Portland ADU Guide & Resources
Permitting & Development Reference
Building & Converting an ADU in Portland, Oregon
A complete guide to the zoning, building-code, permitting, and fee requirements for accessory dwelling units — for homeowners and contractors.
An accessory dwelling unit (ADU) is a smaller, fully independent home on the same lot as an existing house, attached house, duplex, or manufactured home. It must include its own provisions for living, cooking, eating, sleeping, and sanitation, and may have a separate exterior entrance. This guide covers the main requirements for both new / detached builds and conversions of existing space.
- Where ADUs are allowed & how many
- Size limits
- Height, setbacks & placement
- Visitability & accessibility
- Building-code & construction standards
- Illustrated conversion sketches
- Permits & who can do the work
- Fees & System Development Charges
- Utilities, address & more
- Adjustment review
1 Where ADUs Are Allowed & How Many
ADUs are permitted by-right (no land-use hearing) in most residential zones and several others. They may be located within a house, attached to it, or built as a detached structure.
Permitted base zones: Single-dwelling (RF, R20, R10, R7, R5, R2.5), Multi-dwelling, Commercial Mixed-Use, and Central Employment (EX).
Number of ADUs per lot
- One ADU on any lot with a house, attached house, or manufactured home that meets the minimum lot size.
- Two ADUs if the site fronts a City-maintained street, meets the larger minimum lot size, and is not in the Constrained Sites (“z”) overlay. Only one may be attached.
- One ADU with a duplex (must be detached from the duplex).
- ADUs cannot be combined with floating homes, triplexes, fourplexes, cottage clusters, or multi-dwelling structures.
Minimum lot size (single-dwelling zones)
| Zone | One ADU + attached house (Table 205-1) | Two ADUs, or duplex + ADU (Table 205-2) |
|---|---|---|
| R20 | 10,000 sq. ft. | 12,000 sq. ft. |
| R10 | 5,000 sq. ft. | 6,000 sq. ft. |
| R7 | 3,500 sq. ft. | 4,200 sq. ft. |
| R5 | 2,500 sq. ft. | 3,000 sq. ft. |
| R2.5 | 1,500 sq. ft. | 1,500 sq. ft. |
In multi-dwelling, commercial, and EX zones, two ADUs are allowed regardless of site size or street frontage. Look up your zone at PortlandMaps.com.
2 Size Limits
The maximum ADU size is 75% of the living area of the main house, or 800 square feet — whichever is smaller.
Basement exception: The size limit does not apply when the ADU is in the basement of a primary structure that is at least five years old.
“Living area” excludes: the thickness of exterior walls; garage areas; basement areas with ceilings under 6 ft 8 in; and any area where floor-to-ceiling height is under 5 ft or that is not reachable by a stairway.
3 Height, Setbacks & Placement Detached
Height
- 20 ft max outside required setbacks.
- 15 ft max inside required setbacks.
Building coverage
- A detached ADU’s footprint cannot exceed that of the primary structure.
- All detached accessory structures together: no more than 20% of the site.
Location / setbacks
- Must sit 40 ft back from the front lot line, or behind the rear wall of the main house.
- Side and rear setbacks start at 5 ft; may be larger by zoning.
Parking
- No additional on-site parking is required.
Exterior design standards (detached ADUs taller than 15 ft)
The ADU must visually relate to the primary house. Each element must either match the house or meet the stated minimum:
| Element | Requirement |
|---|---|
| Finish materials | Match the house, or use an approved material: wood, composite board, vinyl, or aluminum |
| Siding pattern | Shingle pattern, or horizontal clapboard/shiplap with boards 6 in or less wide |
| Roof pitch | Match the house, or be at least 6/12 |
| Trim | Match the house, or be at least 3.5 in |
| Eaves | Match the house, or be at least 1 ft |
| Window orientation | Match the house, or be square or vertical |
4 Visitability & Accessibility
When building two ADUs on a lot with a house, or one ADU on a lot with a duplex, at least one unit must be “visitable” for wheelchair users: zero-step access and entrance, an accessible bathroom, accessible living area, and compliant doors (Ref. 33.205.040.C.5).
5 Building-Code & Construction Standards
The applicable construction code depends on the project type:
| Project type | Governing code / guide |
|---|---|
| New detached ADU | Oregon Residential Specialty Code (ORSC) |
| ADU addition to a single-family dwelling | Oregon Residential Specialty Code (ORSC) |
| ADU conversion of existing space | Portland Building Code Guide 00-10 (ADU Code Guide) |
| ADU addition to / conversion within a townhouse | Portland Townhouse Code Guide 19-11 |
Key habitable-space minimums Critical for conversions
Existing attics, basements, and garages frequently fall short of code. The most common deal-breakers:
| Requirement | Standard |
|---|---|
| Ceiling height (habitable rooms) | Min. 7 ft (limited exceptions allow 6 ft 8 in for portions of converted nonhabitable space) |
| Emergency egress window (sleeping rooms) | Min. net clear opening 5.7 sq ft (5.0 sq ft at grade); min. 24 in high & 20 in wide; sill no higher than 44 in |
| Egress / emergency escape | Each sleeping room needs a door or window opening directly to the exterior |
| Insulation & ventilation | Must meet current energy code; an energy-conservation measure must be selected |
| Stairs | Must meet ORSC rise/run, width, and guard/handrail standards |
| Smoke & CO alarms | Required throughout per current code |
✎ Illustrated Conversion Standards
For conversions of attics, basements, and garages, Portland allows special alternative standards for existing space. The sketches below — reproduced from the City of Portland’s Brochure #9: Converting Attics, Basements and Garages to Living Space — illustrate the key dimensional rules for stairs, attics, basements, and egress windows.
Sketches reproduced from the City of Portland’s Brochure #9. Refer to the brochure and the Oregon Residential Specialty Code for the complete standards, exceptions, and details.
6 Permits & Who Can Do the Work
Every ADU — new or converted — requires a building permit, plus separate trade permits for electrical, plumbing, and mechanical work. Trade permits can be filed with the building permit (single permit number) or later.
- Contractors must hold a current Oregon CCB license; the CCB number must be on the application before a permit issues.
- A homeowner may do and sign for their own building and trade work — except electrical, which must be done by a licensed electrical contractor on an ADU.
- Verify permit history first. Any prior unpermitted work must be permitted as if new. Don’t rely on county tax records.
Required submittals
- Building permit application + site plan
- Full construction plans, or one of the City’s four free pre-approved ADU plans (gable/shed roof × slab/crawlspace) — note “Pre-Approved ADU” on the application
- Stamped truss package if using engineered trusses (may be a deferred submittal)
- Building permit application
- Site plan
- Architectural plans
- Structural plans (if structural changes are proposed)
Submit online through DevHub PDX. Large projects may qualify as a Major Residential Alteration & Addition (MRAA), which can trigger neighbor notification. Sites with slopes of 20%+ or in landslide areas require a geotechnical (soils) report; floodplain sites have added restrictions.
Permit process at a glance
- 1. Research — zoning, permit history, utilities, hazards.
- 2. Prepare — forms, site/floor/structural plans (optional free 15-minute reviewer appointments).
- 3. Apply — submit via DevHub; respond to any checksheet corrections.
- 4. Issue — pay all fees; permit is not issued until paid in full.
- 5. Build & inspect — complete required inspections, ending with a final approval.
7 Fees & System Development Charges (SDCs)
Budget for building permit fees, water-service fees, and System Development Charges — one-time charges that offset a project’s impact on City infrastructure. SDCs can add substantial cost.
| Charge | Notes |
|---|---|
| Building permit fees | Based on permit type, scope, valuation, and required reviews |
| Transportation SDC | Charged by PBOT unless waived |
| Environmental Services SDC | Sewer/stormwater; based on prior fees paid & current connection charge |
| Parks & Recreation SDC | Charged on any ADU unless waived |
| Water Bureau SDC | Only if the existing water meter must be upsized |
8 Utilities, Address & Other Considerations
- Water/sewer: An ADU may share the main dwelling’s connections or need its own, depending on fixture count and whether a septic system is involved. Upsizing a line or adding a separate connection adds fees even when SDCs are waived.
- Property taxes: An ADU raises home value and therefore property taxes — set by the county assessor (Multnomah/Clackamas/Washington), not the City.
- Addressing: The site keeps one street number; each dwelling gets a letter (A, B, C…) posted legibly at its entrance.
- Trees: Trees with trunks over 12 in require protection measures during construction; project value may trigger tree-planting requirements.
- Short-term rentals: An ADU may be a Type A (1–2 bedrooms) or Type B (3–5 bedrooms) accessory short-term rental with proper permits — subject to the 10-year SDC-waiver restriction above.
- Existing/illegal units: Former “Accessory Rental Units” (ARUs) are treated as ADUs and may be out of compliance; unpermitted units must be permitted, which can require exposing concealed work for inspection.
9 If You Can’t Meet a Standard: Adjustment Review
When a project doesn’t meet an ADU development standard, an Adjustment Review (Ch. 33.805) is required. It is a discretionary land-use review, takes roughly 8–10 weeks, is decided on the Chapter 33.805 criteria, and is not guaranteed to be approved.
Thinking about an ADU?
4P Renovations’ certified ADU specialists can answer your questions and help get your project scheduled. Reach out to get started.
Disclaimer & sources. This guide summarizes the main requirements for ADUs in Portland, Oregon and is for general planning purposes only; it is not a substitute for the full Zoning Code, building code, or professional advice. Requirements vary by property, zone, and overlay, and rules change — always verify your specific zoning at PortlandMaps.com and confirm current standards with City of Portland Permitting & Development (503-823-7300). Primary sources (current as of June 2026): Portland Zoning Code Chapter 33.205 (Accessory Dwelling Units); Portland.gov ADU zoning, permitting, and conversions pages; Portland Building Code Guide 00-10; Portland Brochure #9 (Converting Attics, Basements and Garages to Living Space); Oregon Residential Specialty Code.
Portland ADU Resource Guide