Accessory dwelling units come up constantly now: the basement apartment, the converted garage, the little cottage out back. They can genuinely change what you can afford. They can also be a permitting problem you inherited. The difference is entirely in the paperwork.
What Portland allows
Portland is unusually permissive, which is a large part of why you see so many. As of August 2026, ADUs are allowed across the residential zones, and standard single-family zones permit one ADU per house, either attached or detached. Detached units are capped at 800 square feet or 75 percent of the primary house, whichever is smaller.
Two rules matter more than people realize. There is no owner-occupancy requirement, so you can rent both units. And no off-street parking is required for an ADU, which is what makes many of these lots work at all.
There are system development charge waivers available, conditioned on the unit not being used as a short-term rental for ten years. If your plan involves short-term letting, that condition is not a footnote.
The question I ask first
Not "is there an ADU." It is: was it permitted, and does the paperwork exist?
Portland has a great many basement apartments and converted garages that were built by a previous owner over a weekend in 1998. They may be perfectly nice. They are also, on paper, sometimes not a dwelling unit at all. That affects what you can legally rent, what your insurer will cover, what an appraiser will credit, and what you can tell the next buyer.
I pull the permit history. It takes very little time and it is the whole difference between an asset and a liability.
Do not assume the lender counts the income
Buyers routinely build the rent into their affordability before talking to a lender. Whether and how much ADU income counts toward qualifying depends on the loan product, the documentation and the appraisal. Sometimes a good chunk counts. Sometimes none of it does.
Find that out before you fall in love with a house, not during underwriting. It is one phone call.
What it does to resale
A legal, permitted, well-built ADU widens your buyer pool: multigenerational households, people who want an office, people who want the income. An unpermitted one narrows it, because informed buyers discount it and their agents raise exactly the questions I am raising here.
If you are thinking of building one
Look at the lot before you fall for the idea. Setbacks, height limits, where the sewer runs, and whether there is genuinely a path to build. And talk to Portland Permitting and Development early, because the rules here have changed several times in the last decade and will change again.
The neighborhoods where I see this most are the ones with deep lots and older houses: Cully, St. Johns, and much of the streetcar-era eastside.
Zoning rules checked against portland.gov in August 2026. ADU rules in this city change often; confirm the current requirements for your specific address with Portland Permitting and Development before relying on any of this.
Quick answers.
Does Portland require the owner to live on site to rent an ADU?
No. As of August 2026 there is no owner-occupancy requirement, so both the primary home and the ADU can be rented. Confirm the current rule for your address before you build a plan on it, because this is exactly the kind of rule that changes.
How big can a detached ADU be in Portland?
Detached units are capped at 800 square feet or 75 percent of the primary house, whichever is less, with height and setback limits that vary by zone.
Can I count ADU rent toward qualifying for my mortgage?
Sometimes, and it depends on the loan product, the documentation and the appraisal. Never assume it. Ask your lender before you shop, because the answer changes what you can afford by a lot.
