ADU Contractor Portland

Boss PDX is a licensed Portland, Oregon general contractor (CCB #232383, WA license BOSSPPL793RN) specializing in accessory dwelling units. We design and build every type of ADU — detached new construction, garage conversions, basement conversions, and attached additions — across Portland, Lake Oswego, West Linn, Tigard, Tualatin, and the surrounding metro. Free on-site scope and estimate, same-day reply, and a fixed written scope before any work starts.

What Is an Accessory Dwelling Unit (ADU)?

An accessory dwelling unit is a smaller, self-contained residence built on the same lot as an existing single-family home. Every ADU includes its own kitchen, bathroom, sleeping area, and private entrance, and is built to the same Oregon Residential Specialty Code as the primary house. In practice, an ADU is a fully independent living space that happens to share a tax lot with a larger home.

Portland is one of the most ADU-friendly cities in the country. Oregon Senate Bill 1051 (2017) required cities to allow at least one ADU on any lot zoned for single-family residential, and Portland went further — eliminating owner-occupancy requirements, dropping minimum lot size restrictions, and streamlining the permitting path. The Residential Infill Project (RIP) expanded options even more, allowing up to two ADUs on most single-family lots in R5 through R2.5 zones. If you own a residential lot in Portland, you almost certainly have the right to build an ADU on it.

Types of ADUs We Build in Portland

Detached New-Construction ADUs

A detached ADU is a standalone structure built from scratch in your backyard — sometimes called a backyard cottage or granny flat. This is the most flexible ADU type because you start with full control over layout, orientation, ceiling height, and finishes. Portland zoning allows detached ADUs up to 800 square feet or 75% of the primary dwelling's living area, whichever is less. Most detached ADUs we build range from 400 to 800 square feet and include one bedroom, a full kitchen, a full bathroom, a living area, and in-unit laundry.

Construction requires a new foundation (typically a concrete slab-on-grade or crawlspace), new framing and roofing, new utility connections for sewer, water, and electrical, and full mechanical systems — HVAC, plumbing, and electrical panels. The result is a completely independent structure that maximizes privacy for both the homeowner and the ADU occupant.

Garage Conversions

Converting an existing garage is often the fastest and most cost-effective path to an ADU because the foundation, framing, and roof already exist. Work focuses on insulation, weatherproofing, plumbing rough-in, electrical upgrades, HVAC installation, interior framing for kitchen and bath, and finish work — flooring, cabinetry, fixtures, and trim. Many Portland garages need structural upgrades and foundation reinforcement to meet residential occupancy code.

We run garage-to-ADU conversions as a dedicated service. Full detail on scope and sequencing is at our garage conversion page. One consideration: converting your garage means losing covered parking, which can affect daily routine and resale appeal. We help you weigh that trade-off during the initial consultation.

Basement Conversions

If your Portland home has a basement with adequate ceiling height (7 feet minimum for habitable space under code), a basement ADU can be an excellent option. The scope focuses on moisture mitigation, egress window or door installation, utility separation, insulation, interior framing, and finish work. A separate entrance is required — either an existing exterior door or a new one cut at grade on a sloped lot.

Basement ADU conversions share DNA with our broader basement finishing and remodeling work, but an ADU conversion adds a permitted kitchen, code-compliant egress, fire separation between units, separate utility metering, and independent heating and ventilation. We handle the full scope under one contract.

Attached Additions

An attached ADU is built as an addition to the existing home — a bump-out, second-story addition, or wing extension — with its own separate entrance. This works well on lots where setback requirements limit detached construction or where the homeowner wants a connected but independent living space for a family member. Our home additions and extensions team handles attached ADUs with the structural engineering, permitting, and construction process used for any major addition, plus the separate kitchen, bath, entrance, and utility connections required for a legal ADU.

Portland ADU Zoning and Regulations

Lot Coverage and Setbacks

Portland's R5 zones — where most ADUs are built — allow 45% maximum lot coverage, including all structures on the lot. Side and rear setbacks for a detached ADU are typically 5 feet, with reduced setbacks sometimes available for conversions of existing structures that are already closer to the property line. Height limits for detached ADUs are generally 20 feet in most residential zones. Corner lots, flag lots, and lots in overlay zones have additional rules — we verify your specific constraints before designing anything.

SB 1051 and Owner-Occupancy

Oregon Senate Bill 1051 required every city to allow at least one ADU on any single-family-zoned lot and prohibited cities from imposing parking requirements solely because of an ADU. Portland eliminated its owner-occupancy requirement as part of compliance — meaning you do not need to live on the property to build or rent an ADU. This opened the door for investor-owners and landlords to add ADUs to rental properties, not just owner-occupied homes.

SDC Waivers and Reductions

System Development Charges are one-time city fees for infrastructure — water, sewer, transportation, and parks. For a new ADU in Portland, SDCs can run $15,000 to $30,000 or more depending on unit size and current fee schedules. Portland has offered SDC waiver programs for ADUs at various points, most recently waiving SDCs entirely for ADUs under 800 square feet. Eligibility and terms change based on city council action and available funding, so confirm current status before you finalize your budget. We track these programs and advise you on what is available.

Utility Connection Requirements

Every ADU needs connections to water, sewer, and electrical service. A detached ADU typically requires a new sewer lateral connection to the city main, a water service tap or branch from the existing service, and a new or upgraded electrical panel with a dedicated meter. Conversions may tie into existing utilities with upgrades, depending on capacity. The Bureau of Environmental Services handles sewer permits, the Portland Water Bureau handles water, and electrical is coordinated with Portland General Electric (PGE) or Pacific Power. We manage all utility coordination as part of the project.

BDS Permitting Process for ADUs

Every ADU in Portland requires a building permit from the Bureau of Development Services (BDS). The process typically works as follows: first, a pre-application conference or zoning verification to confirm your lot qualifies and identify any overlay zones, easements, or environmental constraints. Second, preparation of construction drawings — architectural plans, structural engineering, mechanical plans, and a site plan showing setbacks, lot coverage, and utility routing. Third, submittal to BDS for plan review covering zoning, structural, energy, mechanical, plumbing, and electrical code compliance. Plan review typically takes 4 to 8 weeks, though timelines vary with BDS workload. Fourth, permit issuance, after which construction begins with BDS inspections at key stages — foundation, framing, rough-in, insulation, and final — before a certificate of occupancy is issued.

Boss PDX manages the entire permitting process: we prepare drawings, submit the application, respond to plan review corrections, schedule inspections, and coordinate with BDS through to final sign-off. We do not start framing on anything that is not permitted, and we do not guess at code — if a detail is unclear, we get it confirmed with the jurisdiction before it is built.

How Much Does an ADU Cost in Portland?

Cost depends on ADU type, size, site conditions, finish level, and utility complexity. Realistic ranges based on our experience building ADUs in the Portland metro:

• Detached new-construction ADU: $150,000 to $350,000+. A 400-square-foot studio cottage with standard finishes lands toward the lower end; an 800-square-foot one-bedroom with premium finishes and complex site work pushes higher.
• Garage conversion ADU: $80,000 to $200,000+. The existing structure reduces foundation and framing costs, but plumbing, electrical, HVAC, insulation, and finish work still add up — especially if the garage needs structural upgrades.
• Basement conversion ADU: $90,000 to $200,000+. Costs vary significantly with ceiling height, moisture conditions, egress requirements, and existing finish level.
• Attached addition ADU: $120,000 to $300,000+. Similar to a home addition plus a full kitchen, separate entrance, and utility separation.

These ranges include design, permitting, all construction labor and materials, and final inspections. We provide a fixed written estimate before you commit, and any change during construction goes through a written change order. Request a free estimate here.

ADU Construction Timeline

From first consultation to move-in, most ADU projects in Portland take 6 to 12 months:

• Design and engineering: 2 to 6 weeks, depending on complexity and how quickly decisions are made on layout and finishes.
• Permitting: 4 to 10 weeks for BDS plan review. Clean submittals move faster; projects in overlay zones or with unusual site conditions may require additional review cycles.
• Construction: 3 to 6 months for detached new builds, 2 to 4 months for garage or basement conversions. Weather, material lead times, and inspection scheduling all affect the construction window.

The biggest variable is usually permitting — BDS review times fluctuate with workload, and incomplete submittals can add weeks. We submit complete plans the first time to minimize back-and-forth and track your application so nothing stalls.

Rental Income and Return on Investment

A well-designed ADU in Portland can generate $1,200 to $2,500 or more per month in long-term rental income, depending on size, location, and finishes. Short-term rental (Airbnb, VRBO) rates can be higher, but Portland's short-term rental regulations require owner occupancy and a current city permit — rules that change periodically and should be verified before building a business plan around nightly rentals.

Beyond monthly cash flow, a permitted ADU typically adds $100,000 to $200,000 or more in appraised property value — often recovering a significant portion of construction cost at resale. The combination of rental income and property appreciation makes an ADU one of the strongest return-on-investment home improvements available to Portland homeowners.

Financing Your ADU

Most homeowners finance their ADU through a home equity line of credit (HELOC), a cash-out refinance, a construction-to-permanent loan, or an ADU-specific loan product — several lenders now underwrite based on projected rental income from the completed unit. We are not lenders and do not provide financial advice, but we can connect you with local lenders who specialize in ADU financing.

Our ADU Design and Build Process

1. Free on-site consultation. One licensed lead visits your property, walks the lot, and identifies constraints — setbacks, slope, utility access, tree canopy, neighbor considerations. No pressure, no sales pitch.
2. Design and fixed written scope. We develop plans, coordinate structural engineering, and prepare a detailed scope with a fixed price. You know what you are paying before you sign anything.
3. Permitting. We prepare construction drawings, submit to BDS, respond to comments, and track the application through to permit issuance.
4. Construction. Your lead carpenter and project manager are on the job throughout — one point of contact, consistent crew, no rotating subs you have never met. Any change goes through a written change order before we touch it.
5. Final walkthrough and inspection. We walk the completed ADU with you in person, address punch-list items, and coordinate the final BDS inspection for certificate of occupancy.

Why Hire Boss PDX as Your Portland ADU Contractor?

Six years building in Portland. A 4.9 out of 5 rating on Google across 60+ reviews. Licensed, bonded, and insured in both Oregon (CCB #232383) and Washington (BOSSPPL793RN). A bench of 41 named trade partners — structural engineers, mechanical contractors, framers, electricians, plumbers — so your project never stalls waiting on a sub we have never worked with. See the full list on our partners page.

We are not a volume builder cranking out identical prefab units. Every ADU is designed for the specific lot, the specific homeowner, and the specific use case — whether that is rental income, housing for an aging parent, a home office, or a guest suite. One lead carpenter, one project manager, and a fixed-scope contract that does not drift once work starts.

Frequently Asked Questions

How long does it take to build an ADU in Portland?

Most ADU projects take 6 to 12 months from initial consultation to move-in. Garage and basement conversions typically run 5 to 8 months because much of the structure already exists. Detached new construction runs 8 to 12 months due to foundation work, full framing, and more extensive utility connections. The single biggest variable is BDS plan review, which can take 4 to 10 weeks depending on workload and submittal quality.

Do I need to live on the property to build an ADU in Portland?

No. Portland eliminated its owner-occupancy requirement following Oregon Senate Bill 1051. You can build and rent an ADU on a property you own but do not live in, and you can rent both the primary house and the ADU to separate tenants. Short-term rental (Airbnb-style) has its own regulations that still require owner occupancy in most cases.

What permits do I need for an ADU in Portland?

At minimum, a building permit from BDS including plan review for zoning, structural, mechanical, plumbing, and electrical compliance. Depending on your project, you may also need a sewer connection permit from the Bureau of Environmental Services, a water service permit from the Portland Water Bureau, and electrical service coordination with PGE or Pacific Power. If your lot is in an environmental or historic overlay zone, additional land use review may be required. Boss PDX manages the entire permitting process on your behalf.

Can I build two ADUs on my Portland lot?

In many cases, yes. Portland's Residential Infill Project (RIP), which took effect in 2021, allows up to two ADUs on most single-family lots in R5 through R2.5 zones. Total lot coverage must stay within your zone's maximum, and not every lot qualifies — setbacks, lot size, and existing structures all factor in. We evaluate your lot's capacity during the initial consultation.

Are ADU System Development Charges still waived in Portland?

Portland has offered SDC waiver programs at various points over the past decade, saving homeowners $15,000 to $30,000 or more on a new ADU. Availability and terms change based on city council action and funding. We track these programs closely and will advise you on current eligibility when you start your project.

Will an ADU increase my property taxes?

Yes. Adding a permitted ADU increases your assessed property value and therefore your property taxes — typically $1,500 to $4,000 per year for a standard ADU, though this varies with size, construction cost, and Multnomah County's assessment. The rental income from the ADU typically exceeds the tax increase many times over, making the net financial impact strongly positive for most homeowners.

Ready to Build Your Portland ADU?

Whether you are converting a garage, finishing a basement, or building a detached cottage from the ground up, Boss PDX has the experience, the trade network, and the fixed-scope process to get it done right. Call 844-BOSS-PDX (844-267-7739) or request a free estimate online. One licensed lead, one call, straight answers.