DADU Seattle: A Comprehensive Guide for Homeowners

As housing demand continues to rise in Seattle, Detached Accessory Dwelling Units (DADUs)—also known as backyard cottages—have become a popular solution for property owners. These units provide additional living space, serve as an affordable housing option, generate passive income, and contribute to community development. This guide will walk you through everything you need to know about DADUs in Seattle, including regulations, benefits, and how to get started with your project.

What Is a DADU?

A DADU (Detached Accessory Dwelling Unit), also known as a backyard cottage, is a second unit on the same lot as the primary residence but is a separate structure. Unlike an attached accessory dwelling unit (AADU), a DADU is detached from the main house, offering more privacy and flexibility for its occupants.

Key Features of a DADU

• Maximum Size: Up to 1,000 square feet of gross floor area.
• Standalone Structure: A detached unit separate from the primary home.
• Variety of Designs: Choose from architecturally designed layouts with options like simple rectangular forms, two available roof configurations, and optional vaulted ceilings.
• Use Cases: Ideal for graceful aging in place, hosting family members, or renting out for passive income.

Benefits of Building a DADU in Seattle

Building a DADU comes with numerous advantages for Seattle homeowners:

1. Generate Passive Income: Renting out a DADU can help offset mortgage costs and provide steady rental income.
2. Provide Family-Friendly Housing: A detached one-bedroom ADU or two-bedroom unit is perfect for families needing additional space or housing for aging parents.
3. Increase Property Value: Adding a DADU enhances your property’s value, especially in Seattle’s competitive housing market.
4. Support Community Development: Creating accessory dwelling units helps address the housing shortage by increasing the number of dwelling units in single-family zones. Additionally, DADUs offer a more affordable housing option for families who may not afford traditional homes.
5. Environmentally Friendly: With compact designs and energy-efficient features, DADUs meet Seattle’s strict energy code requirements for sustainable housing.

Boosting Accessory Dwelling Units for Diverse Housing in Seattle

“Making progress on Seattle’s urgent housing affordability needs requires not only increasing overall production, but increasing the diversity of housing available,” said Mayor Harrell.

Mayor Bruce Harrell has announced a proposal to streamline the permitting process and increase the production of accessory dwelling units (ADUs) in Seattle. This initiative aims to create more diverse and affordable housing opportunities across the city.

The proposal includes legislation to update Seattle’s existing ADU code in compliance with HB 1337, allowing two ADUs per lot and dual detached ADU configurations across all residential zones. Additionally, a companion bill is expected to encourage more family-sized homes, expand homeownership opportunities, and preserve existing homes.

The new incentives are designed to remove regulatory barriers and make the construction of ADUs more feasible for homeowners, while remaining consistent with Seattle’s building code, short-term rental code, and tree code. Since the city’s ADU rules were reformed in 2019, permitting has surged, with 987 permits issued in 2023 – a fourfold increase over 2018 levels.

The proposal is part of Mayor Harrell’s broader One Seattle Housing Agenda, which includes various efforts to support affordable housing and greater housing production in the city. The goal is to create more flexible living options, increase housing affordability and homeownership opportunities, and promote inclusive and vibrant communities throughout Seattle.

Seattle DADU Regulations and Requirements

Seattle’s adu regulations are designed to encourage the construction of DADUs while maintaining the character of its neighborhoods. Regulations also allow for the conversion of an existing unit into a DADU, provided it meets the necessary requirements. Here’s what you need to know:

Requirement	Details
Maximum Size	Limited to 1,000 square feet of gross floor area.
Owner Occupancy Requirement	Homeowners must occupy either the main house or the DADU.
Lot Coverage	Must comply with the maximum lot coverage allowed for the property.
Parking Requirements	No additional parking is required for a DADU.
Height Restrictions	The maximum height depends on site-specific factors, such as lot slope.
Energy Code Requirements	Must meet Seattle’s energy code to ensure efficiency and sustainability.
Land Use Code	DADUs must comply with Seattle’s land use code, including setbacks and neighborhood compatibility.
Environmentally Critical Areas	Properties in environmentally critical areas may face additional restrictions.

Pre-Approved DADU Plans in Seattle

To reduce costs and streamline the permitting process, the Seattle Department offers pre-approved DADU designs, also known as a pre approved DADU plan. These plans are designed to simplify construction while adhering to the city’s regulations.

Advantages of Pre-Approved DADU Plans

• Cost Savings: Avoid the expense of custom designs.
• Faster Permitting Process: Pre-approved plans meet Seattle’s requirements, expediting approval.
• Flexibility: Options include one-bedroom and two-bedroom layouts, aesthetically flexible designs, and optional vaulted ceilings.
• Neighborhood-Friendly: Adaptable to Seattle’s varied neighborhood styles.

Features of Pre-Approved DADUs

• Compact Footprints: Designed for smaller lots.
• Curbless Showers: Accessibility-friendly features for an accessible home.
• Energy Efficiency: Compliant with Seattle’s energy code requirements.

Step-by-Step Guide to Building a Seattle DADU

Building a DADU in Seattle can seem daunting, but with the right approach, the process becomes manageable and allows you to create accessory dwelling units that meet your needs. Here’s a step-by-step guide:

1. Check Zoning and Lot Suitability

• Confirm that your property is in an eligible neighborhood residential zone and that you, as the property owner, meet all the necessary requirements.
• Verify that your lot meets requirements for maximum size, lot coverage, and setbacks.

2. Develop a Site Plan

• Work with a professional to create a site plan showing the DADU’s location, utilities, and compliance with Seattle’s codes.

3. Choose a Design

• Select a plan from Seattle’s pre-approved DADU designs or work with an architect to create a custom design.

4. Submit Permit Applications

• File the necessary permits with the Seattle Department, ensuring all adu regulations and energy code requirements are met.

5. Begin Construction

• Hire a licensed contractor to build your DADU, ensuring compliance with height, footprint, and material guidelines.

6. Finalize and Utilize Your DADU

• Once construction is complete and the unit passes inspections, use your DADU as a rental, guest house, or family space.

DADU Design Options

Modern DADU designs offer flexibility and functionality to fit a variety of needs. Some popular features include:

Feature	Description
One Bedroom or Two Bedrooms	Designed to fit families, individuals, or renters.
Optional Vaulted Ceilings	Adds spaciousness and light to the living area.
Cook’s Kitchen	Fully equipped kitchens for long-term tenants or family members.
Sloping Site Adaptability	Flexible designs for properties with uneven terrain.
Two Roof Configurations	Choose between gable and flat roof styles for aesthetic and functional flexibility.

Why Seattle Homeowners Are Building DADUs

Seattle’s new ADU regulations have removed many regulatory barriers, making it easier than ever to build accessory dwelling units. Homeowners are drawn to DADUs for reasons like:

• Creating Housing: Addressing Seattle’s housing demand with additional dwelling units.
• Passive Income: Renting out a DADU is a reliable way to generate income.
• Family Needs: Housing aging parents or adult children in a detached accessory dwelling unit ensures privacy and independence.
• Architectural Flexibility: DADUs can match the style of the main house or be designed to stand out.

Ready to Build Your DADU in Seattle?

Building a DADU in Seattle is an excellent way to enhance your property’s value, generate passive income, and contribute to the city’s housing solutions. By taking advantage of pre-approved designs, understanding Seattle’s adu regulations, and following a clear step-by-step guide, you can create a detached accessory dwelling unit that fits your needs and budget.

Get started today and turn your backyard into a family-friendly, income-generating space with a DADU Seattle project!

FAQs: Detached Accessory Dwelling Units in Seattle