Your Neighbor Just Built a Backyard Cottage. Here's What That Actually Takes.

The call comes in some version of this every few months: "My neighbor just finished a backyard cottage and is renting it for $1,600 a month. Can we do the same thing?"

Usually, yes. Portland is one of the most ADU-friendly cities in the country, and Oregon's statewide zoning reforms have made it even more accessible in recent years. But there is a meaningful gap between "it's possible" and "here's what it actually involves," and I have watched too many buyers and sellers get surprised by that gap.

So here is the real picture.

What We're Actually Talking About

An ADU (Accessory Dwelling Unit) is a second dwelling unit on a residential lot. They come in a few forms, and the form matters because the cost, timeline, and rules are all different.

A detached ADU is a separate structure: the classic backyard cottage, a garage conversion, or a new build on a lot with enough room. These are the most flexible and often the most valuable, but also the most expensive.

An attached ADU is an addition to the main home, like a finished basement with its own entrance, a converted bonus room, or an in-law suite. Less construction-intensive than a full detached build, but still a real project.

A Junior ADU (JADU) is a smaller unit fully within the existing structure, typically under 500 square feet. Portland allows these on most lots and they can often be created with less permitting complexity than a full ADU.

What Portland's Rules Actually Allow in 2026

Portland allows ADUs by right on most residential lots. You do not need a special variance or neighborhood approval in most cases, which is significant.

The key limits: detached ADUs can typically be up to 75% of the primary home's footprint or 800 square feet, whichever is larger. Portland's rules here are more generous than most cities. Height is generally limited to 18 feet for detached structures, with some zones allowing 25 feet, which opens the door to two-story ADUs.

One advantage Portland specifically: the city does not require additional off-street parking for most ADUs. If you have a tight urban lot, this matters.

A building permit is required. Plan review timelines through Portland Bureau of Development Services currently run roughly 6-12 weeks, though that varies depending on application completeness and current queue length.

The Cost Reality

This is where the range is wide, and I want to be straight with you about it.

Garage conversions tend to run $80,000 to $150,000. Basement conversions are often $60,000 to $130,000. A new detached ADU built from the ground up is typically $150,000 to $300,000 or more.

That range reflects differences in size, finish level, site conditions, whether utilities need significant upgrades, and current contractor pricing. The low end of any range tends to assume few surprises. The high end assumes real-world conditions.

Financing the Build

If you have equity in your home, a HELOC is often the most accessible path. It is flexible, usually lower-cost than construction financing, and allows you to draw funds as you need them.

Cash-out refinancing replaces your existing mortgage with a larger one and puts the difference in your pocket. This works best when current rates are competitive with what you already have.

Construction-to-permanent loans finance both the build and the long-term mortgage together. More complex, but useful for larger projects where you do not have enough equity to use a HELOC.

Oregon Housing and Community Services has offered ADU-specific loan products for income-qualifying homeowners in the past. The availability of these programs changes. If you want a current read on what is out there, ask me.

Buying a Home That Already Has One

If you are buying a property with an existing ADU, the key questions are: Is it permitted? How is the utility setup structured? How separately metered is it? What is realistic rental income in that specific neighborhood?

Unpermitted ADUs are common and are not necessarily dealbreakers, but they come with considerations around insurance, lending, and future liability that you should understand before making an offer.

For Families, Not Just Landlords

A lot of the people I work with on ADU transactions are not thinking about rental income at all. They want the ADU for a parent, an adult child, or a live-in caregiver. That context changes what you are looking for in a property and how you evaluate the options.

Portland has real inventory of homes with existing ADUs, homes with strong ADU potential, and lots where the square footage and configuration make a future build genuinely feasible. Finding the right fit requires knowing what you are looking for before you start searching.

If you want a property-specific read on ADU potential, or help thinking through a build you are considering, get in touch. 503-544-5722 or the contact page.