If you’ve noticed more people turning to ADU builders in Portland than ever before, you’re absolutely right. The landscape has changed for these units, and for good reason. With rapid population growth, rising home prices, and the success of the Residential Infill Project, city planners have been revising old limitations and fine-tuning the details that still protect each neighborhood’s charm.
But homeowners are now asking the important question: What are the current rules for accessory dwelling units in 2025, how do they differ from past years, and what does it mean for you? We’ve answered these questions below!
There are many solid reasons to consider building an ADU, but it’s not unusual to feel a bit lost in the city’s code. Portland sets clear boundaries for these units, from placement and permits to size, height, and design.
When we compare past detached vs. attached ADU regulations, it’s no surprise that most homeowners opted for conversions rather than standalone structures. In 2025, however, building a separate unit on your lot is much easier. Here’s an overview of the rules and recent changes that have made this possible:
Under Portland ADU zoning rules, the city now allows up to two accessory units on a lot that already has a house, attached house, or manufactured home, as long as the site meets minimum lot size and fronts a city-maintained street. The exact requirements for the minimum size depend on the zone, which depends on the location. Remember, any detached ADU needs to be placed at least 40 feet back from the front lot line, or behind the rear wall of your main house.
New in 2025: The city has streamlined things by consolidating the two-ADU allowance and the 40-foot placement rule into a single, easier-to-read table within Chapter 33.205. The goal of this welcome change was to cut down on past ambiguities that often slowed down permit reviews.
What it means for you: The path to building two accessory units is now much clearer if your lot size and frontage qualify. It’s just important to get the site measurements early on to prevent any surprises once your designs reach the city reviewer.
When it comes to ADU permit requirements in Portland, all major home additions still require a mandatory building permit. You can submit the plans online for zoning and structural review, after which you schedule the necessary inspections. (Don’t worry, we handle this process for you.) Although System Development Charges (SDCs) can be substantial, a separate waiver can eliminate them if you record a 10-year covenant agreeing to ban short-term rentals on every structure on your lot.
New in 2025: The city has made applying for the SDC waiver much smoother with a new dedicated digital form, introduced in late 2024. This system is designed for quicker approvals, more straightforward instructions, and easier tracking of your application.
What it means for you: Dedicating your new unit only for long-term rental or family use can save you tens of thousands of dollars. Be sure to consider this 10-year covenant carefully if you have any thoughts of using platforms like Airbnb or VRBO for short-term stays in the future.
ADU size limitations in Portland generally set a firm cap at 800 square feet, or 75 percent of your primary home's living area – whichever figure is smaller. The only clear case where this doesn’t apply is basement conversions.
New in 2025: As a notable change, the city clarified that you can request an “Adjustment” review to exceed 800 square feet. Recently approved projects show that city staff are willing to approve designs up to around 1000 square feet when they meet specific design criteria and lot coverage rules.
What it means for you: If you have a standard plan for a detached unit that fits under 800 square feet, the review process is simple. But if your needs call for more space, you now have an option through this Adjustment review. Just remember that this may involve additional time for processing, as well as additional fees.
Regarding ADU height restrictions, the Portland city code says that detached units can rise to 20 feet if they’re outside of your property's setbacks. If the structure extends into the setback area, that height limit reduces to 15 feet, with an exterior wall height cap of 10 feet.
New in 2025: To make things easier, the city has updated the zoning code with more explicit language and simpler diagrams that clearly show how proximity to the lot lines influences allowable heights.
What it means for you: The added clarity makes it much easier for designers, builders, and homeowners to calculate the setbacks and allowed heights. This can save you from costly redesigns and frustrating permit delays.
ADU design standards in Portland only come into play when your unit exceeds 15 feet in height. At that point, a detached unit has to match your primary house through compatible siding and roofing, or with other types of pre-approved designs.
New in 2025: The city has now bundled all the design requirements into a single, comprehensive checklist on the design worksheet that reviewers can use. This eliminates much of the prior back-and-forth communication.
What it means for you: Make sure to follow this part of the regulations by aligning material choices early with your designer. Skipping this step can lead to additional design review processes and potentially significant delays for your permit.
As one of the biggest game-changers for ADU development, minimum off-street parking requirements no longer exist anywhere in the city. This means that you can remove any old driveways and expand your usable lot space, unless an existing land-use condition demands otherwise.
New in 2025: The core policy of no minimum parking was actually brought forth by RIP several years ago and is still firmly in place. However, the city has made a significant improvement this year by making the exact processes for legally removing parking spaces much clearer than they previously were.
What it means for you: It’s now much easier to free up space for an accessory unit on your lot by removing unused parking spaces and driveways. However, if you wish to keep your driveway, the curb cut still has to comply with current transportation standards.
At COOPER Design Build, we’re here to help you turn these newest ADU opportunities into real, livable space with a process that’s completely clear from the first sketch to the final walkthrough. Our team blends smart design and top-notch craftsmanship with smooth project management, so you can stay informed without getting buried in code jargon.
From Arlington Heights to the outer edges of the city’s area, we bring the same thoughtful care to every backyard build. Trust us to always listen first, tailor every inch to your vision, and keep the timeline on track. Ready to see how an accessory unit can work on your property? Contact us today and let’s get your project started!