Bellingham & Whatcom County
What Will Your ADU Actually Cost?
Answer a few questions and see your ballpark before you talk to anyone. A full ADU runs $450–$650/sq ft all-in, permitting included — this tells you where your project lands.
3 Simple Steps to Your ADU
Free 30-Minute Consultation
A real conversation about your lot, the rules, and the cost.
Full Permit Package
Land use + building permits. We handle everything.
Letter of Intent + Build
Architect, permits, builder — all in one.
FREE 30-MINUTE CONSULTATION · FREE PERMITS WHEN WE BUILD
Questions? Call (360) 594-0120 — Mon–Fri 8am–5pm
Ballpark Pricing
What It Costs Per Square Foot
Three tiers, depending on how far you want to take the structure. Not every project needs to be a full dwelling unit.
Unpermitted Accessory Structure
~$200/sq ft
Insulated, enclosed studio, office, or bonus room. Power only — no plumbing or water, not a dwelling unit.
No building permit required. Typical 100–400 sq ft: $20,000–$80,000.
Permitted Accessory Structure
~$300/sq ft
Permitted and built on a real foundation for use as a bedroom, office, or studio. Still no kitchen or plumbing.
Includes permitting and foundation. Typical 200–500 sq ft: $60,000–$150,000.
Full ADU / DADU
$450–$650/sq ft
Permitted dwelling unit with kitchen, bathroom, and full utility connections. Rentable, financeable, appraisable.
All-in: design, permitting, construction, utilities. Typical 500–1,000 sq ft: $225,000–$500,000.
No Minimum Project Size
A 120 sq ft insulated backyard office is real work to us, same as a 1,000 sq ft DADU. If you only need a quiet room with power and insulation, we will build exactly that and nothing more.
Garage Conversions
Converting a garage into a non-dwelling bonus room is quoted per project after a site visit — the existing structure drives too much of the cost to publish a rate. Garage-to-ADU conversions price at the full dwelling tier.
Three Ways We Build
Prefab, Modular, or Site-Built
Small Prefab Units
We build the unit in the shop, deliver it, then assemble and finish it on site. Fastest path for offices, studios, and bonus rooms.
Full Modular Units
A complete factory-built standalone unit trucked in and set on your site. Fixed price, compressed timeline, site prep runs in parallel.
Full Site-Built
Built entirely on site from the ground up. Adapts to any lot, slope, or custom design — the right call for complex properties.
Modular is the fastest path to a permitted dwelling unit. Browse all 14 prefab floor plans, 200–900 sq ft →
ADU Guides & Resources
Everything you need to know before building an ADU in Bellingham and Whatcom County.
ADU Cost Breakdown
How much does an ADU cost in Whatcom County? Complete 2026 pricing by type.
EssentialADU Laws & Regulations
Bellingham and Whatcom County ADU rules, setbacks, and size limits.
Start HereCan I Build an ADU?
Quick eligibility checklist based on your lot, zoning, and property type.
FinanceADU Financing Options
HELOCs, construction loans, and ADU-specific financing for WA homeowners.
PlanningConstruction Timeline
Month-by-month breakdown from design to move-in for Whatcom County projects.
InvestmentIs an ADU Worth It?
ROI analysis, rental income projections, and property value impact.
2026 Whatcom County ADU Laws
Everything you need to know about the new regulations and opportunities.
2025 Washington State ADU Law Changes (HB 1337)
Major statewide deregulation for easier building.
- Right to Build: All Washington cities/counties must allow ADUs by right.
- No Owner Occupancy: Owner-occupancy requirements eliminated statewide. You can rent both units.
- Reduced Setbacks: Setbacks reduced to 5ft in many cases to fit more lots.
- Impact Fees: Limitations on impact fees for ADUs under 1,000 sqft.
Meet Your Team
You don't get handed off. You get a team.
Loren
Builder
Loren carries your project from first call through final inspection. He is your single point of contact the whole way.
Carlos
Builder
Carlos runs Monarca Construction, a licensed WA State general contractor, and builds ADUs start to finish alongside Loren.
Jorge
Project Designer
Jorge leads design and permitting on custom builds, translating your site and goals into drawings that clear review.
Jordan
Systems & Project Coordination
Jordan builds the systems behind the process — the GIS feasibility pipeline, project tracking, and client communication.
Frequently Asked Questions
Whatcom County
Where We Build
Bellingham, Ferndale, Lynden, Blaine, Everson and unincorporated Whatcom County. We come to your property — there's no office to visit.
