Square Footage, Sticker Shock, and What Your Backyard Could Be Worth
Is your property quietly sitting on thousands of monthly rental income? Could a backyard build really add extra living space for your family?
Here is what we will cover in this post: real Portland ADU cost ranges by type, the line items most homeowners miss, and how to keep your budget honest from design through final inspection.
By the end, you will know exactly what to budget for an ADU construction project and how to spot a price that does not add up.
How Much Does it Cost to Build an ADU in Portland?
A new ADU in Portland typically costs between $290,000 and $500,000, depending on whether you build detached, attached, or a conversion.
- Detached units run $290,000 to $500,000.
- Conversions of garages, basements, or interior space run $150,000 to $300,000.
- Attached units run $325,000 to $500,000.
These ADU construction costs assume a complete dwelling unit with a full kitchen, bathroom, and independent utilities, which is what an ADU actually is. They can take between 12 and 20 weeks to build, not including the design phase.
Detached ADUs
Detached units give you the most flexibility for rentals or multigenerational living.
THE Remodel Group builds them as full new-construction projects.
Foundation, framing, utilities, and finishes are all designed and priced from the ground up, so there are no surprises mid-build.
On properties near green corridors like Forest Park, site access and slope can push costs higher.
Attached ADUs
Attached units share at least one wall with your primary residence and are built as additions.
Costs are a touch higher than detached because of the structural integration and shared utility work.
When zoning or lot size makes a detached unit impossible, this is often the most practical path to rental income or additional living space.
Conversions: Garage, Basement, and Interior
Conversions look cheaper on paper, and that is where most homeowners get burned.
Garages and basements were not originally built to housing code.
Once we add the required electrical wiring, insulation, ceiling height adjustments, and structural work, the expected savings often disappear entirely.
Here’s a garage conversion we did in Portland.
Pre-Construction and Soft Costs for ADUs
Before a single nail goes in, every ADU project needs to put real money into design and engineering.
Plan to spend $9,000 to $25,000 on the pre-construction phase.
- Architectural design: $5,000 to $15,000.
- Structural engineering: $2,000 to $5,000.
- Energy modeling: $500 to $1,500.
- Site survey: $800 to $2,000.
- Soil testing: $1,000 to $3,000.
We run a two-phase design-build process where we lock in fixed pricing after design development.
That means your budget is set before construction starts, not estimated as we go.
Portland Permits, Fees, and the SDC Waiver
Permits are a major part of ADU costs here in Portland.
Plan for 35,000 to $28,000 combined for permits and fees.
- Building permits: $2,000 to $5,000.
- Plan review fees: $1,000 to $3,000.
- System Development Charges: $0 to $15,000.
The SDC waiver can save you the full SDC amount if you sign a covenant agreeing not to use the ADU as a short-term rental for 10 years.
What Drives ADU Costs the Most
The biggest cost driver is the type of ADU you build.
After that, it comes down to size, site conditions, and finish level.
Smaller ADUs cost more per square foot than larger ones, because the kitchen, bathroom, and permitting fees do not shrink when the floor plan does.
Lot conditions matter just as much.
A flat, accessible site with city utilities at the property line will always pencil cheaper than a sloped lot near a green corridor that needs extensive site work.
Finish level is the last big lever.
Mid-range finishes hold their value, look good, and keep your numbers predictable. Lower-tier finishes tend to look cheaper and/or not last as long.
What makes an ADU luxury vs not?
How to Control ADU Construction Costs Without Cutting Quality
You can keep your ADU budget honest without giving up quality.
- Finalize your design before construction starts.
- Limit unnecessary square footage.
- Reuse existing space when it makes sense.
- Choose durable, mid-range finishes.
- Understand your financing options early.
Most cost guides will tell you to set aside 10% to 15% of your total project budget as a contingency fund for unexpected costs.
We think that is too much for a design-build project.
When your builder is involved from day one of design (like we are when you work with us), the accuracy of project costs, labor costs, and materials costs goes way up, and the need for a giant contingency reserve goes down.
We back our work with a 2-year craftsmanship warranty on every ADU we build.
Return on Investment: Property Value and Rental Income
A well-built ADU typically adds 60% to 80% of its construction cost back to your home’s value.
Potential rental income for a Portland-area ADU usually lands between $1,500 and $2,500 a month.
The bigger win is what an ADU gives you beyond generating rental income.
You get a real wealth-building asset, room for aging parents or adult children, and a property that becomes more flexible as your life changes.
Because most ADUs sit behind the primary dwelling, the real value lies in the appraisal and the income, not the curb appeal.
Financing Your Portland ADU Construction Project
Homeowners in Tigard, Beaverton, and Portland can fund their ADU through a combination of home equity and construction financing.
Common options include:
- Home equity line of credit.
- Cash-out refinance.
- Dedicated construction loan.
- ADU-specific loan product from local lenders.
Sort out financing before design, not after, because a locked-in project budget is only useful if your funding is locked in, too.
Backyard Dreams, Real Budgets, and Better Builds with THE Remodel Group
We build ADUs across Portland, Beaverton, Lake Oswego, and Tigard using a two-phase design-build process that locks in fixed pricing before construction starts. That front-loaded design is exactly how we keep the numbers in this guide from drifting on real projects.
When you are ready to see what your lot and budget can actually do, fill out our contact form today or give us a call to start with a discovery call and on-site consultation.
From there, we walk you through Phase 1 design exploration and Phase 2 design development, with locked pricing waiting at the end.
