Everything homeowners ask about building an ADU in Portland — answered with 2026 data.
Yes, ADUs are allowed in Every residential zone (RF, R20, R10, R7, R5, R2.5 and the multi-dwelling RM zones) plus the commercial mixed-use and Central Employment (EX) zones, on a lot with a house, attached house, manufactured home or duplex (33.205.020). Not allowed with a triplex, fourplex, cottage cluster or multi-dwelling building. Check your base zone on the Portland Zoning App in Portland, OR. The maximum size for a detached ADU is 800 sq ft of living area or 75% of the main home's living area, whichever is less, measured after the ADU is built (33.205.040.C.1). Living area excludes exterior walls, garages and basement space under a 6 ft 8 in ceiling. Building coverage also cannot exceed the main house's, and all accessory structures together may cover at most 20% of the lot (33.110.245.C.3). Attached ADUs can be up to Same 800 sq ft / 75% cap as a detached unit; there is no separate attached or 1,000 sq ft limit. Exception: converting the basement of a house that has stood at least 5 years is exempt from the size cap entirely. Portland has an ADU-friendliness score of 9/10. Check our full Portland ADU rules page for complete zoning details.
ADU construction in Portland typically costs $180,000-$280,000. The cost per square foot averages $250-$400. Garage conversions are more affordable at $70,000-$160,000, while prefab ADUs cost $100,000-$240,000. Permit fees add Building permit and plan-review fees are valuation-based under the Building and Other Permits Fee Schedule effective July 10, 2026 (no flat ADU fee); trade permits are separate. SDCs: Parks $7,941 (under 700 sq ft) or $11,878, Transportation $3,421, waived with the 10-year no-STR covenant to your budget. See our detailed Portland ADU cost guide.
Detached ADUs in Portland can be up to 800 sq ft of living area or 75% of the main home's living area, whichever is less, measured after the ADU is built. Attached ADUs are limited to Same 800 sq ft / 75% cap as a detached unit; there is no separate attached or 1,000 sq ft limit. Exception: converting the basement of a house that has stood at least 5 years is exempt from the size cap entirely. Junior ADUs (JADUs) have a cap of N/A (Oregon and Portland have no junior ADU category; a unit inside the house is simply an ADU under the same 800 sq ft / 75% cap). Maximum height is Detached or connected ADU: 20 ft (33.110.245.C.1). A unit built inside a required side or rear setback in R7, R5 or R2.5 is limited to 15 ft with 10-ft walls. Detached units over 15 ft must match the house's siding, roof pitch (or use 6/12), trim, eaves and window orientation (33.110.245.C.4). An ADU inside or attached to the house follows the house's 30 ft zone limit. You are allowed up to 2 ADUs on a lot with a house, attached house or manufactured home; at least one must be detached, and in the R20-R2.5 zones the second needs Table 205-2 lot area and maintained-street frontage on a qualifying lot.
Rear setback: 5 ft in R7, R5 and R2.5; 10 ft in RF, R10 and R20 (Table 110-4). In R7/R5/R2.5 a detached ADU may sit on the rear lot line (0 ft) if it is at least 40 ft from the front lot line, no more than 15 ft tall with 10-ft walls, within a 24 x 24 ft footprint, has no doors or windows facing that lot line and keeps dormers 5 ft off it (33.110.245.C.2.b). Side setback: 5 ft in R7, R5 and R2.5; 10 ft in RF, R10 and R20 (Table 110-4). Same 0-ft exception as the rear yard for a detached ADU that is 40 ft back from the front lot line, 15 ft or lower, and shows no doors or windows to the neighbour; on a corner lot it must also be 20 ft from the side-street lot line (33.110.245.C.2.b). Front setback: A detached or connected ADU must be at least 40 ft from the front lot line or sit behind the rear wall of the main house (33.205.040.C.2). Zone front setbacks are 10 ft in R5 and R2.5, 15 ft in R7 and 20 ft in RF, R10 and R20; a garage entrance needs 18 ft (Table 110-4). Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
None. No additional on-site parking is required for an ADU (city ADU zoning page, 2026), and ORS 197A.425(1)(b)(B) bars Oregon cities from requiring it; converting a garage does not require replacement parking. Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
Not required. Chapter 33.205 has no owner-occupancy rule and ORS 197A.425 prohibits one. The only occupancy condition is voluntary: the 10-year covenant against short-term rental of any structure on the property that you sign to get SDCs waived. Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Portland is typically The city publishes no fixed ADU review time; plan review runs on DevHub with checksheet correction rounds, so allow for at least one. If a zoning standard is missed, the Adjustment Review alone takes about 8-10 weeks (city ADU zoning page, 2026). Plan check: Electronic single-PDF plan review on Development Hub PDX; paper plans by appointment only. New detached ADUs are reviewed under the Oregon Residential Specialty Code, conversions under the city's ADU Code Guide. A lot with 20% or steeper slope or in a landslide area needs a geotechnical report; a garage in a flood hazard area may not be convertible; trees with trunks over 12 in need protection measures. Pre-approved plans availability: Yes. The city offers 4 free pre-approved detached ADU plan sets (gable or shed roof, on a concrete slab or a wood-framed crawl space), adapted from the City of Eugene's plans. They are not suited to every lot: the shed-roof slab design exceeds the size allowed inside a side or rear setback, and the bathroom does not meet the visitability standard required when a lot has two ADUs. Truss packages can be a deferred submittal.
Average ADU rental income in Portland: 1-bedroom units rent for $1,400-$1,700/month, 2-bedroom units for $1,700-$2,200/month. Short-term rentals: Yes, with a permit: an ADU can be a Type A accessory short-term rental (up to 2 bedrooms, stays under 30 days) under Chapter 33.207, or Type B (3-5 bedrooms) via 33.815.040.B.1. Expected ROI: 6-9% gross rental yield on a $180,000-$280,000 detached build at $1,400-$2,200/mo (estimate before taxes, vacancy and financing).
The minimum lot size for an ADU in Portland is One ADU with a house: the lot only has to meet the base-zone minimum for a primary structure (33.110.202); no separate ADU minimum. One ADU with an attached house: Table 205-1 (R5 2,500 sq ft, R7 3,500, R10 5,000, R20 10,000, R2.5 1,500). Two ADUs, or one ADU with a duplex: Table 205-2 (R5 3,000 sq ft, R7 4,200, R10 6,000, R20 12,000, R2.5 1,500) plus frontage on a City-maintained street. This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Portland, a garage conversion typically costs $70,000-$160,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.
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