Portland has built one of the more permissive ADU frameworks in the Pacific Northwest, and understanding how that framework works in practice can save landlords and homeowners significant time and money. An accessory dwelling unit (ADU) is a secondary housing unit on the same lot as a primary residence; you may also hear them called granny flats, in-law suites, backyard cottages, or carriage houses. Property owners build them for rental income, multigenerational living, or simply to add long-term value to a lot.
Start here: confirming your property's eligibility
Before contacting a designer or attorney, verify that your lot allows an ADU. Portland's single-family residential zones (R1 through R20) generally permit ADUs by right under Title 33 of the Portland City Code, which means no discretionary land use hearing is required in most cases. Check your zoning designation at PortlandMaps.com. The site also flags overlays such as historic districts or flood zones that add requirements to the standard process.
Oregon's House Bill 2001 (2019) requires cities above 10,000 residents to allow ADUs in single-family zones by right. Portland was already ahead of that mandate, but the state law has pushed surrounding communities to loosen their own rules, gradually expanding housing supply across the metro area.
Types of ADUs Portland allows
Portland recognizes three main categories, each with slightly different standards.
- Detached ADU: A freestanding structure separate from the main house, such as a backyard cottage or converted garage.
- Attached ADU: An addition built onto the primary dwelling, sharing at least one wall.
- Junior ADU (JADU): A unit carved from existing interior space, typically under 500 square feet. JADUs require their own entrance, a bathroom, and basic kitchen facilities.
Portland allows one attached ADU and one detached ADU on a single-family lot in many zones, subject to coverage and setback limits. Verify your specific lot's allowances through PortlandMaps before committing to a design.
Size limits, setbacks, and other dimensional rules
The key dimensional standards under Title 33 include:
- Size: Detached ADUs cannot exceed 75% of the primary dwelling's floor area, with a cap of 800 square feet.
- Height: Most residential zones limit detached ADUs to 20 feet, though this varies by zone.
- Setbacks: The rear setback is typically 5 feet; side setbacks vary by zone. Check the Portland Bureau of Development Services (BDS) ADU guidelines for your specific zone.
- Lot coverage: The ADU counts toward the zone's total lot coverage maximum, usually 50%.
- Parking: No additional off-street parking spaces are required for an ADU anywhere in Portland.
- Owner-occupancy: Portland eliminated its owner-occupancy requirement in 2020. You don't have to live on the property to build or rent an ADU.
The permit process, step by step
The practical permit path runs through Portland BDS. Here's how the process works from first contact to final approval.
Step 1: pre-application conference
A pre-application conference with BDS staff costs roughly $200 and is optional but often worth it. Staff can flag site-specific issues before you've spent thousands on drawings. Schedule one through Portland BDS.
Step 2: prepare construction documents
You'll need site plans, floor plans, elevations, and energy compliance documentation. Most owners hire a licensed architect or designer at this stage. Design fees typically run $5,000 to $15,000 depending on project complexity. Incomplete drawings at submission are the leading cause of delays, so confirm energy compliance documents are included before submitting.
Step 3: submit permit applications
Submit through the Portland BDS online portal. A building permit is required at minimum. Separate permits for electrical, mechanical, and plumbing work are typically required as well. Submit all applications together if possible to avoid sequential review delays.
Step 4: plan review
Simple, complete submittals can clear plan review in four to eight weeks. Projects that trigger additional review, such as those affecting protected trees under Title 11 of the Urban Forestry Code or properties in historic or conservation overlays, can take four to six months. BDS posts current estimated review times on its website; check these before setting a construction schedule.
Step 5: construction and inspections
BDS inspectors visit at key construction milestones. Once all inspections pass, you receive a certificate of occupancy and the unit is legal to rent or occupy.
Common pitfalls that delay Portland ADU permits
A few recurring issues account for most project delays.
- Missing energy compliance documentation at submission
- Lot coverage calculations that overlook all existing impervious surfaces, including driveways and sheds
- Tree conflicts: Portland's Title 11 protects significant trees, and construction within root zones requires separate permits or mitigation
- Underestimating utility upgrade requirements, particularly sewer lateral capacity
- Historic district or conservation overlay requirements that trigger design review
The pre-application conference is the most reliable way to catch these issues early. Spending $200 upfront is far less costly than redesigning plans after a permit rejection.
What it costs to build a Portland ADU
New detached ADUs in Portland typically cost $200 to $350 per square foot to build. A 600-square-foot unit runs $120,000 to $210,000 all in. Garage conversions and basement conversions generally cost less, often $80,000 to $130,000 depending on condition and finishes. JADUs are the lowest-cost option, often $40,000 to $80,000, since no new foundation or major structural work is required.
Permit fees are calculated based on declared construction value. For a $150,000 project, expect roughly $3,000 to $5,000 in building permit fees, plus separate fees for electrical, plumbing, and mechanical work.
The most significant cost relief available is the System Development Charge (SDC) waiver. As of 2024, Portland waives SDCs for ADUs up to 800 square feet on owner-occupied properties, a savings of $15,000 to $25,000 or more. ADUs on non-owner-occupied properties or over 800 square feet may still owe SDCs. Confirm current waiver eligibility with BDS before budgeting.
Rental income and landlord considerations
ADU rents in inner Portland neighborhoods frequently range from $1,200 to $2,200 per month depending on size, location, and finishes. That income potential comes with regulatory responsibilities landlords should understand before renting.
Oregon's statewide rent stabilization law, enacted under House Bill 2001 (2019), caps annual rent increases and requires landlords to provide cause for no-fault terminations after 12 months of tenancy. Portland's Renter Relocation Assistance Ordinance adds local obligations around rent increases and lease terminations. These rules apply to ADU rentals just as they apply to other residential tenancies.
Protecting your rental investment with the right insurance policy is equally important. Coverage options vary widely, and what works for a primary residence policy often doesn't cover a rented ADU adequately. You can review what Oregon landlords typically need at Steadily's Oregon landlord insurance page.
HOA and neighborhood considerations
Portland city zoning allows ADUs in most residential zones, but a homeowners association can impose additional restrictions on design, aesthetics, or structure type. If your property is subject to CC&Rs, review those documents before finalizing plans. HOA restrictions operate independently of city zoning and BDS has no authority to override them.
Frequently asked questions about Portland ADU laws
Do I need to live on my Portland property to build an ADU?
No. Portland removed the owner-occupancy requirement in 2020. You can build and rent an ADU as a non-owner-occupant landlord, though the SDC waiver currently applies only to owner-occupied properties.
Can I build two ADUs on one Portland lot?
In many cases, yes. Portland allows one attached ADU and one detached ADU on a single-family lot, subject to lot coverage and setback limits. Verify your specific lot's allowances through PortlandMaps before designing.
How long does Portland ADU permit review take?
Simple projects with complete submittals typically move through plan review in four to eight weeks. Projects requiring tree permits, historic review, or land use review can take four to six months. Check BDS's current posted wait times before setting a construction schedule.
Can a detached garage be converted into an ADU?
Yes, and it's one of the most common ADU types in Portland. The converted structure must meet all building codes for habitable space, including insulation, egress, and electrical standards. A full building permit is required.
Does Portland require parking for an ADU?
No. Portland does not require additional off-street parking spaces for ADUs, which simplifies construction on urban lots where space is limited.
What happens if my ADU affects a protected tree?
Portland's Title 11 Urban Forestry Code protects significant trees. If construction affects a protected tree's root zone or canopy, you'll need a separate tree permit or must provide mitigation. This is one of the most common sources of unexpected delays and costs, so a pre-application conference is especially valuable on wooded lots.
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