Permit Required? Required
Typical Fee Range $2,500–$7,500 SDC waivers available for units restricted from Short-Term Rental use (2026 rules).
Fee Method Valuation-based
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What's Required in Portland

  • ADUs are allowed on most residential lots citywide (Attached or Detached).
  • Maximum size of 800 sq ft or 75% of the primary dwelling (whichever is less).
  • Must have independent kitchen, bathroom, and a separate entrance.
  • System Development Charge (SDC) waivers apply if unit is not used as an AIRBNB for 10 years.
  • Must maintain 5-foot setbacks from side and rear property lines.
  • No additional off-street parking is required for ADU units in Portland.

How Much Does an ADU Permit Cost in Portland?

Budget $2,500–$7,500 for the Portland permit itself (valuation-based), issued by the Portland Permitting & Development — but treat that as the entry fee, not the total. ADUs are full dwelling units, so the permit stack usually includes building, electrical, plumbing, and mechanical trade permits, plus plan review. One break on record here: SDC waivers available for units restricted from Short-Term Rental use (2026 rules). Get an itemized fee estimate from the department before finalizing your budget; the spread between a simple conversion and a new detached build is wide.

ADU Size Limits and Zoning Rules in Portland

Before drawing plans, check the two gates that sink most ADU projects: size and zoning. On record here, the size ceiling is 800 square feet or 75% of the primary dwelling (whichever is less). Other recorded conditions: no additional off-street parking is required for ADU units in Portland. Setbacks, height limits, and utility connections layer on top of those rules. The Portland Permitting & Development can confirm what your specific lot allows — worth doing before you pay for architectural drawings rather than after.

How to Get a ADU Permit in Portland

1

Step 1: Check SDC Waiver Eligibility

Verify if you can bypass $10k+ in impact fees by agreeing to rental restrictions.

2

Step 2: Professional Plans

Hire an architect to prepare detailed structural, site, and MEP plans.

3

Step 3: DevHub Submission

Submit 'Residential New Construction' application via Development Hub PDX.

4

Step 4: Fee Payment

Pay the permit and plan check fees ($2,500+ typical without waivers).

5

Step 5: Full Inspection Series

Complete all sequence inspections (Foundation to Final).

Frequently Asked Questions

Yes, detached accessory dwellings are allowed citywide on qualifying residential lots.
City fees typically range from $2,500 to $7,500 depending on SDC waiver status.
It is a program where the city waives 'System Development Charges' in exchange for long-term housing use.
On record, the ceiling is 800 square feet — with the exact limit depending on ADU type and lot. Confirm your configuration with the Portland Permitting & Development.
SDC waivers available for units restricted from Short-Term Rental use (2026 rules).