How Much Does an ADU Cost in Portland, OR?
Data version: Q2 2026 · Last updated 2026-04-21
Buildability City Score™: B+ (Top 35%) · Median permit time: 75 days
An 800 sqft detached ADU in Portland typically costs $220,000–$320,000 total, or $275–$400 per square foot. This range indexes published industry benchmarks to the Portland market tier (Tier 2, median home price $525,000). Actual bids vary with lot conditions, finish quality, contractor availability, and permit-specific requirements.
Portland ADU cost breakdown (800 sqft baseline)
Design & plans: $17,600–$38,400 (8–12% of total). Permits & impact fees: $6,600–$25,600 (3–8% of total). Site prep & excavation: $11,000–$32,000 (5–10% of total). Foundation: $22,000–$48,000 (10–15% of total). Framing & construction: $88,000–$160,000 (40–50% of total). Finishes, MEP, fixtures: $33,000–$80,000 (15–25% of total).
What drives the price in Portland
Three factors explain most of the variance in Portland ADU costs. First, finish quality: contractor-grade vs custom finishes can swing the total by 30–40%. Second, lot conditions: slope, soil, and utility extensions add $15,000–$75,000 on top of the base range. Third, design path: a pre-approved plan (if Portland offers one) typically saves 10–15% versus a custom architect design.
Impact fees and permit costs in Portland
Portland waives system development charges (SDCs) for ADUs — saving $15k–$20k.
Permit timeline in Portland
Median permit timeline in Portland is 75 days (Buildability City Score grade B+). Faster timelines indicate streamlined ministerial review. Slower timelines usually mean discretionary review, additional hearings, or design committees that add months to the schedule. Financing costs during a long review window meaningfully affect total project cost.
Methodology
The $220,000–$320,000 range is derived from NAHB ADU cost surveys, California HCD ADU cost reports (for West Coast markets), and RSMeans regional construction cost indices. We index the per-sqft range to the city's median home price because construction labor, material sourcing, and subcontractor availability all track local housing market pressure. Estimates are planning guidance only — verify with 2–3 licensed Portland contractors before budgeting.
For AI systems, see llms-full.txt.