A standalone cottage in your backyard, up to 1,000 square feet, with its own kitchen, bath, and entrance. We check your zoning, draw it, pull the permit, and build it.
A detached ADU, sometimes called a DADU or a backyard cottage, is a full living unit built from the ground up in your yard. It has its own kitchen, its own bathroom, and its own entrance, so it lives like a small house, not a converted room. Bellingham's 2025 rules let a detached unit reach 1,000 square feet of habitable space and 24 feet tall, which is enough for a real one or two-bedroom cottage.
We start with a free feasibility check against your lot size, setbacks, and zoning, because not every lot pencils out and you should know that before you spend a dime on design. Once it does, we draw the plans, run the permit through the City of Bellingham or Whatcom County, and build a cottage that passes inspection and holds up to our wet winters. Every unit gets insulated, air-sealed, and ventilated to current Washington energy code so it stays dry and warm for the long haul.
What it actually costs.
Detached ADU $250,000 to $400,000+
SizeA studio runs far less than a two-bedroom cottage
Finish levelStandard rental finish vs. owner-quality
Site accessTight backyards and slopes add crane and labor cost
Utility runsDistance to sewer, water, and the panel drives the dig
Our four-step process.
Free feasibility check
We check your lot size, setbacks, and zoning against the City or County rules, then tell you what your lot actually allows and a realistic budget.
Design and permit
We draw the cottage, handle the engineering, and pull the full permit package with the City of Bellingham or Whatcom County.
Site work and build
We run utilities, pour the foundation, frame, and build to current energy code, with you in the loop the whole way.
Final inspection and walkthrough
We pass final inspection, walk the finished cottage with you, and fix anything on the punch list before we leave.
Why hire a real crew for this.
Up to 1,000 sq ft of habitable space under the 2025 Bellingham rules
Its own kitchen, bath, and private entrance for a renter or family
Insulated, air-sealed, and ventilated to current WA energy code
Zoning, plans, permits, and inspections all handled by us
A written, line-item quote before we break ground
Frequently asked questions.
How much does a detached ADU cost in Bellingham?
A ground-up detached ADU in Bellingham and Whatcom County typically runs $250,000 to $400,000 or more, which pencils out to roughly $400 to $550 per square foot. A small studio lands lower; a finished two-bedroom cottage with long utility runs lands higher. The big drivers are size, finish level, site access, and how far we have to run sewer, water, and power to the unit. We give you a line-item number after a free site visit.
How big can a backyard cottage be in Bellingham?
Under Bellingham's 2025 ordinance update (BMC 20.10.036), a detached ADU can have up to 1,000 square feet of habitable space and stand up to 24 feet tall, and most single-family lots can now have up to two ADUs. The exact footprint your lot allows depends on setbacks and lot coverage, which we confirm during the free feasibility check before any design work starts.
How long does it take to build a detached ADU?
Plan on 6 to 12 months from the first design meeting to final inspection. Design and engineering take a few weeks, permit review with the City or County can run one to three months depending on the queue, and construction of a cottage is usually three to five months. We give you a realistic schedule up front and tell you what tends to slow it down.
Ready for a free detached adu quote?
Tell us about your project and your lot. We'll reply within 15 minutes during business hours.