ADU design in Bellingham isn't one-size-fits-all. Your lot size, setback requirements, zoning district, orientation, existing structures, and personal needs all shape the right design for your property. That's why every Bellingham ADU design we produce starts from scratch — no cookie-cutter plans, no imported templates from other markets.
Our design process starts with the data — lot dimensions, setbacks, utility locations, and zoning constraints — and works backward into a floor plan that maximizes your buildable area while meeting all code requirements. No wasted square footage. No surprises at permitting.
We also integrate sustainable building practices into every design from the start — passive solar orientation, high-performance envelopes, and right-sized mechanical systems. For a complete picture of what an ADU project costs in our area, see our Whatcom County ADU cost breakdown.
Our Design Approach
Site-Specific
Every design begins with your property's actual dimensions, setbacks, and constraints. We use parcel data and site measurements to determine exactly where an ADU can be placed and how large it can be.
Code-Compliant
Designs are drawn to meet Bellingham's BMC 20.10.036 or Whatcom County's WCC 20.80.910 from day one. Height limits, lot coverage, setbacks, open space — all resolved before you see a floor plan.
Climate-Optimized
Window placement, roof orientation, and overhangs are designed for Bellingham's specific solar path and rainfall patterns. South-facing glazing for passive solar gain, covered entries for rain protection.
Privacy-Conscious
We position windows, entries, and outdoor spaces to protect both your privacy and your neighbors'. Thoughtful siting reduces overlooking and maintains neighborhood character.
ADU Types We Design
Detached ADU (DADU / Backyard Cottage)
Typical size: 400–1,000 sq ft (1,200+ with CUP)
Freestanding structures in your backyard. Maximum flexibility in layout and design. Best for larger lots with adequate setback clearance. See our detached ADU service page for construction details.
Best for: Birchwood, Columbia, Happy Valley, Samish — lots with 7,000+ sq ft
Attached ADU (Addition)
Typical size: 300–1,000 sq ft
Built onto your existing home as a side or rear addition. Shares one or more walls with the primary dwelling, reducing construction costs.
Best for: Sunnyland, Lettered Streets, Roosevelt — tighter lots where setbacks limit detached options
Garage Conversion
Typical size: 400–600 sq ft (typical)
Convert an existing detached or attached garage into living space. Often the most affordable path since the shell already exists. Learn more about our garage conversion process.
Best for: Any neighborhood — especially lots with oversized or underused garages
Basement ADU
Typical size: Varies (exempt from 1,000 sq ft limit if home is 5+ years old)
Convert existing basement space into a self-contained unit. Bellingham offers a special size exemption for basement conversions in older homes.
Best for: Sehome, Fairhaven, South Hill — older homes with full or walkout basements
Above-Garage ADU
Typical size: 400–800 sq ft
Build living space above a new or existing garage. Efficient use of footprint on lots where ground-level space is limited.
Best for: Cordata, Barkley, newer neighborhoods with alley access
Design Considerations by Lot Size
| Lot Size | Best ADU Options | Key Design Constraints |
|---|---|---|
| Under 5,000 sq ft | Attached ADU, basement conversion | Tight setbacks, lot coverage limits, consider reduced setback agreement |
| 5,000–8,000 sq ft | Small detached, garage conversion, attached | Setback compliance critical, compact floor plan design |
| 8,000–15,000 sq ft | Any type up to 1,000 sq ft | Good flexibility, consider 2 ADU configuration |
| 15,000+ sq ft | Large detached, multiple ADUs, CUP for oversized | Maximum flexibility, consider lot subdivision potential |
Custom ADU Floor Plans for Bellingham Lots
Bellingham lots come in every shape and size — narrow urban parcels in the Lettered Streets, generous corner lots in Birchwood, sloped sites on South Hill, and rural acreage near Maple Falls. Off-the-shelf floor plans rarely account for the specific setbacks, utility easements, and topography that define what's actually buildable on your property.
Our custom floor plans are drawn to fit your lot precisely. We start with a GIS data pull and on-site measurement, then overlay zoning setbacks, utility locations, and access requirements to define the exact buildable envelope. The floor plan is designed within that envelope — not adapted to it after the fact.
Common floor plan configurations we design include:
- Open-plan studios (400–600 sq ft) — efficient single-level layouts ideal for rental income or aging-in-place
- Two-bedroom single-story (600–850 sq ft) — the most popular configuration for long-term tenants and family members
- Two-story with garage below (800–1,000 sq ft) — maximizes living space on compact lots while solving parking
- Loft-style cottages (500–750 sq ft) — vaulted ceilings with sleeping loft, ideal for narrow lot footprints
Want to see what these look like built? Browse our ADU project portfolio for real examples with costs and timelines. Ready to explore what fits your lot? Start with a free feasibility report.
What's Included in Our Design Package
Design Process Timeline
Site Analysis & Feasibility
Property measurement, GIS data pull, zoning review, and constraint mapping. We identify exactly what's buildable on your lot.
Concept Design
Two to three preliminary floor plan options with site plans showing ADU placement, setbacks, and outdoor space. We present these for your review and feedback.
Design Development
Refine the selected concept into detailed architectural drawings. Coordinate structural engineering, energy modeling, and utility planning.
Permit Drawings
Finalize construction documents for permit submission. Loren reviews for code compliance and submits to the planning department.
Start With Your Property
Every great ADU design starts with understanding your lot. Get a free feasibility report that maps your property's constraints and possibilities.
Get Your Free Feasibility ReportCheck Your Property's ADU Potential
Get a free feasibility report based on Whatcom County GIS data and 2025 land use rules.
Get Your Free Feasibility Study
