Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Portland ADU cost →Building an ADU in Portland costs between $180,000-$280,000 for new construction, with per-square-foot costs averaging $250-$400. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $70,000-$160,000, while prefab/modular ADUs fall in between at $100,000-$240,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | 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 |
| Impact Fees | System development charges apply unless waived: Parks FY2025-26 $7,941 for a unit under 700 sq ft or $11,878 for 700-1,199 sq ft (non-Central City; indexed each July 1); Transportation FY2026-27 $3,421 (dwellings under 1,200 sq ft, including ADUs, pay half the single-family rate); Environmental Services sanitary SDC by plumbing-fixture count plus a stormwater SDC on new impervious area (see BES schedule); Water none unless the meter is upsized. The ADU SDC Waiver (Revenue Division application, 10-year covenant that no structure on the property will be a short-term rental, running from final inspection; breaking it costs 150% of the then-current SDCs) removes the Parks, Transportation and BES charges. The citywide temporary SDC exemption for new housing (permits issued Aug 15, 2025 - Sep 30, 2028) expressly excludes ADUs (PCC 17.14.070.J) |
| Site Prep & Foundation | $10,000 – $35,000 |
| Framing & Structure | $15,000 – $45,000 |
| Plumbing | $8,000 – $20,000 |
| Electrical | $5,000 – $15,000 |
| HVAC | $3,000 – $8,000 |
| Interior Finishes | $15,000 – $40,000 |
Quotes for the same ADU commonly vary 20–40% between builders. We pass your request to up to 5 local builders serving Portland, where we have them — free, no obligation.
Get Portland builder quotes →Permit fees in Portland are 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. The review timeline is 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), with 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. Impact fees are System development charges apply unless waived: Parks FY2025-26 $7,941 for a unit under 700 sq ft or $11,878 for 700-1,199 sq ft (non-Central City; indexed each July 1); Transportation FY2026-27 $3,421 (dwellings under 1,200 sq ft, including ADUs, pay half the single-family rate); Environmental Services sanitary SDC by plumbing-fixture count plus a stormwater SDC on new impervious area (see BES schedule); Water none unless the meter is upsized. The ADU SDC Waiver (Revenue Division application, 10-year covenant that no structure on the property will be a short-term rental, running from final inspection; breaking it costs 150% of the then-current SDCs) removes the Parks, Transportation and BES charges. The citywide temporary SDC exemption for new housing (permits issued Aug 15, 2025 - Sep 30, 2028) expressly excludes ADUs (PCC 17.14.070.J). Pre-approved plans: 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.
| 1-Bedroom Rent | $1,400-$1,700/month |
| 2-Bedroom Rent | $1,700-$2,200/month |
| Annual Rental Income (est.) | $18,600/year |
| Payback Period (est.) | 12.4 years |
| Short-Term Rental | 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. |
| Overall ROI Estimate | 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) |
A typical ADU in Portland generates approximately $18,600 per year in rental income based on average 1-bedroom rents. At an average construction cost of $230,000, the estimated payback period is 12.4 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Portland and varies by market (often less than build cost).
1. Garage conversions save 40-60% vs new construction since the shell already exists. Average cost in Portland: $70,000-$160,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $100,000-$240,000.
3. Pre-approved plans — available in Portland, which can save $3,000-$10,000 in design costs and 2-3 months in review time. See which cities offer pre-approved ADU plans.
4. State grants — California's CalHFA ADU grant (up to $40K) is currently paused; check calhfa.ca.gov/adu for status and your state for active programs.
5. Get multiple bids — ADU contractor pricing varies 20-40% for the same project. We recommend getting at least 3 quotes.
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