Garage Conversion vs. New ADU in Portland: Costs & Benefits
Which ADU Project Is Right for Your Portland Property?
When considering an Accessory Dwelling Unit (ADU) in Portland, homeowners typically face a crucial decision: converting an existing garage or opting for a completely new, standalone ADU. Each option carries unique benefits, drawbacks, and costs. Carefully evaluating these factors will help you choose the solution that best suits your property and goals.
Garage ADU Conversions
Benefits of Converting Your Garage Into an ADU
Lower Cost Compared to New Construction
Garage conversions typically offer significant cost savings compared to new builds. Because you’re leveraging existing structural elements—such as framing, foundation, and roofing—the construction expenses related to site preparation and foundational work can be substantially reduced. This makes garage conversions an attractive option for homeowners on tighter budgets.
Preserve Outdoor Living Space
By repurposing existing garage structures, you maintain valuable outdoor space. For properties with limited yard space or homeowners who prefer preserving landscaping, gardens, or outdoor recreational areas, a garage conversion ensures minimal disruption to the property's layout and usable outdoor area.
Drawbacks of Garage Conversion ADUs
Structural Limitations
Garages often require substantial upgrades to be legally converted into livable space. These upgrades might include reinforcing the foundation, adding vapor barriers, upgrading or replacing the roof, and installing insulation, heating, ventilation, and natural light solutions. Without these changes, the space won’t meet residential codes.
Design Constraints
You’re limited by the original structure’s footprint and ceiling height. This may constrain your desired layout or limit your ability to include modern features such as vaulted ceilings or expansive windows.
Loss of Storage or Parking
While converting a garage can be a smart space optimization strategy, it also means giving up enclosed storage or covered parking, which may affect resale value depending on your neighborhood.
Average ADU Garage Conversion Costs in Portland
Total Cost: $100,000 to $200,000
Cost per Square Foot: $150–$250, depending on upgrades, finishes, and complexity
New Build ADUs
Benefits of Building a New Detached ADU in Portland
Full Customization & Modern Design
Building a new ADU from the ground up offers unparalleled design flexibility. Homeowners can personalize every aspect—from layout and room configurations to window placements, ceiling heights, and architectural style. This complete control allows for thoughtful incorporation of energy-efficient features, natural lighting, accessibility considerations, and design cohesion with your existing home.
Long-Term Property Value & Rental Potential
New, detached ADUs tend to be perceived as more attractive, private, and functional by buyers and renters. These structures often command higher rental income and can add significant value to the property, especially when built to match or complement the main residence.
Drawbacks of New Build ADUs
Higher Construction & Permit Costs
Constructing a new ADU involves extensive costs beyond basic framing. These include site preparation (grading, excavation, foundation), utility hookups (sewer, water, power), and permitting fees. In some cases, build costs may approach or exceed $350,000 depending on scope and design complexity.
Yard Space Trade-Offs
Detached ADU housing requires a designated footprint, which can reduce available green space for pets, kids, gardens, or outdoor entertaining—an important consideration for homes with smaller lots in Portland’s urban neighborhoods.
Average New Build ADU Costs in Portland
Total Cost: $200,000 to $350,000+
Cost per Square Foot: $250–$400 based on size, layout, materials, and finish level
Other Key Factors for Portland Homeowners to Consider
Energy Efficiency
New ADUs offer an opportunity to integrate high-performance building materials, passive heating/cooling, solar panels, and advanced insulation. These upgrades can be more difficult and costly to retrofit in an older garage.
Timeline & Permitting Speed
Garage conversions are generally faster to complete, with shorter design, engineering, and permitting timelines. If you’re aiming for rental income or family housing in the near term, conversions are often the faster path to completion.
ADU Demand in Portland
ADUs are increasingly valuable in Portland. Whether you choose a conversion or a new build, you’ll be tapping into one of the city’s most in-demand home improvements. For more in-depth guidance on zoning and permitting, read our full Portland ADU Guide.
Internal Resources to Help You Plan Your ADU Project
Portland Remodeling Services – Learn how we help local homeowners add space and value
About Amplified Renovations – Meet the team behind your dream project
Kitchen Remodeling Services – Integrate a kitchen renovation into your ADU plans
Final Thoughts: Garage Conversion or New Build?
Choosing between a garage conversion and a new detached ADU depends on your budget, lot layout, and long-term goals. If you’re looking for cost savings and a quicker turnaround, garage conversions are a smart solution. But if you value complete design control and long-term equity, new builds are hard to beat.
Ready to Build Your ADU in Portland?
If you're looking for an ADU builder near you who understands the nuances of Portland zoning, permitting, and construction, Amplified Renovations is your trusted local partner. Our design-build team can help you explore both garage conversion and new build options that align with your goals.
Contact us today to schedule a free consultation and get started on your ADU project.
