Portland’s ADU inventory has grown significantly over the past decade, driven by city policy changes that encourage accessory dwelling units as a response to housing supply constraints. Detached backyard cottages, garage conversions, basement apartments, and attached secondary suites are now common in Portland transactions. Buyers purchasing properties with ADUs need to understand what an inspection covers, what permit status means for their transaction, and how the rental income potential of an ADU is affected by its legal standing. Agents who know this territory serve their clients more accurately.
What the Inspection Covers in ADU Transactions
When a property includes an ADU, the inspection scope typically covers both the primary residence and the accessory unit. Each unit is evaluated for the same systems and components: structure, roofing (if separate), exterior, electrical, plumbing, HVAC, insulation and ventilation, and interior components. The ADU generates its own findings that are separate from the main house findings, and buyers should review the report with both structures in mind.
Common ADU findings in Portland’s older stock include aging electrical panels or service that is insufficient for a full living unit, plumbing that was added without proper venting, inadequate egress in sleeping areas, insulation deficiencies in garage conversions, and moisture issues in basement units. A garage conversion that was done with care and proper permits may be in excellent condition. One that was done informally by a previous owner may have significant deficiencies behind finished walls that only become apparent through careful inspection and thermal imaging.
Permit Status and Legal Dwelling Status
The most consequential question in an ADU transaction is usually whether the unit is a permitted legal dwelling. Portland Bureau of Development Services issues ADU permits and maintains records. An ADU that was permitted, inspected, and received a final certificate of occupancy is a legal dwelling that can be lawfully rented. An ADU that was built without permits is not a legal dwelling regardless of how well it was constructed or how long it has been rented.
The inspection does not verify permit status. Inspectors evaluate physical condition as they find it. Buyers who want to confirm an ADU’s legal standing should pull the permit history from Portland BDS or the relevant jurisdiction. This is important for several reasons. A buyer who purchases a property expecting rental income from a non-permitted ADU may discover they cannot legally rent it, or that it requires significant work to bring into compliance before it can be permitted. Lenders also treat non-permitted ADUs differently in appraisals: a non-permitted unit typically cannot be counted in the property’s income potential for loan qualification purposes.
Basement and Garage Conversion ADUs
Basement and garage conversions are the most common informal ADU type in Portland’s existing housing stock. They vary enormously in quality. Some were built by skilled contractors with permits. Others were built by owners who did their best without professional involvement. The quality of work in an informal conversion is often apparent to an inspector who knows what to look for: amateur electrical work, improper venting on plumbing, insulation that does not meet minimum requirements, and egress windows that do not meet code for sleeping rooms.
Thermal imaging is particularly valuable in garage and basement conversions because it reveals insulation deficiencies and moisture patterns behind finished walls that would not otherwise be visible. Trusted Home Inspections includes thermal imaging at no extra charge on every inspection.
Detached Backyard Cottages
Detached ADUs, often called backyard cottages or DADUs, are inspected as separate structures when they are included in the property. A well-built detached cottage with its own foundation, electrical service, plumbing, and HVAC is a more complete structure to inspect than a garage conversion, and findings should be understood in that context. The structure, roofing, electrical, plumbing, and HVAC of the detached unit are all evaluated. Buyers purchasing properties with detached ADUs should budget the same due diligence time and consideration for the ADU as they would for the main house, because the ADU is a second property in terms of systems complexity.
Working With Trusted Home Inspections
ADU inspections are included in the standard scope when the unit is part of the property being purchased. Thermal imaging is included at no extra charge and is particularly valuable in finished conversion spaces. Certified Master Inspector dual-licensed in Oregon and Washington, same-day reports, 7-day scheduling.
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