What happens if you skip the permit (and you needed one)
- Stop-work orders and fines up to $5,000, plus lien on property if unpermitted ADU is discovered during title search or neighbor complaint.
- Insurance claim denial: your homeowner policy will not cover liability, fire, or theft in an unpermitted dwelling unit, and mortgage lender will demand removal or refinance will be blocked.
- Resale disclosure hit: Oregon requires disclosure of all structures and unpermitted ADU voids ability to sell without remediation (typically $8,000–$15,000 to bring up to code or demolish).
- Forced removal order: City of Portland has enforced demolition of unpermitted ADUs costing $10,000–$30,000 in labor and disposal, with homeowner liable.
Portland ADU permits — the key details
Oregon Revised Statute 197.312 (2019) mandates that all cities allow ADUs on single-family residential lots, and Portland implemented this by deleting local parking, owner-occupancy, and setback restrictions that had blocked ADUs before 2019. The result: Portland Building Department cannot deny a permit for an ADU on the basis of zoning alone. What CAN still trigger a denial: inadequate lot size (minimum 2,500 sq ft for a detached ADU under Portland Code 33.205.040), setback violations (detached ADU must maintain 5 feet from side/rear property lines, versus 10 feet for some garage conversions), or failure to provide separate utilities (water, sewer, electric metered separately from the primary house, or approved sub-metering). The 2019 Oregon law also deleted the owner-occupancy requirement, so you can rent out the ADU without living in the primary house — a major change from older state law. Portland's online system (PortlandMaps + Bureau of Development Services, or BDS) accepts applications 24/7, and you can track plan review status in real time. One local quirk: Portland's system tracks 'Type A' and 'Type B' ADU definitions (Type A = detached new construction or garage conversion up to 800 sq ft; Type B = junior ADU carved out of main house up to 500 sq ft). Type A requires full building permit and plan review; Type B is streamlined but still mandatory.
The frost-depth and soil variance across Portland's geography matters more than most cities. In the Willamette Valley portions (west side, downtown to SW Hills), frost depth is 12 inches, which simplifies foundation design and cost — frost walls can be shallower, and you'll avoid the $2,000–$3,000 pile foundation premium that east-of-Cascades lots often trigger. Volcanic and alluvial soils in the valley tend to drain reasonably well, but the city's floodplain overlay (mapped in PortlandMaps) can require fill elevation or pile support if your lot is in the '100-year' or '500-year' zones. In contrast, parts of outer east Portland and SE, where expansive clay soils are common, geotechnical reports (soils test, ~$500–$800) are often required before foundation design, adding 1-2 weeks to the plan-review timeline. Always check your address in PortlandMaps before design: if you're in a floodplain, riparian overlay, or hillside district (SW Hills, Forest Park fringes), your ADU footprint, height, and parking may have additional constraints that don't apply to flat, valley-floor lots. The city's preapproved ADU plan library (available on BDS website) has three standard templates that bypass detailed geotechnical review if your lot qualifies — this can save $800–$1,200 in plan-prep costs and compress timeline to 30 days.
Parking is the headline relief under state law, but Portland's implementation has a twist. Oregon law eliminated the parking mandate for ADUs, meaning you do NOT need to provide off-street parking for the ADU itself. However, if your primary driveway/parking situation is substandard to begin with (only one space for a two-bedroom main house + one-bedroom ADU), the city's plan reviewer may flag it as a code-enforcement issue at final inspection — not a permit-blocking issue, but a condition you'll want to clarify upfront. In practice, most Portland ADU applicants with driveways pass through without a parking negotiation. Utility metering is mandatory and non-negotiable: you must show separate service panels, water meters, and sewer connections (or approved sub-meters for water and sewer if the lot's utility lines don't support two full services). This is the #1 reason for plan-review 'requests for information' (RFIs) — applicants submit sketches without utility details, BDS asks for clarification, and 2-4 weeks vanish. If your lot is uphill from the main sewer (common in SW Portland), you may need a sump pump or ejector pump ($1,500–$3,000), which adds complexity and timeline. Electrical sub-metering is standard practice and adds minimal cost ($200–$500 extra for the sub-panel), but you must hire a licensed electrician to design and install — owner-builder is allowed for the ADU shell construction, but not for electrical service upgrades.
Inspections for ADUs in Portland follow the full building sequence: foundation (before pour or after piers set), framing (before sheathing), rough MEP (mechanical, electrical, plumbing — before walls close), insulation, drywall, and final. In addition to the building inspector, you'll need a separate utility inspector (for water/sewer/electric mains) and a planning sign-off (to confirm setbacks, height, lot coverage). This is 5-7 scheduled inspections over 2-4 months of construction, which is normal but worth budgeting for — if the inspector finds code violations, re-inspection fees can add $300–$600 per round. Portland's inspection scheduling is online (you book via BDS portal), and turnaround is typically 2-3 business days. One local detail: if your main house is in a historic district (Laurelhurst, Nob Hill, Mt. Tabor, etc.), the ADU may trigger a Historic Design Review step before building permit is issued — add 4-6 weeks and $800–$1,200 in design modification and review fees. Check PortlandMaps 'Historic Landmarks' layer before spending on design.
Timeline and cost summary for Portland ADUs: with a standard detached ADU (800 sq ft, separate utilities shown, no historic or floodplain overlay), plan review takes 8-12 weeks, and total permitting cost (plan review, permit, system development charges for new sewer/water connection) runs $4,000–$8,000. If you use a preapproved plan, timeline compresses to 30 days and cost drops to $2,500–$4,000. If your lot is in a floodplain, historic district, or requires a geotechnical report (expansive soil), add 4-8 weeks and $1,500–$3,000. Construction costs are separate and typically run $120–$180 per square foot for a detached ADU (labor + materials), so an 800 sq ft unit costs $96,000–$144,000 to build in Portland's labor market (as of 2024). Owner-builder is allowed if you own the lot and occupy the primary residence, which can save 10-20% on labor ($10,000–$25,000 depending on scope), but you'll still need to hire licensed trades for electrical service upgrades, plumbing vents, and gas work. Always budget 10-15% contingency for inspections that require remediation and potential geotechnical work.
Three Portland accessory dwelling unit (adu) scenarios
Oregon state law override vs. Portland zoning: what changed in 2019 and why your neighbor's old ADU denial letter is worthless now
Before 2019, Portland zoning code (Title 33) made ADUs administratively difficult: they required the owner to occupy the primary residence (owner-occupancy mandate), they often ran into lot-size minimums (1 acre for detached ADU) and setback penalties that made them economically unviable, and parking requirements forced most applicants to find space they didn't have. In July 2019, Oregon's HB 2001 (which became ORS 197.312) overrode all of that statewide. The law mandates that every city must allow at least one ADU per single-family lot, no owner-occupancy requirement, no minimum lot size restrictions beyond what exists for the primary dwelling, and no parking mandate for the ADU itself. Portland's response was immediate: by September 2020, it had adopted amendments to Code 33.205.040 and deleted the old owner-occupancy clause, raised lot-size thresholds, and eliminated ADU-specific parking requirements.
The practical outcome: if you submitted an ADU application in Portland in 2015 and were denied because of 'owner-occupancy requirement,' that denial is legally void now. If a neighbor tells you ADUs aren't allowed on single-family lots, they are wrong — Oregon law now mandates that they are. What the city CAN still enforce: setback minimums (5 feet for detached ADU vs. 10 feet for the main house), lot coverage limits (detached ADU cannot exceed 35% of lot size), height limits (25 feet for detached ADU in R7 zones, 35 feet in R5), and separation from the main dwelling (typically 10 feet). These are design constraints, not permission denials. If your lot is 2,500 sq ft and you want to build an 800 sq ft detached ADU, the lot-coverage rule allows only 875 sq ft maximum (35% of 2,500). You'll need to shrink your ADU to ~800 sq ft or use a junior ADU (carved inside the main house or above a garage) instead, which has a 500 sq ft cap and more lenient lot-coverage treatment.
One more nuance: the state law applies within Portland city limits. If your address is in unincorporated Multnomah County, East County, or Gresham, you're under a different jurisdiction's code. East Gresham and outer East County follow Clackamas County zoning, which also adopted Oregon's mandate but has slightly different lot-size and setback rules. Always confirm your jurisdiction in PortlandMaps or by calling the County Assessor; the wrong agency will delay your application by 4-6 weeks.
Preapproved plans, geotechnical workarounds, and the $2,000–$3,000 shortcut most Portland applicants miss
In 2021, Portland's Bureau of Development Services (BDS) created a library of preapproved ADU plans to fast-track the permitting process. These are fully engineered, one-size-fits-most designs (typically 800 sq ft detached, or 500 sq ft junior ADU conversion templates) that have already passed plan review and comply with all Portland code and IBC requirements. The catch: they're only 'preapproved' if your lot matches the template's assumptions. For Willamette Valley lots (west Portland, downtown, SW Hills) with 12-inch frost depth and typical alluvial/volcanic soils, the 'Willamette Standard Detached ADU' template fits most applicants. For East County lots with 30-inch frost depth and expansive clay, the 'East County FPSF Detached ADU' template is designed with frost-protected shallow foundation (FPSF) built in, which eliminates the need for a geotechnical report and the $800–$1,500 engineering fee a custom design would require.
The permitting speed is the real win: a preapproved plan compresses plan review from 8-12 weeks to 25-30 days (BDS calls this 'expedited review'). You still need a stamped plan preparer (licensed engineer or architect) to add your address, lot dimensions, and any site-specific notes (~$400–$600 cost and 1 week turnaround), but you're not paying for a full custom design. For an applicant with a $150,000–$200,000 ADU budget, saving $2,000–$3,000 in design fees and 6-8 weeks in timeline is meaningful. The BDS website lists which template your lot qualifies for (check by address and frost depth/soil). If your lot has unusual constraints — steep slope, wetland/riparian overlay, or expansion of an existing non-conforming building — preapproved plans won't work, and you'll need custom design.
Geotechnical reports (soil boring, compaction test, report) cost $500–$1,200 and take 2-3 weeks to obtain. If you're in an area where expansive clay is standard (East County, outer SE), a geotechnical report can either confirm that the preapproved FPSF design is safe (no extra cost) or reveal that your specific lot has perched groundwater or subsidence risk (which requires a custom foundation design and engineering, $1,500–$3,000 extra cost). Many Portland applicants skip the geotechnical report and use the preapproved template anyway — this is usually safe, but it's a compliance risk if inspectors find settlement issues later. The smart move: if you're using a preapproved plan, pay $500–$800 for a simple geotechnical confirmation; if you're designing custom, budget for full geotech upfront. Either way, you'll know before construction whether your foundation plan is sound.
1900 SW 4th Ave, Suite 5000, Portland, OR 97201
Phone: (503) 823-7300 | https://www.portlandoregon.gov/bds/ (PortlandMaps and online permit tracking)
Monday–Friday, 8:00 AM–5:00 PM (permit counter closes 4:30 PM; online portal open 24/7)
Common questions
Do I have to live in the main house if I own an ADU in Portland?
No. Oregon state law (ORS 197.312, effective 2019) eliminated owner-occupancy requirements, and Portland code 33.205.040 reflects this. You can own both the primary house and ADU, live in the ADU and rent the main house, or rent both. The only restriction is that you cannot have more than one ADU per single-family lot — the state law allows 'at least one ADU,' but Portland hasn't authorized more than one yet. If you're a non-owner investor looking to finance an ADU, lenders may have separate underwriting rules, but the city permit itself has no occupancy mandate.
Can I use a preapproved plan if my lot is in a historic district?
No. Preapproved plans are designed for standard zoning and bypass Historic Design Review. If your lot is in a historic overlay (Laurelhurst, Nob Hill, Mt. Tabor, King's Hill, etc. per PortlandMaps), any ADU that's visible from the street or alters the existing historic structure requires a Design Review and possibly a Historic Landmarks Review (4-6 weeks, $800–$1,200 fee). You'll need a custom design that respects the historic character (period windows, matching materials, etc.), which cannot be templated. This adds cost and timeline but is non-negotiable if you're in a historic district.
What happens if my lot is in a floodplain or has a riparian buffer zone?
Portland's floodplain overlays (100-year and 500-year) and riparian buffers (streams, wetlands) are mapped in PortlandMaps. If your ADU site is in a 100-year floodplain, you'll need elevation certificates and possibly pile foundation or fill to meet FEMA requirements (add $2,000–$4,000 and 2-3 weeks for geotechnical and structural engineering). Riparian buffers require a 15-foot setback from the stream; if your ADU footprint violates this, you'll need a variance or site redesign. Neither floodplain nor riparian triggers an automatic denial, but both require additional planning and engineering. Check PortlandMaps before finalizing your ADU footprint.
Do I need to provide parking for an ADU in Portland?
No. Oregon state law and Portland code waived the parking requirement for ADUs. However, if your primary dwelling already has substandard or zero off-street parking, the city may flag it at final inspection as an enforcement issue (not a permit-blocking issue). In practice, most Portland single-family lots have at least one driveway space; if you're converting a garage and losing parking, discuss it with your plan reviewer upfront, but you won't be denied a permit because of it. Rental market and tenant expectations are separate from code — many renters expect parking, so you may want to provide it anyway for marketability.
What are the differences between a detached ADU, a garage conversion, and a junior ADU?
Detached ADU: a new, separate building (up to 800 sq ft in Portland) on the same lot, with its own foundation, roof, entrance, and utilities. Requires full building permit and plan review (8-12 weeks). Garage conversion: converting an existing detached garage into a dwelling (typically 500-800 sq ft depending on the garage size); no new foundation, simpler plan review (6-8 weeks). Junior ADU (also called 'accessory dwelling unit carved out of existing structure'): a space created inside the main house or above a garage (max 500 sq ft, typically one bedroom or studio) with a separate entrance, kitchen, and utilities. Fastest to permit (6-8 weeks) because you're not building new structure. All three require separate utilities and full building permits; none are exempt.
How much does a building permit for an ADU cost in Portland?
Portland's permit fee is typically $800–$1,200 for the base building permit (scaled by ADU square footage and complexity). System Development Charges (SDCs) for new water/sewer service run $2,000–$3,500 depending on meter size and line length. Plan review is included in the permit fee if you file online. If you need a geotechnical report ($500–$800) or Historic Design Review ($800–$1,200), add those separately. Total permitting cost (permit, SDCs, and routine inspections) is typically $3,000–$4,500 for a standard detached ADU. Preapproved plans may reduce the total to $2,500–$3,500. Construction cost (labor + materials) is separate, typically $120–$180 per square foot in Portland (2024), so an 800 sq ft ADU costs $96,000–$144,000 to build.
Can I be my own contractor (owner-builder) for an ADU in Portland?
Yes, if you own the lot and occupy the primary residence on the same lot. Oregon law and Portland code allow owner-builders for residential construction including ADUs, provided you're building for yourself (not as a contractor for hire). You'll still need to hire licensed trades for electrical service upgrades (licensed electrician required for service panel work), plumbing vents and gas (licensed plumber/gasfitter), and HVAC if applicable. Building permit, inspections, and occupancy requirements are the same as contractor-built ADUs; you just save labor costs on framing, drywall, painting, etc. If you're not the owner-occupant of the primary dwelling, you cannot use owner-builder authority — you must hire a licensed contractor.
How long does plan review take for an ADU in Portland, and can I start construction before I get the permit?
Standard plan review is 8-12 weeks for a custom design; preapproved plans are 25-30 days. You cannot legally begin any construction (excavation, foundation, framing, etc.) until the building permit is issued and posted on-site. If the city finds unpermitted work, you'll be issued a stop-work order, fined $500–$5,000, and required to bring the work up to code at additional cost ($8,000–$15,000 typical remediation). Utility work (sewer/water connection to the main line) cannot begin until the utility inspector approves it, which happens after building permit is issued. Budget 4-5 months from permit issuance to final occupancy for a standard detached ADU; 2-3 months for a garage conversion.
What if my ADU will have a separate entrance but share utilities with the main house (sub-metering instead of separate meters)?
Sub-metering (a single water or sewer meter split between the main house and ADU via a dual-meter fixture) is allowed in Portland if the city approves it in advance. It's less common than separate meters because it complicates future separation (if you want to sell just the ADU, or if utilities need maintenance). If you propose sub-metering, discuss it with BDS in the intake phase (before full plan review). Some inspectors will require you to convert to separate meters later if disputes over utility bills arise between tenants. The safest approach: plan for separate meters upfront. The cost difference is minimal (~$300–$500 for the extra meter vs. sub-meter fixture), and you'll avoid plan-review back-and-forth.
If my ADU will be in an East County lot with expansive clay soil, do I have to get a geotechnical report?
Not if you use a preapproved plan that's already engineered for expansive clay (the 'East County FPSF Detached ADU' template). If you're designing custom, a geotechnical report ($500–$1,200, 2-3 weeks) is strongly recommended because expansive clay requires either frost-protected shallow foundation (FPSF) or deeper conventional footings. The city inspector will likely ask for geotech evidence; if you don't have it and your foundation shows cracks or settlement later, remediation can cost $10,000–$30,000. Budget for geotech upfront; it's cheap insurance. If your lot has already been tested for the primary house, you can often reference that report for the ADU foundation design.