How much does an ADU cost in Bellingham?
It depends on the type. A detached backyard cottage runs $250,000 to $400,000 or more (roughly $400 to $550 per square foot), a garage conversion runs $80,000 to $150,000, and a basement apartment conversion runs $90,000 to $180,000. The drivers are size, finish level, site access, and how far we run utilities to the unit. We run a free feasibility check on your lot and hand you a line-item number, so you know what your project costs before you commit.
Can I build an ADU on my lot in Bellingham?
Often yes, and more easily than a year ago. Under Bellingham's 2025 ordinance update (BMC 20.10.036), most single-family lots can now have up to two ADUs, a detached unit can reach 1,000 square feet and 24 feet tall, and off-street parking requirements are waived in the current window. Whether your specific lot works depends on setbacks and lot size, which is exactly what our free feasibility check confirms before you spend anything on design.
Do I have to live on the property to rent the ADU?
For most city lots, not after July 1, 2026. Bellingham's owner-occupancy requirement sunsets on that date, which means you will be able to rent both the main house and the ADU rather than having to live in one of them. The rule can vary by address and by whether you are inside the city or in Whatcom County, so we confirm it for your specific property during the feasibility check.
Is converting my garage cheaper than building new?
Usually yes on total dollars, because a garage is smaller and the structure already exists. But the cost per square foot ends up similar to a new cottage once you add the kitchen, bath, insulation, egress, and utilities, since those cost the same whether the unit is new or converted. We give you both numbers so you can compare a garage conversion against a detached ADU for your lot.
Who handles the permit and the inspections?
We do, start to finish. We assemble the full permit package, submit it to the City of Bellingham if you are inside city limits or to Whatcom County if you are outside, manage the plan review including answering reviewer comments, and carry it to an approved permit. Then we schedule and handle the inspections during construction, so you do not have to navigate the counter yourself.
Are you licensed and insured?
Yes. Bellingham ADU Co. is operated by Apex Builderz LLC, a licensed, bonded, and insured Washington general contractor (WA Contractor Reg. # APEXBBL749B1, UBI 604-945-342). We carry general liability insurance, and we are happy to show you the paperwork. Just ask.
What is the best time of year to build an ADU in Bellingham?
We build year-round. Our wet winters mainly affect the foundation and dry-in stages, so we sequence those for the drier windows when we can, but a project's timeline is driven far more by design and permit review than by the season. Because permitting takes time, starting in fall or winter often means you are ready to build when spring opens up.
How long does the whole thing take, permits and all?
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 runs one to three months depending on the queue, and construction is usually three to five months. We give you a realistic schedule up front and tell you honestly what tends to slow it down.
