Accessory Dwelling Units — or ADUs — are growing in popularity across the Pacific Northwest. Whether it’s a detached backyard cottage, a converted garage, or a basement apartment, ADUs offer homeowners a flexible and valuable way to add space, income potential, or multi-generational housing to their property.
At Hardline Design and Construction, we help homeowners navigate the design, permitting, and construction process for custom-built ADUs that add long-term value to their homes. If you’re considering building one, here’s what you need to know before you get started.
What is an ADU?
An Accessory Dwelling Unit (ADU) is a smaller, self-contained living space located on the same lot as a primary residence. It has its own kitchen, bathroom, entrance, and often laundry facilities. ADUs can take many forms, including:
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Detached new construction (standalone backyard units)
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Garage conversions
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Basement apartments or lower-level conversions
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Above-garage suites or additions
ADUs are commonly used for rental income, guest housing, home offices, or private living space for aging parents or adult children.
Benefits of Building an ADU
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Extra Income – Long-term or short-term rental opportunities can help offset mortgage costs.
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More Space – Perfect for guests, remote work, creative studios, or independent living.
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Multi-Generational Living – Offer privacy and independence for family members while staying close.
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Increased Property Value – A well-built ADU can significantly boost resale value.
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Flexible Use – Today’s ADU can be a rental, but tomorrow it might be a home office or guest suite.
What to Know Before You Build
1. Zoning and Local Regulations
Zoning codes vary by city and neighborhood. Many cities in Oregon and Washington have relaxed their rules to encourage ADU development, but you still need to review:
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Lot size minimums
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Height limits and setbacks
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Maximum square footage
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Parking requirements
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Owner-occupancy rules
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Utility connection policies
Tip: Hardline can help you review and interpret your local ordinances before you begin designing your unit.
2. Permitting Process
ADUs typically require building permits, and sometimes planning review or land use approval. The permit process can take several weeks, depending on your location.
Our team manages this for you — from submitting permit applications to coordinating with inspectors — to ensure your project stays on track.
3. Budgeting and Financing
Costs for ADUs vary based on size, design, materials, and site conditions. A detached ADU in the Portland area, for example, might range from $120,000 to $300,000+, depending on the level of finish.
Consider your financing options, such as:
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Home equity loans or HELOCs
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Construction loans
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Cash-out refinancing
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Local ADU incentive programs or grants
4. Design and Layout
Functionality is key in ADU design. You’ll want to make the most of limited space by incorporating:
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Efficient layouts with open living areas
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Built-in storage and multi-use furniture
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Natural light through strategic window placement
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Private entryways for tenant or guest independence
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Soundproofing if attached to the main home
At Hardline, we work with you to design an ADU that balances livability, code requirements, and your property’s footprint.
5. Construction and Timeline
The construction timeline depends on project scope and permitting speed, but most ADUs take 4 to 8 months from design to completion.
We handle the entire process — excavation, foundation, framing, mechanicals, finishes, and final inspection — with regular updates and clear communication throughout the build.
Why Build Your ADU with Hardline Design and Construction?
We’ve helped homeowners across the region plan and build ADUs that fit their needs, budget, and lifestyle. Our team brings decades of residential construction experience, along with a deep understanding of local codes and a commitment to quality craftsmanship.
When you choose Hardline, you get:
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End-to-end project management
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Transparent pricing and realistic timelines
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Custom design tailored to your property
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Hands-on experience with city permitting
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A team that cares about your vision and investment
Let’s Bring Your ADU Project to Life
If you’re ready to add space, income, or flexibility to your property with an ADU, we’d love to help. Contact Hardline Design and Construction today to schedule a consultation and learn what’s possible for your home.