Common ADU Design Mistakes (and How to Avoid Them)

Accessory Dwelling Units (ADUs) have exploded in popularity across Central Oregon — and for good reason. Whether you’re a Bend homeowner looking to generate rental income, build a guest suite, or create multigenerational housing, an ADU can dramatically boost both your property value and livability.

But as more homeowners rush to build, many overlook key design details that can make or break their investment. From poor layouts to costly permitting mistakes, even small missteps can lead to major frustration — or wasted money.

Here’s a guide to the most common ADU design mistakes we see in Bend and Deschutes County — and how you can avoid them to ensure your project adds lasting value.

Mistake #1: Ignoring Local ADU Regulations Early

Before you start sketching layouts or hiring a contractor, it’s crucial to understand your city or county’s ADU rules.

In Bend, for example, there are clear guidelines for setbacks, height limits, and parking requirements. In Deschutes County, rural ADUs face stricter wildfire safety and septic capacity standards.

✅ How to Avoid It

• Meet with the City of Bend Planning Division or Deschutes County Community Development before you design.

• Confirm key details like maximum square footage, lot coverage, and height limits.

• Make sure your ADU plan fits within your property’s zoning designation and any HOA rules.

Ignoring this step can lead to costly redesigns — or worse, permit denials.

Mistake #2: Designing Without the End Use in Mind

One of the biggest traps homeowners fall into is not defining how they plan to use the ADU.

Is it for rental income, aging parents, or a home office? Each purpose comes with different design needs.

✅ How to Avoid It

• For rental ADUs, prioritize privacy — separate entrances, soundproofing, and a compact but efficient layout.

• For family use, think accessibility — single-level designs, wider doors, and step-free showers.

• For flex space, include multipurpose layouts (think Murphy beds or convertible rooms).

Knowing your end goal early helps you design smart and avoid costly mid-project changes.

Mistake #3: Skimping on Natural Light and Ventilation

ADUs are smaller than main homes, so light and air play a huge role in making the space feel livable. Too many designs rely on minimal windows or poor orientation, making interiors feel dark or cramped.

✅ How to Avoid It

• Position windows to capture morning or afternoon light.

• Add skylights or solar tubes to brighten interior spaces.

• Use open layouts and light-colored finishes to create a sense of space.

• Consider cross-ventilation to keep the ADU cool in Bend’s dry summers.

A bright, airy ADU feels more inviting — and will rent or resell more easily.

Mistake #4: Overcomplicating the Floor Plan

A well-designed ADU doesn’t need to be large to feel functional. Overcomplicated layouts waste precious square footage and drive up costs.

✅ How to Avoid It

• Keep plumbing close together (bathroom and kitchen on the same wall).

• Use built-in storage instead of bulky furniture.

• Eliminate unnecessary hallways — open-concept spaces work best.

• Opt for multi-functional zones, like a kitchen island that doubles as a dining area.

Simplicity equals affordability — and better livability.

Mistake #5: Forgetting Privacy Between Units

Many Central Oregon homeowners forget that privacy goes both ways — for the main house and the ADU. Without proper planning, shared driveways, visible patios, or window placement can create awkward living situations.

✅ How to Avoid It

• Stagger entrances so neither faces directly into the other.

• Use landscaping or fencing to define boundaries.

• Consider sound insulation between shared walls or garages.

Thoughtful separation makes both spaces more comfortable — and more attractive to renters.

Mistake #6: Underestimating the Budget

ADU construction costs in Central Oregon typically range from $175,000 to $300,000 depending on size, finishes, and site conditions. Many owners underestimate expenses for utilities, permits, or impact fees.

✅ How to Avoid It

• Get detailed estimates from multiple contractors.

• Ask about permit fees, utility hookups, and site prep costs.

• Add a 10–15% contingency for unexpected expenses.

• Explore financing options like HELOCs, ADU-specific loans, or state grants (see: How to Finance an ADU in 2025).

A clear budget helps you stay on track — and prevents project delays.

Mistake #7: Neglecting Energy Efficiency

With Bend’s focus on sustainability, energy-efficient ADUs aren’t just good for the planet — they lower long-term costs and boost resale value.

✅ How to Avoid It

• Choose Energy Star-rated appliances and LED lighting.

• Add extra insulation for both comfort and savings.

• Consider solar panels or battery-ready wiring for future upgrades.

• Use high-efficiency mini-split systems for heating and cooling.

Many energy upgrades also qualify for Oregon or federal tax incentives, helping offset upfront costs.

Mistake #8: Forgetting the Exterior Design

Even if your ADU is behind the main house, curb appeal still matters. A mismatched or generic design can hurt your property’s overall aesthetic and resale value.

✅ How to Avoid It

• Match your ADU’s roofline, colors, and materials to the main house.

• Use landscaping to blend the unit naturally into the lot.

• Consider outdoor features like small patios or decks for added livability.

In neighborhoods like NW Crossing or Old Bend, a cohesive design adds both charm and value.

Designing an ADU in Central Oregon offers incredible flexibility — but it’s also a complex process that rewards careful planning.

By understanding local rules, defining your ADU’s purpose, and prioritizing smart, efficient design, you can create a space that enhances both your lifestyle and your investment.

Avoiding these common design mistakes ensures your ADU project doesn’t just add square footage — it adds real, lasting value.

FAQs

Q: What’s the ideal size for an ADU in Bend?

A: Most ADUs in Bend range from 400 to 800 square feet, though the city allows up to 800 sq ft (or more in some cases). Always verify with city planning before finalizing plans.

Q: Can I use prefab or modular ADUs in Bend or Deschutes County?

A: Yes! Prefab units are increasingly popular for their efficiency — just make sure the design complies with local building and wildfire codes.

Q: Should my ADU have separate utilities?

A: Separate meters can simplify billing for rentals but add upfront cost. For family use, shared utilities may be more practical.

Q: Does an ADU increase property taxes?

A: Yes, adding an ADU generally increases your property’s assessed value — but it also boosts resale and rental potential significantly.