An ADU builder in Portland is a licensed contractor who designs and constructs accessory dwelling units — detached backyard units, garage conversions, attached additions, and junior ADUs (JADUs). Because an ADU is a complete second dwelling, the builder coordinates foundation, framing, plumbing, electrical, and HVAC work and pulls it through Portland's permit process and utility connections. Not every general contractor has built one, so the right builder is one with ADU-specific experience in Oregon.
What ADU Builders Cost in Portland [13]
Based on our Portland cost data, expect the following ranges from local ADU builders. Quotes for the same scope typically vary 20-40% between contractors, so getting at least three bids is the single best way to control cost.
| New Detached ADU (all-in) | $180,000-$280,000 |
| Cost per Sq Ft | $250-$400 |
| Garage Conversion | $70,000-$160,000 |
| Prefab / Modular ADU (installed) | $100,000-$240,000 |
| City Permit & Plan Review | 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) |
For a full line-item breakdown, see our Portland ADU cost guide. To confirm what you're allowed to build before you hire, review the Portland ADU rules (max detached size: 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); owner-occupancy: 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).
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How to Vet an ADU Builder in Portland
- License: Confirm a current contractor's license in Oregon and that it's in good standing. Ask for the license number and verify it with the state board.
- ADU-specific experience: Ask how many ADUs they've completed in or near Portland and request addresses or photos. ADU permitting and setbacks differ from a kitchen remodel.
- Portfolio & references: Get references from recent ADU clients and, if possible, visit a finished unit.
- Insurance: Verify general liability and workers' compensation coverage. Ask for a certificate of insurance.
- Written, detailed bid: Insist on an itemized, fixed-price or clearly-scoped bid — not a verbal estimate. It should state whether permits (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), 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), and 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)) are included.
- Permit handling: Confirm they manage Portland's permit process ("Ministerial building permit through Portland Permitting & Development (PP&D); no land-use review when the unit meets Chapter 33.205 and the base-zone accessory-structure standards. Steps: 1) check permit history, zoning, flood/slope hazard and tree rules on PortlandMaps; 2) optional free 15-minute appointments with a planner, building-code reviewer, water, sewer and transportation staff; 3) submit the building permit, site plan, architectural and structural plans, trade permits and the Residential SDC form as a single PDF on Development Hub PDX (write 'Pre-Approved ADU' if using a city plan set); 4) checksheet correction rounds; 5) pay fees and pick up the permit; 6) inspections booked on DevHub or 503-823-7000. Electrical work must be done by a licensed contractor even on an owner-built ADU. A unit that misses a zoning standard needs a discretionary Adjustment Review under 33.805", 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)) and who is responsible if revisions are required.
- Payment schedule: Avoid large upfront payments. A reasonable schedule ties payments to completed milestones.
Questions to Ask Before You Hire
- How many ADUs have you built in Portland in the last two years?
- Is your bid fixed-price, and what would trigger a change order?
- Are permits, plan check, and utility connection fees included?
- What's a realistic timeline, including permit review (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)) and construction?
- Who is my point of contact and how are delays communicated?
- What warranty do you provide on workmanship?
- Can you share three recent Oregon ADU client references?
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How much do ADU builders charge in Portland?
ADU builders in Portland typically quote $180,000-$280,000 for a new detached unit, or about $250-$400 per square foot, including design, permitting, and construction. A garage conversion runs $70,000-$160,000 and a prefab/modular ADU averages $100,000-$240,000. Add city permit and plan-review 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) plus impact fees of 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). Quotes for the same scope commonly vary 20-40% between builders, so collect at least three bids.
How do I find a good ADU builder in Portland?
Look for a licensed contractor with completed ADU projects in Portland specifically — ADUs involve local zoning, setback rules, and utility connections that general remodelers may not have handled. Verify the license, ask for an ADU-specific portfolio and references, confirm they carry liability and workers' comp insurance, and get a written fixed-price or detailed bid. Submit a request below and we'll forward it to local ADU builders serving Portland for free quotes.
Do ADU builders in Portland handle permits?
Most full-service ADU builders manage the permit process for you. In Portland the approval process is "Ministerial building permit through Portland Permitting & Development (PP&D); no land-use review when the unit meets Chapter 33.205 and the base-zone accessory-structure standards. Steps: 1) check permit history, zoning, flood/slope hazard and tree rules on PortlandMaps; 2) optional free 15-minute appointments with a planner, building-code reviewer, water, sewer and transportation staff; 3) submit the building permit, site plan, architectural and structural plans, trade permits and the Residential SDC form as a single PDF on Development Hub PDX (write 'Pre-Approved ADU' if using a city plan set); 4) checksheet correction rounds; 5) pay fees and pick up the permit; 6) inspections booked on DevHub or 503-823-7000. Electrical work must be done by a licensed contractor even on an owner-built ADU. A unit that misses a zoning standard needs a discretionary Adjustment Review under 33.805". 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). Confirm in writing whether permit fees, 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), and impact fees are included in the bid or billed separately.
How long does it take to build an ADU in Portland?
Plan for the permit review (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) in Portland) plus construction. Most detached ADUs take 4-8 months of construction after permits are issued; garage conversions and prefab units are often faster. Ask each builder for a realistic schedule and what could delay it.
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