The short answer: The biggest Portland ADU cost from the City is usually not the building permit but the system development charges (SDCs). For a detached ADU under 700 sq ft outside the Central City, the Parks SDC ($8,041) and the Transportation SDC ($3,421) add up to $11,462 for fiscal year 2026-27, before sewer and stormwater charges. The City lets you waive SDCs by signing a covenant that bars short-term rental use for 10 years. Breaking it costs 150% of the then-current SDCs. We found no current neutral dataset on what Portland ADUs cost to build, so this guide covers what the City publishes and leaves construction pricing to written bids.
Last verified: October 5, 2026 ยท Written by the ADU Scope editorial team
Attention: SDC rates change every July 1, and the amounts below are for fiscal year 2026-27 as published on portland.gov. Confirm the current figure with Portland Permitting & Development before you budget. We could not confirm from the City’s pages which SDC types the waiver covers beyond Parks and Transportation, or the Water Bureau’s charges, which this guide does not cover.
Portland ADU Cost: System Development Charges, FY 2026-27
In short, SDCs are one-time charges for the burden a new dwelling places on public systems. Specifically, Portland lists adding an ADU as an SDC trigger, and the Parks bureau states that ADUs are subject to Parks SDCs under the same calculations as other residential development. However, the City’s temporary SDC exemption for new housing (building permits issued August 15, 2025 through September 30, 2028) does not apply: it excludes ADUs, which have a separate waiver program.
| Charge | Unit size | Amount (7/1/2026 to 6/30/2027) |
|---|---|---|
| Parks SDC, outside the Central City | Under 700 sq ft | $8,041 |
| Parks SDC, outside the Central City | 700 to 1,199 sq ft | $12,028 |
| Parks SDC, Central City | Under 700 sq ft | $6,359 |
| Parks SDC, Central City | 700 to 1,199 sq ft | $9,511 |
| Transportation SDC (ADUs pay the single-family rate) | Under 1,200 sq ft | $3,421 |
| Transportation SDC (single-family rate) | 1,200 sq ft or larger | $6,841 |
Next, combining the Parks and Transportation lines gives the amounts most owners focus on. This is our addition of the City’s figures:
| Unit size and location | Parks + Transportation |
|---|---|
| Under 700 sq ft, outside the Central City | $8,041 + $3,421 = $11,462 |
| 700 to 1,199 sq ft, outside the Central City | $12,028 + $3,421 = $15,449 |
| Under 700 sq ft, Central City | $6,359 + $3,421 = $9,780 |
| 700 to 1,199 sq ft, Central City | $9,511 + $3,421 = $12,932 |
Sewer and stormwater
Meanwhile, Environmental Services publishes its residential rates for fiscal year 2026-27 as follows: the sanitary SDC is 60% of the Tier 1 rate, which equals $373.80 per drainage fixture unit, and the stormwater SDC is $580 per 1,000 sq ft of billable area. There is no flat per-ADU amount, because the sanitary charge depends on the number of fixture units in the design. Therefore, ask the City for an estimate based on your plans.
Key fact: An SDC of about $11,000 to $15,000 is a real part of the budget. Our sample budgets show base project costs of $100,000 to $400,000, so the Parks and Transportation SDCs alone can be a noticeable share of a smaller project.
Cutting Portland ADU Cost With the 10-Year SDC Waiver
First, Portland’s ADU SDC waiver is a separate program from the temporary exemption. According to the City’s page:
- It covers new ADUs that owners occupy or rent month-to-month or longer. It does not cover short-term rentals or accessory short-term rentals.
- You sign a binding agreement promising that you will not rent the ADU or the house as a short-term rental for 10 years. It also runs with the property and binds later owners.
- In addition, the 10 years start on the day of final inspection approval.
- Finally, breaking the covenant requires paying 150% of the current SDC fees, which is also the cost to revoke it.
Which SDCs the waiver covers
Moreover, the Parks bureau and the Transportation bureau each confirm on their own pages that a signed, notarized 10-year covenant waives their SDC. The waiver page itself does not list the SDC types, so ask the City whether the waiver also covers the Environmental Services and Water charges.
| Choice | Cost today (example: under 700 sq ft, outside Central City) | Constraint |
|---|---|---|
| Pay the SDCs | About $11,462 for Parks and Transportation, plus sewer and stormwater | None on short-term rental beyond zoning rules |
| Sign the waiver covenant | $0 for the waived SDCs | No short-term rental for 10 years. At today’s rates, breaking it would cost 150% of $11,462, about $17,193 for those two charges alone |
Paying the SDCs or signing the covenant
For owners who plan long-term rentals or family use, the waiver is attractive. By contrast, for anyone planning Airbnb-style income, the covenant defeats the purpose. Decide your rental strategy before you apply, and note that the penalty follows the rates in force when you break the covenant, not today’s rates.
Tip: Therefore, read the covenant text itself before signing and ask an attorney how a 10-year restriction that binds future owners could affect resale. Also, the City recommends applying early in the permitting process.
Zoning Rules That Shape Portland ADU Cost
- Size: an ADU can be up to 75% of the main structure’s living area or 800 sq ft, whichever is smaller. The cap does not apply to basement ADUs in primary structures at least five years old. A small house therefore limits the size of a new detached ADU.
- Number: one ADU on lots with a house, attached house or manufactured home in all residential zones. Some zones permit two ADUs on qualifying lots.
- Parking: the City states that an ADU needs no extra on-site parking, which avoids a common hidden cost.
- Height and placement: the City caps detached ADUs at 20 feet in height, or 15 feet within the setback, and they must sit at least 40 feet from the front lot line or behind the rear wall of the main structure.
- Adjustment Review: if your design does not meet the standards, you need an Adjustment Review. It is discretionary, takes about 8 to 10 weeks and does not guarantee approval.
Also, our guides to Oregon ADU rules and ADU setback requirements cover the legal framework.
Portland ADU Cost: Permit Fees and Review
Portland bases its building permit fees on project valuation under the fee schedule that took effect in July 2026, and it charges no flat ADU fee. For new construction and additions, the City uses the greater of the applicant’s stated value or the figure from the ICC Building Valuation Data Table multiplied by square footage. In addition, plan review for the original submittal is 65% of the building permit fee. Likewise, a pre-application consultation for a one- or two-family dwelling or ADU costs $305 for a project valued up to $100,000 and $640 above that. However, we did not find an official review time for ADU building permits, other than the Adjustment Review timeline above, so ask the City for a current estimate.
Portland ADU Cost to Build: What We Found
We did not find a current neutral source on Portland ADU construction costs from the City, Metro or the state, and we do not quote builder ranges for Portland because no primary source backs them. In fact, the only government-hosted study we found is a 2014 survey of 81 Portland ADU developers by Portland State University researchers, which Oregon’s Department of Environmental Quality hosts. Overall, it reported a median cost of $65,000 ($108 per sq ft) with a median of $45,500 for attached and $90,000 for detached units. Developers reported the costs themselves, and nobody adjusted them for inflation, so they are far too old to budget from.
For a method that works anywhere, see our guide to what an ADU costs in California: separate the unit type, ask for prices at two sizes and collect three written bids that cover the same items. Our guide to hidden costs and utility hookups lists what bids often leave out.
Steps to Estimate Your Portland ADU Cost
- First, decide between a conversion and a new detached unit.
- Next, check the size cap against your main house.
- Then ask the City for a fee estimate that separates permits from SDCs.
- Also decide whether you will sign the short-term-rental covenant.
- Afterward, get three line-item construction bids that state what they include.
- Finally, add time for at least one correction round and, if needed, an Adjustment Review.
Frequently Asked Questions
What SDCs apply to a Portland ADU?
Parks, Transportation, Environmental Services (sanitary and stormwater) and Water. The Parks and Transportation amounts for FY 2026-27 are in the tables above.
Can I avoid SDCs?
Yes, through the City’s ADU SDC waiver. In exchange, you sign a 10-year covenant against short-term rental use.
What happens if I break the covenant?
In that case, the City states that you must pay 150% of the current SDC fees.
Does the temporary SDC exemption apply to ADUs?
No. The City’s temporary exemption for new housing excludes ADUs, because they have their own waiver program.
Do I need extra parking?
No. The City states that an ADU needs no extra on-site parking.
Next Steps
- Oregon ADU Rules: Statewide Requirements and Portland Specifics
- ADU Setback Requirements Explained
- ADU Impact Fees: When You Pay Them and How to Avoid Them
- Seattle ADU Fees: Permit, Sewer Capacity and Utility Charges
General information, not financial or legal advice. Rates, fees and waiver terms change; confirm with the City of Portland.
Sources: City of Portland: ADU SDC waiver ยท Portland Parks & Recreation: FY 2026-27 SDC schedule ยท Portland Bureau of Transportation: Transportation SDC ยท Environmental Services: rates and charges ยท City of Portland: temporary SDC exemption ยท City of Portland: ADU zoning ยท City of Portland: building permit fee schedule (July 2026) ยท Brown and Palmeri: Accessory dwelling units in Portland, Oregon (2014)