Best ADU Builders Portland (2026): How to Choose a Contractor Who Knows Chapter 33.205
Bottom line up front.
If you are searching for the best ADU builders in Portland in 2026, the key qualifier is this: does the builder know Portland Zoning Code Chapter 33.205, can they assess your lot's compliance with the 800 sq ft / 75% living-area cap for detached ADUs, and can they confirm placement compliance before the first plan is drawn? Portland has one of the more detailed ADU zoning codes in the Pacific Northwest. Builders who misread the size cap, the placement requirement (behind the primary dwelling's rear wall or 40 feet from the front property line), or the setback standards will either design something that requires costly revisions or fail plan check entirely.
No builder can guarantee permit approval or timelines. Portland's Bureau of Development Services (BDS) review times vary. Verify current information with BDS before committing to any timeline or signing a contract.
Source: The Dwelling Index independent research; City of Portland Bureau of Development Services; Portland Zoning Code Chapter 33.205. Last verified: June 12, 2026.
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Portland ADU size limits and placement requirements
Portland Zoning Code Chapter 33.205 establishes the primary parameters for ADU development:
| Parameter | Portland standard (verify with BDS) |
|---|---|
| Detached ADU max size | 800 sq ft of living area or 75% of primary dwelling's living area, whichever is less |
| Attached ADU max size | 75% of primary dwelling's living area; no absolute cap |
| Detached ADU placement | Behind the rear wall of the primary dwelling, or ≥40 ft from front property line |
| Setbacks | Rear: typically 5 ft; side: typically 5 ft; verify by zone |
| Height | Typically 15–20 feet depending on zone and proximity to lot lines |
| Pre-approved DADU plans | Available from Portland BDS; site-specific review still required |
| Permit pathway | Building permit through BDS; site-specific review for all projects |
Always verify current requirements with Portland's Bureau of Development Services. Zoning code is updated periodically.
Portland's pre-approved DADU plan program
Portland Bureau of Development Services offers pre-approved DADU plan sets that reduce the plan-review phase:
- Pre-reviewed base design. The plan set's base structural, architectural, and code compliance has been reviewed. This reduces the plan-check cycle compared to a full custom review.
- Site-specific review still required. Setbacks, grading, drainage, utility connections, and any site-specific conditions must still be reviewed and approved independently of the pre-approved design.
- Design modifications exit the pathway. If the pre-approved design is modified — different foundation type, enlarged footprint, structural changes — the project may exit the pre-approved pathway and require full review.
- Tree protections. Portland has significant urban tree protection requirements. If your lot has significant trees, a separate tree permit may be required that affects ADU siting.
Budget in hand — now find the right financing path.
Most Portland ADU projects are financed with a HELOC, cash-out refinance, or construction loan. Each has different rate behavior, draw timing, and tax treatment.
Compare ADU Financing Paths →Financing-path education; we don't quote rates as guarantees.
Utility and site costs in Portland DADU projects
Portland ADU projects regularly encounter utility and site cost variables not captured in base construction quotes:
- Portland Water Bureau and sewer connection. Adding an ADU may require a new water meter or water service upgrade. Bureau of Environmental Services (BES) sewer connection fees apply for new dwelling units.
- Portland General Electric (PGE) or Pacific Power service upgrade. If your panel does not have capacity for a second dwelling, an electrical service upgrade is required. Cost varies by existing service and utility company.
- Stormwater management. Portland has stormwater management requirements for impervious surface additions. New ADU construction adds impervious area — a stormwater management plan may be required for projects above the stormwater threshold.
- Tree permits. Removal of a significant tree (>12 inches diameter at breast height for most Portland zones) requires a separate tree permit and potential mitigation planting.
- SDC (System Development Charges). Portland charges system development charges for transportation, parks, and water/sewer for new dwelling units. Ask your builder for a current SDC estimate — it can be $10,000–$25,000+ depending on the ADU size and location.
Seven questions to ask every Portland ADU builder
- Can you walk me through Chapter 33.205 and how it applies to my lot? A prepared builder can explain the size cap, placement requirement, and setbacks for your specific zone.
- How many ADU permits have you pulled with Portland BDS? Ask for permit numbers you can look up in PortlandMaps.
- Is my lot eligible for a pre-approved DADU plan? Can they explain the eligibility criteria and confirm whether your lot qualifies?
- Does your quote include Portland SDCs? Ask for a current SDC estimate broken out by system (transportation, parks, water/sewer).
- Are there significant trees on my lot? What is the tree permit process and how could it affect ADU siting?
- What is your Oregon CCB license number? Verify at oregon.gov/ccb — active license, correct type, current bond and workers' comp.
- Can you provide three verified Portland ADU references? Ask for PortlandMaps permit numbers you can look up independently.
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Download the Free ADU Starter Kit →Frequently asked questions
What is the maximum ADU size for a detached unit in Portland?
Under Portland Zoning Code Chapter 33.205, a detached ADU in Portland is limited to 800 square feet of living area, or 75% of the primary dwelling's living area, whichever is less. This cap applies to living area (not total building area including garages or accessory spaces). A builder who quotes a detached ADU larger than this limit is either working from outdated information or misquoting the applicable code.
Where must a Portland detached ADU be placed on the lot?
Portland Zoning Code requires that a detached ADU be placed behind the rear wall of the primary dwelling or at least 40 feet from the front property line, whichever is less restrictive. This placement requirement is designed to maintain the character of the primary dwelling as the dominant structure from the street. Lots with unusual configurations may require specific siting analysis.
Does Portland have a pre-approved DADU plan program?
Yes. The City of Portland's Bureau of Development Services (BDS) offers pre-approved DADU plan sets that can reduce the plan-review cycle. Pre-approved plans have been pre-reviewed against Portland's base code requirements. Site-specific review — setbacks, utility connections, grading, tree protections — is still required for every project. Eligibility for the pre-approved pathway depends on lot configuration, topography, and whether the design can be used without modification.
What is Portland Zoning Code Chapter 33.205?
Chapter 33.205 of the Portland Zoning Code governs accessory dwelling units. It establishes the allowed locations, size limits, placement requirements, design standards, and permit process for both detached DADUs and attached AADUs in Portland. Builders claiming Portland ADU experience should be able to cite this chapter and explain the specific standards for your zone and lot configuration.
Are Portland ADUs eligible for Freddie Mac or Fannie Mae ADU financing?
Portland ADUs that meet applicable code requirements — permitted, on a permanent foundation, with a separate entrance — are generally eligible for consideration under Freddie Mac's and Fannie Mae's ADU-inclusive appraisal and lending guidelines. However, lender-specific requirements vary, and not all Portland ADU configurations will qualify. Confirm with your specific lender before committing to a financing strategy based on ADU rental income or appraised ADU value.
How do I verify a Portland ADU builder's Oregon CCB license?
All contractors performing construction work in Oregon must be licensed with the Oregon Construction Contractors Board (CCB). Verify CCB license status at oregon.gov/ccb. Confirm the license type covers your project (residential general contractor for most ADUs), the license is active, the bond is current, and workers' compensation coverage is in place. Also ask for a certificate of general liability insurance. Do not rely on a contractor's verbal claim of being licensed — always verify independently.
Editorial independence: The Dwelling Index does not accept payment for builder placement. No builder mentioned in this guide has paid for inclusion, ranking, or editorial coverage. All guidance is based on independent research. Regulations change; verify all information with Portland's Bureau of Development Services before signing a contract.