ADU & DADU Specialists
Add Value to Your Property
With KOI Build Co
Accessory Dwelling Units (ADU) and Detached ADUs (DADU). Maximize your property value with versatile additional living spaces.
ADU & DADU Builders in Olympia, Lacey, Tumwater & South Puget Sound WA
KOI Build Co designs and builds ADUs and DADUs (detached accessory dwelling units) in Olympia, Lacey, Tumwater and communities across South Puget Sound, WA. These flexible living spaces can serve as rental units, guest suites, home offices or housing for family members.
We guide you through local zoning, permitting and design requirements so your accessory dwelling unit fits your property, budget and long-term goals. Our design-build approach streamlines the process, coordinating plans, utilities, foundations, framing, finishes and inspections under one roof.
Whether you are adding an attached ADU, converting existing space or building a stand-alone backyard cottage, KOI Build Co delivers efficient, well-planned accessory units that add value and versatility to your property.
Why Choose Us
Olympia's Trusted ADU & DADU Builders
With over 20 years of experience, KOI Build Co has become the go-to ADU contractor for homeowners across South Puget Sound. We specialize in creating additional living spaces that maximize property value.
Our Work
Featured Projects
Real results from homeowners who trusted us.
Olympia, WA
Detached DADU
600 sq ft detached ADU with kitchen and bathroom.
Olympia, WA
Detached DADU
600 sq ft detached ADU with kitchen and bathroom.
Lacey, WA
Garage Conversion
Converted attached garage into 1-bedroom living space.
Lacey, WA
Garage Conversion
Converted attached garage into 1-bedroom living space.
Tumwater, WA
Basement ADU
Finished basement with separate entrance and kitchenette.
Tumwater, WA
Basement ADU
Finished basement with separate entrance and kitchenette.
Olympia, WA
Over-Garage ADU
ADU built above existing garage with private stairs.
Olympia, WA
Over-Garage ADU
ADU built above existing garage with private stairs.
Lacey, WA
Backyard Cottage
Charming backyard cottage with private patio.
Lacey, WA
Backyard Cottage
Charming backyard cottage with private patio.
Olympia, WA
Multigenerational Suite
Attached ADU for aging parents with accessibility features.
Olympia, WA
Multigenerational Suite
Attached ADU for aging parents with accessibility features.
Olympia, WA
Studio ADU
Compact 400 sq ft studio with efficient layout.
Olympia, WA
Studio ADU
Compact 400 sq ft studio with efficient layout.
Lacey, WA
Two-Story DADU
Two-story detached ADU with 2 bedrooms.
Lacey, WA
Two-Story DADU
Two-story detached ADU with 2 bedrooms.
"Our ADU now generates $1,800/month in rental income. Best investment we ever made!"
Robert T.
Olympia, WA • Detached DADU
How We Can Help
Comprehensive Solutions
From emergency repairs to complete replacements, we provide full-service solutions tailored to your needs.
Free ADU Consultation
We'll assess your property and discuss ADU possibilities and ROI.
Permit & Zoning Experts
We handle all permits, zoning requirements, and code compliance.
Licensed & Insured
Fully licensed contractors with comprehensive insurance coverage.
Turnkey Solutions
From design to completion, we deliver move-in ready ADUs.
Get In Touch
Let Our Experts Answer Your Questions
Schedule your free consultation today. Our team is ready to help.
Ready to Add an ADU to Your Property?
Let's Bring Your Vision to Life
Contact us today for a free, no-obligation consultation.
Free estimate • No obligation • Licensed & insured