A backyard cottage is a Detached Accessory Dwelling Unit (DADU) — a fully independent, code-compliant home built in your backyard. In Seattle, “backyard cottage” and “DADU” are used interchangeably, and they're governed by SMC 23.44.041. They're one of the most popular ways Seattle homeowners add rental income, house aging parents, create a private home office, or build long-term equity.
You may hear them called DADUs, backyard homes, granny flats, or laneway houses — they're all the same thing: a permitted, permanent dwelling on your existing residential lot. Since Seattle's landmark 2019 ADU reform (Ord 125791) and Washington's HB 1337, most Seattle RS-zoned properties now qualify for at least one backyard cottage, and many can have two ADUs per lot.
This guide covers everything Seattle homeowners need to know about building a backyard cottage: design options, costs, local regulations under SMC 23.44.041, and the step-by-step process from first call to move-in.
Why Seattle Homeowners Are Building Backyard Cottages
Seattle's combination of extreme housing demand, rising property values, and progressive ADU laws makes backyard cottages one of the strongest investments a homeowner can make. Here are the most common reasons our clients build:
Rental Income
Seattle's vacancy rate is below 3%, and the city's tech sector drives year-round rental demand. A one-bedroom backyard cottage rents for $2,000–$2,800/month, generating $24,000–$33,600 in annual gross income. Washington's zero state income tax makes the after-tax return even more favorable.
Aging Parents
A backyard cottage lets parents live independently while staying close to family. The separate structure provides privacy for both households, and single-story designs with accessible features make aging in place practical. In-home caregiving in Seattle costs $25–$35/hr — a well-designed ADU is often a far more cost-effective long-term solution.
Home Office or Studio
Remote workers and creative professionals benefit from a dedicated workspace with true separation from the main home. A backyard cottage provides the focus of an office with a zero-minute commute. The space also doubles as a guest suite when needed.
Property Value
A well-built backyard cottage adds $150,000 to $250,000+ in appraised property value in Seattle's market. When you eventually sell, the cottage is a major differentiator — buyers pay a premium for properties with income-generating potential.
Design Options by Size
Seattle's SMC 23.44.041 allows backyard cottages up to 1,000 sq ft (or 60% of primary dwelling). The right size depends on your goals and budget — a studio maximizes ROI per square foot, while a two-bedroom commands the highest total rent and broadest tenant appeal.
Studio (400–500 sq ft)
Open floor plan with combined living/sleeping area, full kitchen, and bathroom. Ideal for a home office, guest suite, or single-occupant rental. Lowest total cost to build.
1-Bedroom (600 sq ft)
Separate bedroom, living room, full kitchen, and bathroom. The most popular backyard cottage size in Seattle — comfortable for one or two people and commands strong rents.
2-Bedroom (800–1,000 sq ft)
Two bedrooms, living room, full kitchen, and one or two bathrooms. Suitable for a small family, roommates, or aging parents who want space and privacy.
Costs are estimates for Seattle projects and include design, permitting, construction, and utility connections. Actual costs vary based on site conditions, finishes, and market conditions.
Seattle Regulations for Backyard Cottages (SMC 23.44.041)
Seattle regulates backyard cottages (DADUs) under SMC 23.44.041. Here are the key requirements as of 2026:
Maximum Size: 1,000 sq ft (or 60% of primary)
Seattle caps DADUs at 1,000 square feet of habitable space, or 60% of the primary dwelling square footage, whichever is less. In some cases (larger lots, specific zones), 1,200 sq ft may be achievable. This allows for a comfortable two-bedroom layout in most configurations.
Setbacks: 5 ft Rear and Side (Most Zones)
Rear and side setbacks for DADUs are typically 5 feet in most Seattle RS zones. Under HB 1337, the city cannot require greater setbacks for an ADU than for the primary dwelling. Corner lots and lots adjacent to alleys may have different configurations — our feasibility study determines exact setbacks for your parcel.
Height: Up to 24 ft (Flat Roof) or 28 ft (Sloped Roof)
Detached ADUs can be up to 24 feet tall for flat or low-pitch roofs, and 28 feet for sloped (pitched) roofs in most Seattle residential zones. This allows for two-story designs with lofts where lot conditions permit.
No Owner-Occupancy Requirement (Since 2019)
Seattle removed the owner-occupancy requirement for DADUs with Ord 125791 in 2019, confirmed statewide by HB 1337. You do not need to live on the property. Both the main house and the backyard cottage can be rented out. See our owner-occupancy guide for details.
Transit Parking Exemption
No additional off-street parking is required for DADUs on lots within ½ mile of a Link Light Rail station or a RapidRide stop. Most Seattle neighborhoods qualify. Properties outside the transit exemption area may need one additional parking space.
SMA Consideration (Waterfront Neighborhoods)
Properties within 200 feet of the Ordinary High Water Mark (OHWM) are subject to the Shoreline Management Act. This does not prohibit DADUs — it adds a shoreline review process and may impose additional setbacks from the shoreline. Affects neighborhoods near Lake Washington, Puget Sound, and major streams. SMA review adds $5K–$15K to project soft costs.
Cost Breakdown
Backyard cottage costs in Seattle break down into several categories. Understanding where the money goes helps you make informed decisions about where to invest and where to economize.
| Cost Category | Typical Range | Notes |
|---|---|---|
| Design & Engineering | $18,000–$35,000 | Architecture, structural, MEP, Seattle energy code compliance |
| Permitting & Fees (DCI) | $8,000–$20,000 | Seattle DCI land use, building permit, and utility connection fees |
| Site Work | $20,000–$50,000 | Excavation, grading, foundation, utility trenching. Seattle slopes add cost. |
| Construction | $270,000–$600,000+ | Framing, roofing, siding, insulation, all interior finishes. Seattle labor rates. |
| SPU/SCL Connections | $10,000–$25,000 | Seattle Public Utilities water/sewer, Seattle City Light electrical laterals |
| Landscaping & Exterior | $5,000–$20,000 | Pathways, plantings, fencing, site restoration |
For a comprehensive breakdown with specific cost scenarios, see our ADU costs guide for King County.
Design Inspiration
Seattle's Pacific Northwest setting calls for designs that blend with the landscape and neighborhood character. Here are three popular design directions for backyard cottages:
Modern Farmhouse
Board-and-batten siding, metal roof, covered porch, large windows. Clean lines with a warm aesthetic. Pairs well with traditional Seattle neighborhoods like Columbia City, Fremont, and Ravenna.
Pacific NW Contemporary
Shed roof, natural wood and fiber cement siding, floor-to-ceiling windows, open plan. Maximizes natural light — critical in Seattle. Popular in Capitol Hill, Ballard, and Beacon Hill.
Classic Cottage
Gabled roof, horizontal lap siding, window boxes, covered entry. Blends seamlessly with older Seattle neighborhoods like Wallingford and the Central District. Looks like it's always been there.
Not sure which direction is right for your property? Our ADU design page shows more options, or start with a feasibility study that includes design recommendations tailored to your lot and neighborhood.
Steps to Build Your Backyard Cottage in Seattle
Building a backyard cottage in Seattle follows a clear process. Here is what to expect at each stage:
Free Feasibility Study
We analyze your specific parcel using Seattle GIS data (seattle.gov/sdci) — zoning (RS, RSL, LDT), setbacks per SMC 23.44.041, lot coverage, utilities, and any special conditions (SMA overlay, critical areas). You get a clear answer on what you can build, where on your lot it goes, and a preliminary budget.
Request your free feasibility studyDesign & Architecture
Choose from our proven floor plans or work with our team on a custom design. We handle schematic design, structural engineering, MEP (mechanical, electrical, plumbing), energy code compliance per Seattle's stringent green building requirements. Most designs take 4–6 weeks.
Explore design optionsPermitting
We prepare and submit all permit applications to Seattle DCI (city properties) or King County DPER (unincorporated areas). Our team handles land use review, building permit, and utility connections with SPU and SCL. Experience with Seattle permitting means fewer revision cycles.
Learn about permittingConstruction
Our crew handles everything from site preparation through final finishes. Typical construction takes 6–9 months for a detached backyard cottage in Seattle. We provide regular progress updates and a fixed schedule.
View our processFinal Inspection & Move-In
We coordinate all final inspections with Seattle DCI, obtain your Certificate of Occupancy, and complete the final walkthrough. Your backyard cottage is ready for move-in or rental.
See full timelineFind Out What You Can Build
Every backyard cottage project starts with understanding your lot. Our free feasibility study analyzes your specific parcel — zoning under SMC 23.44.041, setbacks, site conditions — and tells you exactly what's possible.
Get Your Free Feasibility StudyNo obligation. 48-hour turnaround.
Frequently Asked Questions
How much does a backyard cottage cost to build in Seattle?
A backyard cottage (DADU) in Seattle typically costs between $450,000 and $800,000+ depending on size and finishes. A basic 400–500 sq ft studio starts around $250,000–$350,000. A mid-range 600 sq ft one-bedroom runs $360,000–$490,000. A fully finished 800–1,000 sq ft two-bedroom with premium finishes costs $540,000–$800,000+. These prices include design, permitting, site work, construction, and utility connections — totaling $450–$650 per square foot in Seattle.
How big can a backyard cottage be in Seattle?
Seattle (SMC 23.44.041) allows detached ADUs up to 1,000 square feet, or 60% of the primary dwelling's square footage, whichever is less — in most cases. Properties in some zones can reach 1,200 sq ft. This is enough for a comfortable two-bedroom unit. The actual size you can build depends on your lot: setback requirements, lot coverage limits, and the position of your existing home all factor in. Our feasibility study determines the exact maximum for your specific property.
Do I need to live on the property to rent out a backyard cottage in Seattle?
No. Seattle removed the owner-occupancy requirement for DADUs in 2019 (Ord 125791), and Washington State confirmed this statewide under HB 1337. You can own a property with a main house and a backyard cottage and rent both units out — you do not need to live in either one. This makes backyard cottages a viable investment property strategy.
How much rental income can a backyard cottage generate in Seattle?
Backyard cottages in Seattle rent for $2,000 to $3,500 per month depending on size, finishes, and location. A one-bedroom in a desirable neighborhood like Capitol Hill, Fremont, or Columbia City can command $2,200–$2,800/month for long-term rental. Annual gross rental income of $24,000–$42,000 is typical. Seattle's housing shortage and strong employment base keep vacancy rates extremely low.
Your Backyard Cottage Starts Here
Whether you're building for rental income, family, or a private workspace, we'll guide you from first conversation to move-in day. Start with a free feasibility study to see what's possible on your Seattle lot.
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