ADU & Addition Design

in Santa Rosa & Sonoma County

Whether you're adding a detached accessory dwelling unit, expanding your primary home, or reimagining an underused space, an addition is one of the biggest investments you'll make in your property. At Humanity Design Works, we handle the full scope of ADU and addition projects, from structural design and permit drawings through interior design and material selection, so every phase of the project reflects one cohesive vision.

What We Design

  • ADU design, from initial concept through permit-ready construction drawings

  • Home additions, including room expansions, second-story additions, and structural reconfigurations

  • Interior design and space planning for the new space, integrated with your existing home

  • Material and finish selection, coordinated with your home's overall style

  • Permit-ready drawings prepared to meet your local jurisdiction's requirements

Our Process

  1. Initial consultation. We walk the property, discuss your goals for the new space, and assess what's structurally and practically possible.

  2. Concept and structural planning. We develop the layout and structural approach, balancing your vision with buildability and budget.

  3. Design development. Interior design, material selection, and finish choices are developed alongside the structural plans, not as an afterthought.

  4. Permit-ready drawings. Final drawings are prepared to meet the requirements of your local jurisdiction.

  5. Collaboration through construction. We stay involved throughout the build, working with your contractor to keep the finished space aligned with the original design.

Why Homeowners Choose HDW

An addition or ADU touches both the structure of your home and how you'll actually live in it. Because we handle both the architectural and interior design sides of the project ourselves, your new space is designed as a whole from day one, not stitched together from separate structural and design decisions made in isolation. That means a space that fits your home structurally and feels like it was always meant to be there.

Ready to Start Your ADU or Addition?

If you're planning an ADU, addition, or expansion in Sonoma, Marin, or Napa County, we'd love to talk through your project. Schedule a Consultation to get started.