An accessory dwelling unit, or ADU, is a smaller home on the same lot as a primary residence. In Portland, it can create a separate place for family, a rental home, or a way to make better use of a city lot. The right design starts with a more specific question than “Can I build an ADU?”: what should this home make possible, and what can the site support?
Start with the people who will use it
Decide who the ADU is for and how they will live there. A home for a parent may need an easy route from the street, a bedroom and bathroom on one level, or room for mobility equipment. A rental may call for clear separation from the main house, durable finishes, and storage for everyday items. A home for an adult child might need a balance between privacy and shared outdoor space.
Those choices affect the plan. A compact footprint can still feel generous when rooms receive good daylight, circulation is efficient, and storage is designed into the walls or furniture. Windows on two sides of a room, where the site allows, can make a small space feel more open. These decisions are more useful to settle early than adding square footage without a clear purpose.
Look at the lot before drawing the building
Placement depends on the shape and conditions of the property. Existing buildings, trees, slopes, access paths, utilities, and neighboring windows can all influence where an ADU fits. Zoning rules, setbacks, height limits, and other requirements also need to be checked for the specific lot. Portland’s rules and a property’s circumstances can change what is possible, so don’t rely on a neighbor’s project as a guide to your own.
Consider how people will get to the ADU, where bicycles and trash will go, and whether outdoor space still works for both homes. Think about privacy from nearby windows as well as the view from inside. A small change in orientation or window placement can help the new home feel connected to the site without putting every room on display.
Plan for costs and trade-offs
An ADU’s construction cost is not only the cost of its rooms. Site access, utility connections, foundation conditions, and the complexity of building around an existing house can affect the overall project. A rough cost needs to be considered alongside the household’s budget and the likely scope of work, not treated as a final bid.
Fold Architecture begins each project with a paid two-hour feasibility study that looks at what the lot and budget can support, including zoning, setbacks, and a rough construction cost. That early check can help clarify whether an ADU is a good fit and which compromises deserve attention. If you’re weighing an ADU for your Portland lot, get in touch to discuss a feasibility study.