Maximizing Your ADU Space: How to Calculate Usable Area

Accessory Dwelling Units (ADUs) have become a popular way to add value to properties and create additional living spaces in places like Bend, Oregon. However, one of the most critical aspects of designing and building an ADU is understanding how to maximize its usable space. Whether you plan to use your ADU as a rental, guest house, or personal retreat, knowing how to calculate usable area can ensure your investment pays off. This guide will walk you through the key considerations and how to apply the rules specific to Deschutes County, based on their Research Checklist for ADUs.

Why Maximizing Usable Space Matters

Every square foot counts in an ADU. The way you design and calculate your space can directly impact the functionality and comfort of your unit. By maximizing usable area, you can:

• Increase Functionality: Ensure there’s enough room for daily living activities like cooking, sleeping, and entertaining.
• Boost Property Value: A well-utilized ADU often attracts higher rents or resale value.
• Meet Legal Requirements: Compliance with local building codes and regulations is non-negotiable. Calculating usable space accurately helps avoid costly redesigns.

Understanding Usable Space vs. Gross Floor Area

One of the first steps in maximizing your ADU’s space is understanding the distinction between usable space and gross floor area:

• Gross Floor Area: This includes the total square footage of all floors, measured from the exterior walls.
• Usable Space: The area available for living purposes, excluding spaces like wall thickness, utility closets, or areas with low ceilings (less than 7 feet in height).

The Deschutes County ADU guidelines specify maximum size limits based on gross floor area. For example:

• Detached ADUs are limited to 900 square feet.
• Attached ADUs may also have limitations depending on the property’s zoning and structure.

Step-by-Step Guide to Calculating Usable Area

1. Start with the Total Area Measure the gross floor area of the planned ADU. Include all levels if you’re building a multi-story unit. For detached units, this is typically the footprint of the structure.
2. Account for Ceiling Heights Usable space excludes areas with ceiling heights under 7 feet, as per building codes. If you’re converting an attic or basement, measure carefully to ensure compliance.
3. Exclude Non-Livable Spaces Deduct areas dedicated to mechanical systems, staircases, or exterior walls. For example, utility closets housing HVAC systems or water heaters should not be included in your calculation of usable living space.
4. Factor in Egress Requirements Bedrooms and other habitable rooms must meet specific egress standards (like window size and placement) to qualify as usable space. Review these rules to avoid disqualifying certain areas.
5. Plan for Shared Spaces If your ADU shares access points or facilities (e.g., a laundry room) with the primary residence, you’ll need to determine how these are calculated within your zoning code’s parameters.

Design Strategies to Maximize Usable Space

Maximizing space isn’t just about compliance; it’s also about smart design. Here are some tips:

1. Go Vertical

If your property’s zoning allows it, consider a two-story design for detached ADUs. A vertical layout helps maximize square footage without increasing the footprint, leaving more outdoor space available.

2. Use Multi-Functional Furniture

Built-in furniture like Murphy beds, foldable tables, and storage benches can dramatically enhance functionality while saving space.

3. Open Floor Plans

Eliminating non-essential walls can make small spaces feel larger. Combine kitchen, dining, and living areas into one open space to maximize usability.

4. Maximize Storage

Utilize vertical storage solutions, like floor-to-ceiling cabinets or shelving, to free up floor space. Don’t forget to use underutilized areas, such as under the stairs or overhead loft spaces.

5. Natural Light

Incorporate large windows and skylights to make the space feel more open and inviting. Good lighting can improve the perception of space, even in smaller ADUs.

Key Deschutes County Considerations

Deschutes County has specific rules and guidelines for ADUs, and understanding these will help you make the most of your project. Some critical points include:

• Maximum Size: Detached ADUs must not exceed 900 square feet.
• Setbacks and Lot Coverage: ADUs must comply with property setbacks and lot coverage requirements, which may limit the overall footprint.
• Parking Requirements: Depending on your zoning, additional parking may be required for the ADU, impacting your design and available space.
• Utilities: Ensure your ADU’s mechanical systems are compact and efficient to save space while meeting utility requirements.

Practical Example: Maximizing Space in a 900-Square-Foot ADU

Let’s say you’re building a detached ADU in Bend, Oregon, with a maximum allowable size of 900 square feet:

• Divide into Zones: Dedicate approximately 300 square feet to a combined kitchen and living area, 200 square feet for a bedroom, 100 square feet for a bathroom, and the remaining 300 square feet for a second bedroom or office.
• Optimize Circulation: Use pocket doors instead of swinging doors to save space and ensure hallways are minimal but functional.
• Incorporate Outdoor Space: A small patio or deck can extend the living area without adding to the gross floor area.

Conclusion

Maximizing your ADU space starts with understanding how to calculate usable area accurately. By leveraging smart design strategies and adhering to Deschutes County’s guidelines, you can create a functional, compliant, and comfortable ADU that meets your needs and enhances your property value. For more information, consult the Deschutes County ADU Research Checklist and consider working with professionals familiar with local requirements to make your ADU project a success.