Portland’s Accessory Dwelling Unit Laws: Building a Rental ADU in 2025

Aug 12, 2025 | Insights

A tiny home in a backyard that would make a perfect rental ADU

As Portland grapples with housing shortages and rising rental costs, Accessory Dwelling Units (ADUs) have emerged as a flexible, homeowner-friendly solution. Recent zoning reforms have made it easier than ever to build an ADU as a long-term rental, a multigenerational living space, or a supplemental income source. With favorable legislation like the Residential Infill Project (RIP1 and RIP2) and statewide housing support, Portland is leading the way in ADU adoption. So, if you’re a Portland resident contemplating a rental ADU on your property, is now the time to act? Read on to find out.

Evolution of the Law: RIP1, RIP2 and Beyond

Portland has steadily embraced ADUs to address housing shortages and encourage urban density. Residential Infill Project Parts 1 and 2 have significantly reshaped local ADU rules in recent years.

Key changes include:

  • Double ADUs: You can now build up to two ADUs on a single property, including configurations combining both in a single detached building.
  • No mandatory parking: Off‑street parking requirements have been eliminated, meaning that existing driveways can be repurposed (though removing curb cuts is required).
  • Simpler accessibility: Only one of the structures (a house or an ADU) requires wheelchair-friendly features. Basements and steep lots may be exempt from this requirement.
  • Design flexibility: Detached ADUs are allowed beside duplexes, basement ADUs can reach up to 1,000 sq ft (up from 800), and street-facing entrances are permitted.
  • Broader zoning: RIP2 expanded eligibility to larger lots in outlying zones (R10, R20), cottage clusters, and duplex ADU combos.

These updates position Portland as a national leader in ADU-friendly policy.

The Benefits of Having a Rental ADU

For starters, why would you want to build an ADU on your property? Although it’s a significant undertaking and requires a substantial investment of time and money, the results can be more than worth it. These units offer their owners increased flexibility, tax benefits, and additional income opportunities.

1. Stable Income and Asset Appreciation

A Rental ADU can yield steady monthly cash flow. A well-located ADU in Portland’s hot rental market can significantly augment household finances. And when well-designed, ADUs generally appreciate property value.

2. Multi-Purpose Flexibility

ADUs can house family members, guests, or pivot between uses, such as renting long-term or hosting extended relatives. Some homeowners even live in the ADU while leasing the main house.

3. Critical Housing Solutions

With Portland’s high demand for housing, ADUs help create affordable, smaller-scale units without altering neighborhood character, thanks to modest size and streamlined regulations.

4. Tax and Fee Savings

System Development Charges (SDC) waivers and other incentives help reduce upfront costs—a key factor for many owners.

Building Permits, Standards & Infrastructure

Before jumping into construction, homeowners must navigate permits, codes, and utility protocols. Ensure you have these permits before you begin:

  • Building permit (essential for any structural changes).
  • Electrical, plumbing, and mechanical permits.
  • Pre‑approved ADU drawings are available for faster approvals.

Construction Standards

Building a new ADU means staying in line with a number of requirements before, during, and after the construction process. Here are a few to keep in mind:

  • Compliance with the Oregon Residential Specialty Code: Egress windows, ceiling heights, fire barriers, insulation, and wheelchair‑friendly entries (for at least one unit).
  • Zoning design rules: Coverage maxes out at 75% of the main dwelling’s living area or 800 sq ft (unless the ADU is in a larger basement). The unit must also meet setback requirements, open‑space rules, and avoid front‑yard placement.
  • Utility connections: Water/sewer may be shared or separate, depending on the fixtures. A hazardous-site review (flood, steep slope, landslide) and soil report may be required according to your intended location.

Fees and Exemptions

Building permits and SDCs apply, but SDC waivers are available if the ADU is not used for short‑term rentals (STRS) for 10 years. Additionally, Portland recently offered up to $15,000 incentive if the owner commits to long-term rentals and no short-term rentals.

State-Level Support and Oregon Context

Oregon’s statewide zoning reforms complement Portland’s local efforts:

  • HB 2001 (2019): Allows missing‑middle housing (duplexes, triplexes, fourplexes, cottage clusters) on single-family lots in cities of over 25,000 people.
  • SB 458 (2021): Requires permission for lot divisions.
  • Further legislation (SB 1537, HB 2138): Continues to expand housing options and mandates local updates—middle housing adoption by 2027; removes private covenants restricting ADUs retroactively, starting in 2027.

This second wave of reform syncs municipal and state goals: densify, de‑single-home‑zone, and ease ADU development.

Legally Creating a Rental ADU in Portland: A Step-by-Step

Turning your ADU into a leased unit requires more than a “For Rent” sign. There are legal guardrails to follow:

1. Fulfill the ADU Permit and Construction Checklist

Ensure that all building, trade, and ADU zoning permits are complete and have a certificate of occupancy.

2. Choose the Rental Type

  • Long-term rental: Any lease lasting more than 30 days. If you accepted an SDC waiver or incentive, you must commit to a covenant forbidding short-term rentals for 10 years.
  • Short-term rental: As a Type A or B accessory short-term rental, subject to zoning rules and permits. SDC-waived units cannot be STRs.

3. Register and Comply with Regulations

  • For long-term rentals: Register with landlord licensing and follow rent control rules. Portland landlords must comply with statewide rent caps (e.g., 10% annual increase for 2025) and may file for an ADU relocation-assistance exemption (if the owner occupies the site).
  • For STR: Obtain a Type A/B short-term rental permit and follow tourist tax and zoning limitations.

4. Maintain the Unit

Ongoing inspections, utilities upkeep, insurance, occupancy limits, and rental agreements must be managed carefully to comply with the law.

How Property Managers Can Help

Building a rental ADU is an exciting endeavor, but there’s no denying that it takes a lot of work. For someone looking to make some extra rental income without a background in construction or permitting, the process can feel overwhelming. Luckily, a seasoned property manager can ease the entire process through regulatory compliance, tenant handling, financial oversight, and operational efficiency.

At Rent Portland Homes Darla Andrews’ Office, our experienced team ensures your rental ADU meets all legal requirements and performs at its highest potential. Let us handle the complexities while you reap the rewards. Contact us today at (503) 515-3170 or reach out on our website to start your ADU rental journey.