ADU Costs in Bellingham: A Detailed Breakdown for Homeowners
Building an ADU in Bellingham typically costs between $250k-$450k, depending on size, design, and site conditions. Below, we break down every expense—from permits to utility hookups—so you can budget confidently.
ADU Costs
ADU Cost Breakdown in Whatcom County
Cost Breakdown
- Design & Engineering: $15,000–$30,000
- Architectural plans, structural engineering, and energy calculations
- Tip: Prefab ADUs often include pre-approved designs, saving $5,000–$10,000
- Permits & Fees: $8,000–$20,000
- Bellingham permit fees: $4,200 (Type I) to $12,000 (Type III)
- Impact fees waived for ADUs under 1,000 sq ft
Prefab vs. Custom Builds
Prefab ADUs
- Cost: $150,000–$300,000
- Timeline: 4–6 months (factory-built modules)
Custom ADUs
- Cost: $300,000–$450,000
- Timeline: 8–12 months
Case Study: Roosevelt Neighborhood ADU
- 600 sq ft detached ADU with 1-bedroom layout
- Total cost: $260,000
- Rental income: $1,800/month
Financing Your ADU
- HELOCs: Rates from 6.5–8.5% (WECU, Peoples Bank)
- Construction loans: Convert to mortgages post-build
Citations & Sources
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Permit Fees: Bellingham Land Use Applications
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Prefab Options: Bellingham ADU Prefab Solutions
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Utility Requirements: BMC 20.10.036(B)(12)
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Cost-Saving Strategies: Whatcom Housing Alliance Recommendations
How We Help You Stay Compliant
Free Zoning Report: Share your address, and we’ll provide a customized analysis of your lot’s ADU potential.
Design Review: Our architects ensure your plans meet Bellingham’s “cottage character” guidelines.
Permit Guarantee: If your permit is denied due to our oversight, we cover revision fees.
Contact Us Today!
Make sure you stay in compliance every step of the way during the ADU building process. Contact our team today.