ADU & Accessory Structures Inspection:
Portland Agent Guide
ADUs are common in Portland transactions and they’re not automatically part of a standard home inspection. Here’s what agents need to understand about scope, what inspectors check, and what tends to come up.
Portland has a lot of ADUs. The city’s zoning changes over the past decade made them easier to build, and conversions of garages, basements, and backyard spaces have been happening at a steady pace. For agents, that means a significant share of residential transactions involve a secondary unit.
The problem is that ADUs are frequently not included in what buyers think they’re getting when they schedule a home inspection. And when they are included, a lot of what matters in a conversion project goes unexamined unless the inspector knows to look for it.
This post covers how ADU inspections work, what inspectors document, and what agents should know before the report comes in on a property with a secondary unit.
What Gets Included, and What Doesn’t
This is where agents make the most mistakes with ADU transactions. A standard home inspection covers the main structure. An ADU is usually not included by default unless it shares systems with the main house in a way that makes separation impractical.
An attached ADU, such as a basement unit or a ground-floor addition that shares the main electrical panel and furnace, may be largely covered by a standard inspection. But the living areas of the ADU still deserve specific attention: ceiling height, egress, electrical within the unit, smoke and CO detectors in sleeping areas, bathroom plumbing.
A detached ADU (a backyard cottage, a converted detached garage, a DADU) is its own structure. It has its own foundation, roof, electrical service or subpanel, heating equipment, and plumbing connections. None of that is covered by the main house inspection. A buyer who wants the detached ADU inspected needs to add it to the scope at booking.
At Trusted Home Inspections, ADUs are custom quoted based on size and complexity. The detached structure fees ($50 small, $100 large) applies to small unfinished buildings like sheds and garages, not to a finished ADU. Either way, the cost is small relative to what an undocumented structure can turn into.
What the Inspector Looks at in an ADU
The inspection categories are the same as for any structure. The emphasis shifts based on what type of ADU it is.
For a converted garage, framing and foundation get attention first. Garage slabs are typically not insulated and sometimes have drainage problems when converted to living space. The inspector checks whether adequate insulation was added to walls and ceiling. Garage doors that were replaced with framed walls get checked for proper construction.
Electrical is often the most significant findings category in ADU conversions. Conversion projects frequently involve electrical work that was done without a permit, by unlicensed contractors, or by handy owners. Subpanel installation quality, wiring methods, circuit load, GFCI protection in kitchens and bathrooms, and smoke and CO detector placement all get checked.
Plumbing in an ADU conversion gets inspected at visible connections: under sinks, at the water heater if present, at any exposed drain lines. Full sewer and supply pipe conditions behind walls aren’t visible without destructive access, but the inspector documents what they can see.
HVAC matters a lot in ADUs. Ductless mini-splits are a common heating solution in Portland-area ADU conversions. A professionally installed unit is a good system. A self-installed unit with improper mounting, refrigerant line exposure, or missing condensate drainage is a finding. The inspector checks operation and installation quality.
Egress is a specific concern in sleeping areas. Oregon requires bedrooms to have at least one emergency escape window meeting minimum size and opening requirements. Basement conversions are where this comes up most. A converted basement bedroom with a small, fixed window may not have compliant egress.
Converted Garages: The Most Common ADU Type
Portland has a lot of converted garages. They range from professionally permitted projects with proper insulation, electrical, and HVAC to rough weekend projects with drop ceilings, extension cords run through the walls, and a space heater plugged into a 15-amp circuit.
The quality range is wide. An inspector can usually tell within five minutes which end of that range they’re dealing with.
What to expect on a professionally converted garage: proper stud wall construction where the garage door used to be, insulation in walls and ceiling, a mini-split or other dedicated heating system, a dedicated electrical circuit for kitchen and bathroom needs, GFCI protection, code-compliant egress if there’s a bedroom, and proper permits on record.
What to expect on a DIY conversion: missing permits, insulation stuffed between studs without vapor management, mismatched wiring, bathroom fans vented into the attic or ceiling cavity instead of outside, window wells without proper sizing for egress, and heating from a single plug-in unit.
The inspector documents what they find. Findings don’t automatically mean the structure is unusable, but buyers deserve to know what they’re getting.
ADU patterns that come up in Portland-area inspections
- Unpermitted garage conversions are very common in inner Portland neighborhoods, North Portland, and parts of SE Portland
- Mini-split systems installed without proper condensate management show up regularly in newer conversions
- Basement ADUs with insufficient ceiling height (below 7 feet) are common in pre-1970 homes
- Missing egress windows in converted basement sleeping areas is one of the most frequently flagged safety conditions
- Older garage conversions often have knob-and-tube or aluminum branch circuit wiring routed from the main structure
- Properties marketed with ADU rental income often have conversion work that hasn’t been permitted
Real Inspection Photos
Converted Garage Details Inspectors Check
Real photos from Russ's reports of garage and basement conversion details.
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A converted garage room with no wall outlets. Without outlets, occupants tend to lean on extension cords and power strips. -
The door from the garage to the living space didn't meet fire separation standards. A rated, self-closing door is the usual fix. -
Basement bedroom windows too small or too high for emergency escape. Egress comes up most in converted basements.
Purpose-Built ADUs and What to Expect
A purpose-built ADU, designed as a separate dwelling from the start and permitted as such, is a different story. These are more likely to be built to current code, inspected by the jurisdiction during construction, and well-documented.
That doesn’t mean there are no findings. Purpose-built ADUs still have systems that can deteriorate, installation quality issues, and conditions that develop over time. But the starting point is usually better than a converted structure.
The inspector looks at the same things: structure, roof, electrical, plumbing, HVAC, and livability conditions. For a detached backyard cottage with independent utility connections, the water and sewer connections to the street may go through the main house’s systems or may be independent. That matters for understanding how the systems work and what the maintenance responsibilities are.
What Agents Should Do Before the Transaction Closes
Get clarity on scope before booking. If the property has an ADU, attached or detached, confirm with the buyer that it’s part of the inspection. If it’s a detached ADU, ask for a custom quote when booking. Don’t assume.
Pull permit history. A property history report ($25 add-on with the inspection, pulling permit records from BuildFax and BuildChek) or a county records search can tell you what permits were pulled for the ADU. An unpermitted ADU isn’t automatically a problem, but buyers should know what they’re inheriting.
Set expectations about conversion quality. If the ADU is a converted garage that looks like it was done quickly and cheaply, there will be findings. Agents who walk the property before listing and think critically about the conversion quality can prepare their clients better.
For pre-listing inspections on properties with ADUs, the pre-listing home inspection page covers how to scope and book that properly.
Buyers purchasing properties with ADUs can find information about what’s included in the standard inspection on the buyer’s home inspection page. To add a detached ADU to the inspection scope, ask for a custom quote when scheduling. Book online or contact Trusted Home Inspections directly.
ADU Inspection Portland FAQ
