Everything homeowners need to know about building an accessory dwelling unit in Portland - size limits, setbacks, permits, and the fee-waiver program that's helped make Portland one of the most productive ADU markets in the country.
Last verified: August 2026
9/10 · Very ADU-friendly
800 sq ft*
Max ADU size
20 ft
Max height
Not required
Owner-occupancy
By-right
Permit type
This page summarizes Portland's ADU standards under Portland City Code Title 33 (Planning & Zoning) for general reference - it is not legal advice. Regulations change; always confirm current requirements with Portland's Bureau of Development Services (BDS) before designing or applying for permits. See sources below.
Zoning & size requirements
What you're allowed to build
ADU type
Max size
Max height
Notes
Detached (new build or garage conversion)
800 sq ft or 75% of the primary dwelling's living area, whichever is smaller
20 ft outside required setbacks; 15 ft within them
Must sit 40 ft back from the front lot line, or behind the rear wall of the main structure
Generally the same 75%/800 sq ft formula; basement ADUs in homes at least 5 years old may be exempt from the cap
Same as primary structure
Common approach for basement conversions
Allowed zoning districts
ADUs are allowed in all of Portland's residential base zones citywide, and many single-dwelling lots that meet minimum lot size and street frontage can add two ADUs. Confirm your zone and lot eligibility with the Bureau of Development Services (BDS).
Additional standards
Setbacks, parking & other rules
Setbacks
Typically 5 ft at the rear; side setbacks vary by zone. Detached ADUs must sit 40 ft back from the front lot line or behind the primary structure's rear wall
Parking
No additional off-street parking required; Oregon state law (ORS 197.312) bars cities from requiring parking for ADUs
Units per lot
1 ADU allowed with most houses and duplexes; up to 2 ADUs allowed on qualifying single-dwelling lots with adequate lot size and street frontage
Owner-occupancy
Not required. Portland has had no owner-occupancy requirement since 2016, well ahead of Oregon's 2019 statewide mandate
Building code
Must meet Oregon Residential Specialty Code dwelling-unit standards
Rental license
No separate rental license is required for most long-term rentals; short-term rental use has its own city permit and is excluded from the SDC waiver program for 10 years if used
Ordinance history
How Portland's ADU rules got here
1998Early citywide adoption. Portland amended its code to allow ADUs citywide by right and dropped owner-occupancy and parking requirements, decades ahead of most large US cities.
2010Fee-waiver program launched. The city began waiving System Development Charges (SDCs) for qualifying ADUs, widely credited with kickstarting the wave of construction that made Portland a national ADU leader.
2016Owner-occupancy confirmed dropped. Portland's code carried no owner-occupancy requirement for ADUs, again well ahead of the eventual statewide mandate.
2019Oregon passes HB 2001. Signed August 8, 2019, the statewide law required cities over 2,500 people to eliminate owner-occupancy and parking requirements for ADUs by January 2020, building on 2017's SB 1051, which had already required cities over 2,500 to allow at least one ADU per single-family lot.
2021Residential Infill Project. Portland's RIP update went beyond the state mandate, allowing up to two ADUs on many single-dwelling lots alongside duplexes, triplexes, fourplexes, and cottage clusters.
Portland and Seattle are routinely cited as the two US cities building the most ADUs per capita, and Portland's early start is a big part of why - its SDC waiver program dates back to 2010, well before most other cities had usable ADU ordinances at all.
Permit process
How Portland ADU permitting works
1
Pre-application zoning check
Confirm your zone, lot size, and street frontage with the Bureau of Development Services (BDS) before designing, especially if you're hoping to add two ADUs.
2
Prepare your plan set
Site plan, floor plans, elevations, and structural drawings, plus floor plans of the existing house to verify the 75%/800 sq ft size calculation.
3
Apply for the SDC waiver (optional)
If you'll rent long-term rather than as a short-term rental for at least 10 years, apply for Portland's System Development Charge waiver, which can offset a large share of total fees.
4
Submit for permit review
File through Portland's online permitting system for zoning and building permit review; standard review commonly runs several weeks, longer if an Adjustment Review is needed.
5
Building permit & inspections
Once permits issue, begin construction and schedule the standard framing, plumbing, electrical, and final inspections.
6
Sign the SDC waiver covenant (if applicable)
Recorded against the property for 10 years, committing you not to use the ADU as a short-term rental during that period.
Fees, waiver terms, and review timelines change periodically - confirm current requirements with the Bureau of Development Services and the Revenue Division before applying.
Budgeting
What it costs to build an ADU in Portland
Garage conversion
Roughly $85,000-$170,000, the least expensive path since the shell already exists
Basement conversion
Roughly $120,000-$220,000, depending on existing ceiling height and utility access
New detached ADU
Roughly $170,000-$330,000+ for a code-compliant, fully finished freestanding unit
Permit & plan review fees
Typically a few thousand dollars for plan review and permits, separate from System Development Charges
System Development Charges (SDCs)
Can run $15,000-$37,000 if not waived; Portland's ADU SDC waiver can eliminate this cost in exchange for a 10-year no-short-term-rental covenant
These are general ranges from local contractor estimates and regional reporting, not quotes - actual cost depends on lot conditions, finishes, and whether you qualify for the SDC waiver. That waiver alone can be the difference between a large fee bill and a very small one, so it's worth applying for even if you're not certain you'll use it.
Before you apply
Tips for a smooth approval
Apply for the SDC waiver early. It can save $15,000-$37,000, but it requires a 10-year covenant against short-term rental use, so decide on your rental plans before you file.
Check if you qualify for two ADUs. Many single-dwelling lots with enough size and street frontage can add both an attached and a detached ADU - confirm eligibility with BDS before you design just one.
Verify the size formula against your actual house. The 800 sq ft cap only applies if 75% of your home's living area is larger - many homes are capped well below 800 sq ft.
Confirm setback placement before you site the building. A detached ADU generally needs to sit 40 ft back from the front lot line or behind your house's rear wall, which limits where it can go on narrow lots.
Ask about basement ADU exemptions. If your home is at least 5 years old, a basement conversion may be exempt from the standard size cap - worth confirming with BDS before you assume you're capped at 800 sq ft.
FAQ
Common questions
Do I need to live on the property to build an ADU in Portland?
No. Portland has had no owner-occupancy requirement since 2016, and Oregon's 2019 statewide law (HB 2001) locked that in for cities across the state.
How many ADUs can I build on one lot in Portland?
One ADU is allowed with most houses in most zones; qualifying single-dwelling lots with enough size and street frontage can add up to two.
Do I need extra parking for an ADU?
No. Oregon state law bars cities from requiring off-street parking for ADUs, and Portland doesn't require it.
What's the maximum size for a detached ADU?
800 sq ft or 75% of your primary home's living area, whichever is smaller, with a 20 ft height limit outside setbacks (15 ft within them).
How long does the permit process take?
Standard review commonly runs several weeks; projects needing an Adjustment Review can take roughly 8-10 weeks. Confirm current timelines with the Bureau of Development Services.
How much does an ADU cost to build in Portland?
Garage conversions run roughly $85,000-$170,000, basement conversions roughly $120,000-$220,000, and new detached units roughly $170,000-$330,000+, based on local contractor estimates and regional reporting - not counting System Development Charges unless waived.
What is Portland's ADU System Development Charge waiver?
A program that waives SDCs (commonly $15,000-$37,000) for ADUs rented long-term, in exchange for a 10-year covenant against short-term rental use.
Is Portland really one of the top ADU-building cities in the country?
Yes - Portland is consistently cited alongside Seattle as a national leader in per-capita ADU construction, helped by an SDC waiver program dating back to 2010.
Can I rent my ADU out on Airbnb or a short-term rental platform?
You can, but doing so within 10 years of receiving an SDC waiver violates the waiver covenant, and short-term rentals have their own city permit requirements - confirm current rules before you decide.
