Skip to main content
2026 Cost Guide · Updated September 2026

ADU Cost in Oregon — Portland, Eugene, Bend & Statewide

Real ADU pricing across Portland, Eugene, and Oregon's other major markets, driven by wet-climate construction realities, the Oregon Residential Specialty Code, and a Portland labor market with its own dynamics.

$140K–$380K Detached ADU range
$65K–$140K Garage conversion (lowest cost)
Since 2017 Nation's oldest statewide ADU mandate (ORS 197A.425)
SDCs waived Portland waives fees under 800 sqft
Oregon ADU front elevation, Craftsman-modern hybrid style
Oregon ADU kitchen interior Oregon ADU living room interior
Aerial view of an Oregon property with backyard ADU
Oregon ADU bedroom interior Oregon ADU bathroom interior Oregon ADU outdoor living and patio space
Homeowners reviewing ADU permit documents in Oregon
Start Here — The Legal Framework

One of the oldest ADU mandates in the country.

Oregon's statewide ADU requirement dates to 2017's SB 1051, now codified as ORS 197A.425 — two years before the state's better-known "middle housing" law (HB 2001, 2019) legalized duplexes through fourplexes. The two laws are often confused, but they're different: HB 2001 is about multi-unit buildings; ORS 197A.425 is specifically the ADU mandate. It requires every city with more than 2,500 residents, and every county with more than 15,000 residents, to allow at least one ADU per detached single-family home inside its urban growth boundary. Covered jurisdictions cannot require owner-occupancy of either unit, cannot mandate extra off-street parking, but may impose "reasonable" siting and design rules — a 2023 court ruling confirmed that means where the ADU sits on the lot, not whether an area allows ADUs at all.

Portland goes further than the state requires. The city waives System Development Charges entirely for ADUs under roughly 800 sq ft, provided the owner signs a covenant not to use the unit as a short-term rental for 10 years — plus four pre-approved detached ADU designs at no design cost. Eugene and Bend, both inside the statewide mandate, set their own local siting and design rules on top of it.

📄
Building Permit — Portland
$4,000 – $10,000
Based on project valuation.
🏗️
System Development Charges (SDCs)
$0 – $15,000
Waived in Portland for ADUs under ~800 sqft with a 10-year no-STR covenant.
💧
Utility Connection Fee
$3,000 – $12,000
Sewer, water, and electrical connections.
📋
Plan Check Fee
$1,500 – $4,000
Structural/architectural review.
🧾
Total Typical Range
$18,000 – $40,000
Portland; lower in smaller Oregon cities.
Verified September 16, 2026 · Effective framework
ORS 197A.425 (originally SB 1051, 2017)

Cities over 2,500 residents and counties over 15,000, within urban growth boundaries, must allow at least one ADU per single-family lot.

Legal classificationEffective framework
Governing frameworkORS 197A.425 (SB 1051, 2017)
Not to be confused withHB 2001 (2019) — middle housing
Representative permit fees$4,000 – $10,000
Local verificationRequired

Source: Oregon DLCD — Housing Statutes →

Verify the property before design

These are planning benchmarks, not a permit quote, eligibility ruling, or legal opinion. Confirm zoning, building, utility, site, private-covenant, fee, and timing requirements with the current local authorities. See the 51-jurisdiction law directory and national permit guide.

ADU Types

Which type fits your property?

01 / Most Common
Detached ADU
$140K – $380K

A 600 sqft detached ADU in Portland typically runs $200,000–$300,000 including permits — and Portland's SDC waiver for units under 800 sqft cuts upfront cost significantly versus other Oregon cities.

Detached ADU Guide →
02 / Most Affordable
Garage Conversion
$65K – $140K

Oregon's older housing stock — especially Portland's bungalows and craftsman homes — frequently has detached garages that are ideal ADU candidates, often with alley access that simplifies permitting.

Garage Conversion Guide →
03 / Fastest Timeline
Modular / Prefab
$180K – $280K

Several prefab ADU providers serve the Portland market. Prefab ADUs typically reach occupancy 4–6 months faster than site-built construction — a meaningful edge given Oregon's wet-season construction delays.

Prefab ADU Overview →
04 / Shared Utilities
Attached ADU
$120K – $320K

An addition sharing a wall with the main house. Shared utility connections reduce hookup costs versus a fully detached unit, and still qualifies for Portland's SDC waiver under 800 sqft.

Attached ADU Guide →
05 / Common in Portland
Basement Conversion
$80K – $160K

Portland's residential neighborhoods have a high share of homes with full basements, making this a cost-effective option. Main cost drivers are egress windows, a bathroom addition, and separate utility metering.

Basement ADU Guide →
Cost by Region

Every Oregon market is different.

Portland Metro
Portland · Bureau of Development Services
$220K–$380K
$290–$380 per sq ft
Highest cost
Bend / Central Oregon
Deschutes County
$210K–$360K*
$280–$360 per sq ft
Very high
Eugene / Springfield
Lane County
$180K–$290K*
$240–$310 per sq ft
Moderate
Salem Metro
Marion County
$165K–$270K*
$220–$290 per sq ft
Moderate
Medford / Ashland
Jackson County
$175K–$280K*
$230–$300 per sq ft
Moderate
Corvallis / Albany
Benton · Linn County
$165K–$260K*
$220–$280 per sq ft
Standard

*Total-cost ranges outside Portland are derived from regional $/sq ft data at a representative ~800 sq ft build; verify against local bids before publishing final figures.

Cost Factors

Why Oregon ADUs cost what they cost.

🌧️
Wet-Climate Construction
Oregon's wet winters (especially west of the Cascades) can slow exterior work — projects starting construction in fall commonly see weather-driven delays, and engineered drainage and quality roofing add real cost.
Adds timeline risk in fall/winter starts
📐
Oregon Residential Specialty Code
One of the stricter residential energy codes in the country. ADUs must meet current insulation, window performance, and mechanical efficiency standards — adding upfront cost but reducing long-term tenant utility bills.
Adds design & material cost statewide
👷
Portland Labor Market
Portland's construction labor costs run above the national average, pushing Portland metro toward the top of Oregon's cost range. Smaller cities like Corvallis and Salem see meaningfully lower labor costs.
Portland premium vs. rest of state
⚖️
Current ADU Legal Framework
Covered cities and urban county areas must allow ADUs under state housing law; local siting, building, and permit rules still apply.
Effective framework · ORS 197A.425
At a Glance

Oregon ADU costs — by type.

Detached ADU
$140K – $380K
$220–$380 per sq ft · Portland & Bend skew highest
🏡
Attached ADU
$120K – $320K
Shared utility hookups reduce connection cost
🔗
Garage Conversion
$65K – $140K
Portland's bungalow/craftsman stock is conversion-ready
🚗
Basement Conversion
$80K – $160K
Portland has a high share of homes with full basements
⬇️
Modular / Prefab
$180K – $280K
Reaches occupancy 4–6 months faster than site-built
📦
💡

Effective framework: ORS 197A.425. Covered cities and urban county areas must allow ADUs under state housing law; local siting, building, and permit rules still apply. Permit fees and review timing remain planning estimates until confirmed for the specific property.

Calculate My ROI →
Return on Investment

Oregon ROI planning inputs.

$1,100–$1,550
Adopted statewide 1-bedroom rent range
15%
National property-value planning input
10%–20%
Property-value uncertainty range
30%
Operating-expense planning reserve
Rent source
HUD FY2026 revised
One-bedroom FMR market basket
Exact HUD mappings
ROI-CM-1.4
Home-value source
Statewide Zillow ZHVI
June 30, 2026
One statewide input
Not a valuation
Payback period
Calculated live
Budget, ADU type, size and rent
Open calculator →
No static statewide promise
Full methodology
Transparent sources
HUD, Census PUMS, Zillow and FHFA
Review methodology →
Planning estimate, not a valuation
Save Money

7 ways to cut your
Oregon ADU cost now.

ORS 197A.425 already guarantees your right to build in most Oregon cities. These moves target the design fees, timeline, and code costs that remain within your control.

Calculate My ADU ROI →
Compact detached ADU exterior with Craftsman-modern styling
🏡
Compact Detached ADU
Oregon — statewide range
Property-Value Planning Input
15%
1
Keep your ADU under 800 sqft in Portland
Portland waives System Development Charges entirely for ADUs under 800 sqft — a $15,000–$30,000 saving. Sizing your design to stay under that threshold is one of the single highest-leverage decisions you can make.
Saves $15,000–$30,000 in Portland
2
Convert a garage if your home has one
Oregon's older bungalow and craftsman housing stock — especially in Portland — frequently has detached garages with alley access already in place, which simplifies both permitting and utility connections.
Saves 40–55% vs. new construction
3
Start construction in spring, not fall
Oregon's wet winters can slow exterior work significantly. Projects that begin site work in spring get a full dry construction season before the fall rains return, avoiding costly weather-driven delays.
Avoids weather-driven schedule delays
4
Use an ADU-specialized design firm in Portland
Portland has several design firms that focus exclusively on ADUs and already know the Bureau of Development Services' review process, which can meaningfully compress the 60–90 day permit timeline.
Faster permit review, fewer revision cycles
5
Consider a basement conversion if you have one
Portland's high share of full-basement homes makes this a genuinely cost-effective option at $80,000–$160,000 — often cheaper than a new detached structure, with the main costs being egress windows and a bathroom addition.
Often 20–40% less than new detached construction
6
Budget for Oregon's energy code from the start
Oregon's Residential Specialty Code has stricter insulation, window, and mechanical efficiency requirements than many states. Pricing this into your initial budget avoids surprise costs mid-project, and pays back through lower long-term utility bills.
Avoids mid-project change orders
7
Verify your contractor's CCB license before hiring
Confirm any contractor's license at oregon.gov/ccb, and request references from at least three completed ADU projects. Portland's ADU contractor ecosystem is well developed — there's no reason to skip this step.
Prevents costly contractor disputes
Frequently Asked Questions

Oregon ADU answers.

Can I build an ADU anywhere in Oregon?
State law — ORS 197A.425, originally passed as SB 1051 in 2017 — requires every Oregon city with more than 2,500 residents and every county with more than 15,000 residents to allow at least one ADU on every lot zoned for single-family housing, inside the urban growth boundary. This is a different, older law than the more famous HB 2001 (2019) "middle housing" statute, which covers duplexes through fourplexes. Cities cannot require owner-occupancy or additional off-street parking, though reasonable siting and design rules are allowed — always verify current specifics with your local planning department.
Is Oregon's ADU law the same as HB 2001?
No, and this is a common mix-up. HB 2001 (2019) is Oregon's middle-housing law, legalizing duplexes through fourplexes on lots that used to allow only single-family homes. The ADU mandate is a separate, older law, ORS 197A.425 (originally SB 1051, 2017), which specifically requires covered cities and counties to allow at least one accessory dwelling unit per single-family lot.
Does Portland waive ADU fees?
Yes. Portland waives System Development Charges (SDCs) for ADUs under 800 sqft, which can save $15,000–$30,000 compared to other jurisdictions. This waiver applies to both detached and attached ADUs and is currently in effect through at least 2027.
What is Oregon's energy code requirement for ADUs?
Oregon has one of the stricter residential energy codes in the country (Oregon Residential Specialty Code). ADUs must meet current energy efficiency standards including insulation, window performance, and mechanical system efficiency. This adds cost compared to older construction but reduces long-term utility expenses for tenants.
Can I rent my Oregon ADU short-term?
Portland requires a short-term rental permit and limits short-term rentals to owner-occupied primary residences — meaning you generally cannot rent a detached ADU on Airbnb in Portland unless you live in the main house. Eugene and other Oregon cities have varying short-term rental rules; check local ordinances before planning.
How do I find an ADU contractor in Oregon?
Oregon requires all contractors to be licensed with the Construction Contractors Board (CCB). Verify any contractor's CCB license at oregon.gov/ccb before hiring. Portland has a well-developed ADU contractor ecosystem — request references from at least three completed ADU projects and get a minimum of three bids before committing.
What is the cheapest ADU to build in Oregon?
Garage conversions are the least expensive option, typically $65,000–$140,000. Oregon's older housing stock, especially Portland's bungalows and craftsman homes, frequently has detached garages that are strong conversion candidates, often with alley access already in place.
What is the ROI on an ADU in Oregon?
The adopted Oregon one-bedroom planning range is $1,100–$1,550 per month, derived from the HUD FY2026 revised FMR market basket under ROI-CM-1.4. Payback is calculated from the homeowner's budget, ADU type, size, rent range, and a 30% operating-expense reserve. Property value uses a 15% national planning input with a 10%–20% uncertainty range; it is not a valuation.
Oregon ADU exterior at twilight, warm interior light glowing
Imagine coming home to your own Oregon ADU.

Ready to find out what your ADU will actually cost?

Start with the ROI calculator. Free, no signup, no contractor pitch. Just the data.

Calculate My ROI → All 50 State Guides
Planning Disclaimer: Cost, fee, and timeline ranges are approximations for education and early planning; actual requirements and costs vary with the property, local authority, utilities, site conditions, design, and contractor. The Oregon legal classification and framework shown here were verified on September 17, 2026, but they do not determine parcel eligibility and are not legal advice. Confirm current zoning, building, utility, private-covenant, fee, and timing requirements directly with the applicable authorities before design or construction. Obtain at least three contractor bids before committing to a project budget. Last updated September 2026.