districts, including the Irvington Historic District, without requiring a full historic review.
Expanded Housing Options Under New Zoning Rules
Beyond ADUs, recent zoning code changes in Portland and surrounding areas have introduced additional housing options for many properties. These include the ability to split existing homes into duplexes, create detached ADU structures, and develop new triplexes, duplexes, and fourplexes on qualifying lots.
Tweto Architecture works with property owners to evaluate which options best align with their specific property conditions and project goals. As an experienced ADU contractor and design firm, they can help navigate the regulatory landscape and identify the most suitable path forward for a given site.
