Portland ADU Builders — Design-Build Accessory Dwelling Units
Crestwood Property Services designs and builds accessory dwelling units across Portland and the metro area, handling every step in-house from concept sketches through final occupancy permit. Planning a detached backyard cottage, converting a garage, or finishing a basement into a separate unit? Our owner-led crew delivers a home you can rent, live in, or move family into, built on a fixed price with no surprise allowances. With 15+ years of Portland remodeling experience and a workmanship warranty that stands behind every project, a complex build gets a lot simpler.
What Is an ADU?
An accessory dwelling unit (ADU) is a fully self-contained second home built on the same lot as a primary residence. Portland zoning allows ADUs on most residential lots, and an ADU can be detached from the main house, attached to it, or converted from existing space like a garage, basement, or attic. ADUs go by many names: granny flats, in-law suites, backyard cottages, casitas, mother-in-law apartments. The building code requirements are the same regardless of label — a private entrance, kitchen, bathroom, and sleeping area.
Portland has been one of the country's most ADU-friendly cities since the 1980s, and recent zoning updates have continued to loosen restrictions on size, setbacks, and parking. That makes it easier than ever to add square footage that earns rental income, houses an aging parent, gives an adult child their own space, or serves as a guest suite, home office, or studio. Done right, an ADU adds substantial resale value in Portland's tight housing market, often returning a meaningful portion of the build cost in appraised equity alone.
Why Build an ADU in Portland?
Portland homeowners build ADUs for very different reasons, and the way an ADU is designed should follow the way you plan to use it. Most of our clients fall into one of these patterns.
Rental Income
A well-designed 600-800 square foot ADU in Portland can earn anywhere from $1,500 to $2,500+ per month in long-term rent depending on neighborhood, finish level, and unit size. Short-term rentals are restricted by city rules, so we typically design for long-term tenants: separate utilities, soundproofed walls, and a layout that's livable year-round.
Aging in Place
Building a single-level ADU on your property lets aging parents stay close without giving up independence, and lets you sell the family home later without forcing a move. We design accessibility features in from the start: zero-step entries, wide doorways, curbless showers, lever hardware, and reinforced walls for future grab bars.
Multigenerational Living
Adult children moving back to Portland, returning siblings, or extended family relocating to be near grandkids all benefit from a separate, fully functional living space that maintains everyone's privacy.
Home Office, Studio & Guest Space
Remote work, creative practices, and hosting visitors all justify dedicated space outside the main house. An ADU built for these uses can still convert to a rental or in-law unit later, protecting your investment over the long run.
Long-Term Flexibility
The single best argument for an ADU is that its use can change with your life. Today's guest suite becomes tomorrow's rental, which becomes the next decade's caretaker apartment. An ADU is a 30-year asset, not a single-purpose addition.
Types of ADUs We Build in Portland
Every Portland lot has constraints: setbacks, tree canopy, slope, access, existing utility runs. The right type of ADU depends on what your property allows and how you plan to use the space. Crestwood builds all four common ADU configurations.
Detached ADUs (Backyard Cottages)
A standalone structure in the backyard, fully separate from the main house. Detached units offer the most privacy for both households, the most flexibility in design, and typically the strongest rental appeal. They're the most involved build of the four types because they require new foundation, framing, roof, and full utility runs; they also offer the highest long-term value. Portland code allows detached ADUs up to 800 square feet (or 75% of the main house, whichever is less) on most residential lots.
Garage Conversion ADUs
Converting an existing detached or attached garage into a living unit is often the fastest and least expensive way to add an ADU. You're starting with foundation, walls, and a roof already in place. The work goes into insulation, weatherization, code-compliant ceiling heights, plumbing, electrical, and a kitchen and bathroom. If your garage has the right dimensions and is in good structural shape, this can be the smartest path to an income-producing unit.
Basement ADUs
Older Portland homes (Craftsman bungalows, foursquares, mid-century ranches) often have unfinished basements that can be turned into a fully separate apartment with its own exterior entrance. The biggest design challenges are egress windows (required for legal bedrooms), ceiling height (Portland code requires 7 feet minimum for habitable space), moisture control, and creating a layout that doesn't feel like a basement. When the existing structure allows it, a basement ADU is usually the most cost-effective option for a homeowner who already has the square footage.
Attached ADUs & Internal Conversions
Carving a separate dwelling unit out of part of the main house: typically a wing, an upstairs unit with a separate entrance, or an addition that shares a wall with the existing home. Attached units share some structural and mechanical systems with the main house, which can reduce costs, but they require careful sound separation, fire-rated assemblies, and clear demising lines for code compliance.
Not sure which type fits your lot? That's what the free consultation is for. We'll walk your property, review zoning and setbacks, and tell you honestly what your options are before you spend a dollar on design.
Our Design-Build ADU Process
Most ADU projects involve a separate architect, separate contractor, and separate project manager. Three teams pointing fingers when something goes sideways. Crestwood is a design-build firm, which means one team owns the project from sketch to final walkthrough.
We come to your property, look at the lot, talk through how you want to use the ADU, and discuss zoning, setbacks, utility access, and rough budget. You leave the conversation with a realistic sense of what's possible. No pressure, no commitment.
Once you decide to move forward, we produce a concept design and preliminary site plan, confirm what Portland zoning allows, and identify any flags (sewer lateral, tree preservation, ROW improvements) that affect cost or timeline. You see a real plan before you commit to construction.
This is where Crestwood is different from most builders: we deliver a fixed-price proposal with no allowances, no "TBD" line items, no end-of-project surprises. You know what the ADU costs before we break ground. Design refinements happen here so the final drawings match your budget exactly.
Portland's ADU permit process involves zoning review, building plan review, and trade permits for plumbing, electrical, and mechanical work. We handle the entire submittal and any correction cycles. Typical permitting time in Portland runs 2-4 months depending on lot complexity and current city backlog.
Our in-house crew handles framing, exterior, mechanical rough-ins, insulation, drywall, finishes, and final trades. No subcontractors rotating through your backyard. The owner is on site regularly, not occasionally; we structure projects that way on purpose. Typical detached ADU construction runs 6-9 months from groundbreaking to final inspection.
Once Portland issues the certificate of occupancy, we do a punch-list walkthrough with you and address anything that didn't meet the standard. Our workmanship warranty starts the day you get the keys.
Typical Timeline: Detached ADU — 12-18 months from consultation to occupancy | Garage or basement conversion — 6-12 months
Why Crestwood for Your Portland ADU
Choosing an ADU builder in Portland means choosing a company that will be in your backyard for a year or more. The fit matters.
Owner on Every Project
The owner of Crestwood is on-site regularly throughout construction, not just at kickoff and final walkthrough. That's direct accountability, direct communication, and a personal stake in how your ADU turns out.
No Subcontractors
Our in-house crew handles framing, finishes, and most trade work directly. You're not coordinating with five different companies; you're working with one team that knows your project from day one.
Fixed Pricing, No Allowances
Most ADU builders quote with allowances for finishes, fixtures, and selections, and the actual cost lands well above the original number. Crestwood gives you a fixed price with all selections finalized before construction. The number we quote is the number you pay.
Workmanship Warranty Above Industry Standard
We stand behind every project with a warranty that lasts longer and covers more than most Portland builders offer. If something we built isn't right, we come back and fix it.
Portland Home Expertise
ADUs in Portland mean working around Craftsman bungalows, mid-century ranches, foursquares, and the quirks every older Portland home has: undersized service panels, narrow lots, mature trees, complicated setbacks. We've spent 15+ years on these houses and know how to integrate a new ADU without compromising the main home's character.
Design-Build Means One Team
When something changes mid-project (and on a complex build, something always changes), there's no architect blaming the builder or the builder blaming the architect. One team owns the outcome.
ADU Costs in Portland — What to Expect
ADU costs in Portland vary widely based on type, size, finish level, site complexity, and current material pricing. These ranges reflect what Portland homeowners are spending today on a fully permitted, code-compliant unit. Every Crestwood project gets a fixed-price proposal; these ranges exist for planning, not for quoting.
Garage Conversion ADU
$150,000 - $275,000
Conversions are usually the most affordable route because the existing structure provides foundation, walls, and roof. Range varies based on existing garage condition, whether utility upgrades are needed, and finish level.
Basement ADU
$175,000 - $325,000
Cost depends heavily on whether ceiling heights, egress windows, and waterproofing are already in good shape. Older Portland basements often need significant work before they can be permitted as habitable space.
Detached ADU (Backyard Cottage)
$350,000 - $600,000+
Detached units require new foundation, full framing, roof, exterior cladding, and complete utility runs (sewer, water, gas, electrical). Pricing scales with square footage, finish level, and site work (tree removal, grading, sidewalk requirements).
Attached ADU
$200,000 - $400,000
Internal conversions and additions vary the most because every house is different. Cost depends on how much new construction is involved versus reusing existing space.
Site costs (sewer connections, system development charges, tree mitigation, ROW improvements) typically add $20,000 to $60,000 on top of the base build cost. Portland waives some SDCs for ADUs, but utility connection fees and permit costs still apply. We itemize all of this in your fixed-price proposal so you see the full picture before you commit.
Portland Neighborhoods We Serve
Crestwood builds ADUs throughout Portland and the surrounding metro. Each Portland neighborhood has its own zoning quirks: historic overlays, tree canopy requirements, setback rules, lot coverage limits. We work with these constraints every day and can tell you what's buildable on your specific lot during the free consultation.
Portland Neighborhoods
- Alberta & Alberta Arts
- Irvington & Alameda
- Laurelhurst & Beaumont-Wilshire
- Hawthorne & Division
- Sellwood & Westmoreland
- Eastmoreland & Woodstock
- St. Johns & Kenton
- Hillsdale & Multnomah Village
- Pearl District & Downtown
Surrounding Communities
- Beaverton
- Tigard
- Lake Oswego
- West Linn
- Tualatin
- Hillsboro
- Gresham
- Milwaukie
- Oregon City
- Sherwood
Frequently Asked Questions
How much does it cost to build an ADU in Portland?
Most Portland ADUs land between $150,000 and $600,000+ depending on type and size. Garage conversions are typically the most affordable at $150,000-$275,000, while a fully detached 700-square-foot backyard cottage with mid-range finishes generally runs $400,000-$500,000. Site costs (sewer, SDCs, tree mitigation) add another $20,000-$60,000. Crestwood quotes every ADU at a fixed price with no allowances, so the number you see is the number you pay.
How long does it take to build an ADU in Portland?
A detached ADU typically takes 12-18 months from initial consultation to final certificate of occupancy: 2-4 months for design and preliminary work, 2-4 months for permitting, and 6-9 months for construction. Garage and basement conversions usually run 6-12 months because permitting is simpler and construction is faster.
Do I need permits for an ADU in Portland?
Yes. Every ADU in Portland requires a building permit, and depending on the work involved, separate plumbing, electrical, and mechanical permits. New detached units also require zoning review. Crestwood handles the entire permit submittal and correction cycle as part of the build.
Can I rent out my Portland ADU?
Yes, for long-term tenants. Portland allows long-term rentals (30+ day stays) in ADUs as a matter of right. Short-term rentals (Airbnb-style, under 30 days) require an Accessory Short-Term Rental permit and are restricted to your primary residence, so you generally cannot operate an ADU as a full-time short-term rental.
How big can an ADU be in Portland?
Detached ADUs can be up to 800 square feet or 75% of the floor area of the primary house, whichever is less. Internal and attached conversions follow different size rules based on the configuration. We confirm the maximum buildable size for your specific lot during the consultation.
Does an ADU increase my property value?
Generally yes. A well-built ADU typically returns a meaningful portion of its build cost in appraised equity, plus ongoing rental income if you choose to rent. The exact valuation impact depends on neighborhood, ADU size, and finish level. Portland's tight housing market tends to reward ADUs more than markets where housing is plentiful.
Will an ADU affect my property taxes?
Yes. Portland reassesses your property after an ADU is added, so your property taxes will increase to reflect the added value. The increase is typically modest relative to the rental income most ADUs generate, but plan for it in your numbers.
Do you handle ADU design, or do I need to hire an architect separately?
Crestwood is a full design-build firm. We handle architectural design, engineering coordination, and construction under one roof. You don't need a separate architect. This is one of the main reasons clients choose us: one team, one accountability point, one contract.
Can I live in the main house while you build the ADU?
Yes. For detached and garage-conversion ADUs, the work happens outside the main living space. There's noise and activity in the yard, but the main house stays fully functional. Basement and attached ADUs involve more shared space, and we coordinate the schedule with you so disruption is contained.
Ready to Plan Your Portland ADU?
Schedule a free, no-pressure consultation. We'll come to your property, look at what's buildable, and give you a clear picture of cost, timeline, and what type of ADU fits your goals. No deposit, no commitment. Just a real conversation with a Portland builder who's done this 100+ times.
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