Skip to main content Skip to content Real 2026 Portland pricing for garage conversions, attached suites, and detached backyard cottages, with a working calculator and itemized budgets from a 5.0-rated design-build firm.
Building an ADU in Portland runs $135K to $475K+ in 2026, depending on whether you convert an existing space or build new. A basement or garage conversion is the most cost-effective path, often $135K to $180K, because it reuses an existing structure. A detached backyard ADU, the iconic Portland cottage, most commonly lands between $280K and $360K (about $300 to $450 per square foot) because it is a new building with its own foundation, roof, utilities, kitchen, and bath. ADUs may also trigger System Development Charges, though many qualify for exemptions or waivers depending on size and use, so confirm your fees early. The five ranges at right reflect real WCG ADU builds across the Portland metro.
Cost CalculatorAn ADU is the rare Portland project that pays you back: a legal, rentable home in your own backyard, built once and yours for decades. The number on the 2026 estimate reflects the type you choose and how it is built.
Ten real-world levers tuned to Portland ADU project data. Choose your ADU type, finish level, and scope, and the live estimate updates with every selection. Your choices carry into the consultation form.
This is an estimate built on 2026 Portland data. For the true cost of your ADU, schedule a free in-home estimate.
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Estimate range based on 2026 Portland project data. Final pricing requires an in-home consultation and itemized estimate, delivered within one business day.
Every line on a WCG ADU estimate ties back to one of these six factors. Some you control. Some the property tells us.
The single biggest driver. A garage or basement conversion reuses an existing shell. A detached ADU is ground-up construction with its own foundation, roof, siding, and utilities, which is why it costs the most.
More square footage means more foundation, framing, roof, and finish. Portland allows up to 800 sq ft by right. A second story or a 1,000 sq ft unit adds a staircase, more roof, and more structure on top.
A flat lot with a simple utility tie-in is the easy case. Sloped Portland lots, poor soil, tree-root protection, and a long run of water, sewer, and power out to a detached unit all add real cost.
A full kitchen plus a full bath is the costliest part of any ADU. Finish grade swings it widely, from a builder-grade kitchenette and a simple full bath to a custom kitchen and a tiled spa bath.
System Development Charges, which some ADUs can have exempted or waived by size and use, plus separate water, sewer, and electrical and Portland's permit and plan-review fees. The schedule updates annually.
Design-build means one contract for design, permitting, and construction. You get an itemized estimate before the foundation is poured, fewer change orders mid-project, and a price that holds because the scope is set first.
A Portland ADU can land at $135K, $300K, or $475K depending on whether you convert an existing space or build new, and how it is finished. The choice is not better or worse. It is what fits your lot, your budget, and how you plan to use it.
Four ADU types cover most Portland projects in 2026. The cost is driven first by the type, conversion or new build, then by square footage and finish level. The table below maps each type to its per-square-foot range and a typical 2026 total.
| ADU Type | Per Sq Ft | Typical 2026 Total |
|---|---|---|
| Basement Conversion ~600 sq ft | $150 to $225 | $135K to $160K |
| Garage Conversion ~500 sq ft | $175 to $275 | $145K to $180K |
| Attached ADU ~650 sq ft | $250 to $375 | $240K to $320K |
| Detached ADU ~700 to 800 sq ft | $300 to $450 | $280K to $475K+ |
Ranges reflect 2026 Portland metro projects. A larger unit, a second story, or a difficult site pushes toward the high end of each type.
The price differences are not abstract. They sit in the structure, the exterior, the outdoor living, and the interior fit-out. Here are the four choices that most often shape a detached ADU.
A standalone unit with its own foundation, roof, and entrance, set into your backyard. It reads as a small home, not an add-on, with its own address, its own utilities, and the privacy a separate building gives a tenant or family member.
A detached ADU is the most expensive type because it is ground-up construction, commonly $300 to $450 per square foot. The structure itself, the foundation, framing, roof, and shell, is the largest share of that cost.
The exterior is where an ADU either disappears into the yard or becomes a design feature. Lap or panel siding, clean modern rooflines, large windows for light, and a color palette that either matches the main house or stands on its own.
Upgraded siding, windows, and a more complex roof move the exterior cost up. A simple gable with builder-grade siding keeps it down. The exterior shell is part of why detached units cost more than a conversion.
A covered porch or deck turns an ADU from a box into a home. It gives a tenant or family member a private outdoor space, shelters the entrance from Portland rain, and makes a small footprint feel larger by extending the living area outside.
A covered porch or deck is an add-on, commonly around $18K depending on size and finish. It is one of the upgrades that most changes how the finished ADU lives day to day.
Inside, an ADU is a complete home in miniature. A full kitchen, a full bath, a living area, and one or two bedrooms, all fitted into a compact, efficient footprint. The interior fit-out is where finish level swings the budget the most.
A full kitchen plus a full bath is the costliest part of any ADU, a $25K to $80K range depending on grade. A builder-grade kitchenette and simple bath keep it lean. A custom kitchen and tiled spa bath move it to the top.
Recent Portland ADU projects, from detached backyard cottages in Beaverton to garage-conversion rentals in Southeast Portland. Each one started as a 2026 estimate and an honest conversation about budget.
See Full GalleryBelow are itemized 2026 budgets for the three most common Portland ADU paths: a detached new build, an attached suite, and a garage conversion. Representative scope and pricing for each type.
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The visible scope is the building, the kitchen, and the bath. The complete 2026 budget covers eight more line items that catch homeowners off guard the first time they price an ADU. We itemize all of them in the estimate.
Schedule Free ConsultationADUs can trigger SDCs, but many qualify for exemptions or waivers by size and use. Confirm your fees with the city early; the schedule updates annually.
Running water, sewer, gas, and electrical from the house or street out to a detached unit. Separate meters add cost.
Sloped Portland lots, drainage, tree-root protection, and excavation for a detached foundation. The lot itself drives this line.
Building, electrical, plumbing, and mechanical permits plus Portland plan review and residential infill fees.
Footings, a slab or crawlspace, and Portland's required stormwater management, usually drywells or planter boxes.
Tying the ADU into the main sewer. A basement or below-grade unit may need a sewage ejector pump to lift waste to the line.
The access path to the ADU, any required parking, and repairing the yard after the construction equipment leaves.
8 to 12 percent of total scope. For unknown soil, old or undersized utilities, and code surprises common on Portland infill lots.
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We wanted a detached ADU for my mother and got quotes that ranged wildly with no detail behind them. Woodland showed up with a real budget, a permit plan, and an honest answer about our sloped lot. Six months later there is a finished cottage in the backyard. It came in on the estimate, and the permitting they handled completely.
The single-PM thing is not marketing. We had one phone number from the permit application to the final inspection. They walked us through SDCs and utility connections up front, so there were no surprise line items halfway through.
We converted our old garage into a rental and it has paid for itself faster than we expected. The design made 500 square feet feel like a real home, and they reused the existing shell to keep the cost down.
Building an ADU in Portland costs $135,000 to $475,000 or more in 2026, depending on the type. A basement or garage conversion is the most cost-effective, often $135K to $180K, because it reuses an existing structure. A detached backyard ADU most commonly runs $280K to $360K (about $300 to $450 per square foot) since it is a new building with its own foundation, roof, utilities, kitchen, and bath. Larger high-end detached units reach $475K and up.
A basement or garage conversion is the cheapest path to a legal ADU because it reuses an existing structure instead of building a new foundation, roof, and shell. A basement conversion in Portland often starts around $135K and a garage conversion around $145K. A detached new ADU costs the most because it is ground-up construction, commonly $280K and up.
ADUs can trigger System Development Charges in Portland, but many qualify for exemptions or waivers depending on the size of the unit and any use restrictions. Because the fee schedule is updated annually and the rules change, confirm your specific SDCs with the city early in the process so they are in your budget from the start.
Portland generally allows a detached ADU up to 800 square feet by right, and up to 75 percent of the primary home or 1,000 square feet, whichever is smaller, with the required setbacks. Conversions of an existing garage or basement follow the footprint of the existing structure. Square footage, a second story, and stairs all add to the cost.
A garage or basement conversion typically takes about 3 to 4 months of construction. An attached ADU runs 4 to 5 months, and a detached new ADU usually takes 5 to 7 months after design and permitting. Permit timelines in Portland add a few months up front, so we start design and the permit application early so the build stays on schedule.
Yes. An ADU adds livable square footage, a potential rental income stream, and flexible space for family, all of which support resale value in Portland's housing market. Detached ADUs in particular are in high demand. The return is strongest when the ADU is well designed, permitted, and finished to match the main home.
Yes. An ADU requires building, electrical, plumbing, and mechanical permits, and a detached unit needs water, sewer, and electrical run from the house or street, sometimes with separate meters. As your design-build contractor, we handle the permits, plan review, and utility connections under one contract so nothing falls through the cracks. See our ADU builder process for how we run a project start to finish.
The estimates above reflect 2026 labor and material costs across the Portland metro. We design and build ADUs throughout these communities. Find your city for local project examples.
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