For many Eastside homeowners, the decision to expand living space is a direct response to an evolving lifestyle. Whether you need a private suite for aging parents, a source of rental income, or simply more room for your growing family, adding square footage is a powerful investment. Accessory Dwelling Units (ADUs) and traditional home additions are two of the most effective ways to achieve this, but they follow very different planning, permitting, and construction paths. Understanding these differences is the first step in a successful project. This guide will walk you through the critical considerations for ADU and home addition services on the Eastside, helping you make an informed choice for your property’s home remodel.
ADU vs. Home Addition: Which One Do You Need?
While both projects add valuable square footage, their function and legal classification are distinct. Choosing the right path depends entirely on how you intend to use the new space.
An Accessory Dwelling Unit (ADU) is a complete, self-contained living unit situated on the same lot as a single-family home. To qualify as an ADU, the space must include its own entrance, kitchen, and bathroom. ADUs can be detached (a separate backyard cottage) or attached (a converted garage or basement apartment). They are ideal for:
- Generating rental income to offset a mortgage.
- Providing independent living for aging parents or adult children.
- Creating a private guesthouse for visitors.
A home addition, by contrast, is an expansion of your primary residence’s existing footprint. It does not create a separate dwelling. Instead, it adds one or more rooms that are integrated into the main house. Home additions are the right solution for:
- Adding bedrooms for a growing family.
- Creating a dedicated home office or fitness room.
- Expanding a kitchen or living area for better flow and entertaining.
Permitting requirements differ significantly between these two project types. ADUs are subject to specific zoning rules regarding size, owner-occupancy, and location, while additions are primarily governed by lot coverage and setback regulations.
Navigating ADU Permits in Redmond
The City of Redmond has progressively updated its regulations to encourage the development of Accessory Dwelling Units, recognizing them as a key solution to housing needs. However, the process remains detailed and requires a thorough understanding of local codes. As an experienced contractor working in Redmond, Eastside Kitchen & Bath manages this entire process so you don’t have to.
Key aspects of the ADU permit process in Redmond include:
- Attached vs. Detached Rules: Redmond allows for both attached and detached ADUs. Detached ADUs (DADUs) have specific regulations, including a maximum size of 50% of the primary dwelling’s square footage (capped at 1,500 sq ft) and a height limit of 28 feet. (See the Redmond Zoning Code, RZC 21.08.220.)
- Setback Requirements: Your detached ADU must conform to the same setback and lot-coverage standards required of a single-family home in your residential zone. (See RZC 21.08.220.)
- Owner-Occupancy: For long-term rentals (leases of 12 months or more), Redmond does not require the owner to live on-site, provided both units are under signed 12-month leases. Owner-occupancy applies only to short-term and vacation rentals.
- Permit Pathway: The process typically involves a pre-application meeting, followed by design review, civil review for site work, and finally the building permit application. Timelines can fluctuate based on city workload and project complexity.
Our team navigates these steps on your behalf, preparing all necessary architectural plans and documentation to ensure a complete submission and review.
ADU and Addition Permits in Sammamish
Planning a home addition in Sammamish or an ADU involves a different set of local regulations. The city has its own specific requirements that influence design and scheduling, which is why local experience is critical.
When planning a project in Sammamish, here is what you can expect:
- Lot Coverage Rules: Sammamish limits both lot coverage and impervious surface, and the exact figures depend on your zone (for example, maximum lot coverage of 40% in R-4 and 50% in R-6). Building an ADU can earn a one-time 5% increase in allowable lot coverage. (See the Sammamish lot coverage handout and SMC 21.04.030.)
- Height Limits: The maximum building height for residential structures is generally 35 feet, which can influence two-story designs. (See SMC 21.04.030.)
- Permit Timeline: Review timelines in Sammamish can differ from those in Redmond. We build our project schedules around realistic city review windows, which can run several weeks to a few months for a complete application, depending on scope and city workload.
- Tree Preservation: Sammamish places a high value on its natural landscape, and projects must often include a tree preservation plan if significant trees are on the property.
By understanding these local nuances, Eastside Kitchen & Bath can create a realistic project schedule and avoid costly delays.
The Design-Build Advantage for ADU and Addition Projects
Unlike an interior remodel, ADUs and home additions are complex construction projects that involve structural engineering, civil site planning, and architectural design. When these services are hired separately in a traditional “design-bid-build” model, homeowners are often caught in the middle. If a design created by an independent architect proves too expensive to build, you are left with plans you cannot use or face costly redesign fees and change orders from the builder.
This is where the design-build model offers a clear advantage. With a design-build ADU contractor, you have one team and one contract from start to finish.
- Integrated Planning: Our designers, estimators, and project managers work together from day one. Design decisions are made with a full understanding of build costs, ensuring your project stays on budget.
- Clear Communication: You have a single point of contact. There is no finger-pointing between an architect and a builder if challenges arise.
- Efficiency: With our in-house team managing design, permits, and construction, we can streamline the schedule and move your project forward without unnecessary hand-offs or delays.
For projects as complex as an ADU or addition, this integrated approach is the key to a successful, low-stress experience.
Frequently Asked Questions About ADU and Home Additions on the Eastside
An ADU is a separate, independent living space with its own kitchen, bathroom, and entrance. A home addition expands the main house without creating a separate unit. ADUs can be used for rental income or multigenerational living, while additions typically add bedrooms or living space for the primary household.
Permitting timelines can vary depending on the city’s workload and the complexity of your project. Generally, you can expect the permit review process to take several months. A design-build firm with local experience can help ensure your application is complete and accurate, which helps avoid unnecessary delays.
Yes, most Eastside cities, including Redmond and Sammamish, allow homeowners to build and rent out ADUs. However, there are often owner-occupancy rules, meaning the property owner must live in either the main house or the ADU. We can confirm the specific regulations for your city.
The cost of a home addition varies widely based on the size, complexity, level of finishes, and site conditions. These projects involve significant structural, electrical, and plumbing work. After an initial consultation, we can provide a detailed estimate based on your specific project goals.
Conclusion
ADU and home addition projects move at a different pace than interior remodels, and the permit process is the main reason why. For homeowners in Redmond and Sammamish, each city has distinct rules and timelines that need to be built into the schedule before design is finalized. The projects that stay on track are the ones with complete, accurate permit applications at first submission. Getting there requires local permit knowledge and a design team that builds plans to be buildable, not just presentable.
Why Eastside Kitchen & Bath Is the Right Partner for Your ADU or Home Addition
With nearly 20 years of experience completing permitted projects in Redmond, Sammamish, Bellevue, and across the Eastside, Eastside Kitchen & Bath has a deep understanding of what it takes to successfully expand your home. Our full-service design-build process means our in-house team handles everything: architectural design, engineering, permit submission, and all phases of construction.
You’ll work with a dedicated EKB project manager from kickoff to completion, never an outsourced contractor. We believe in accountability and clear communication. Our expertise in local building codes and our integrated approach to home addition services minimize risks and ensure your new space is built to the highest standards of quality and craftsmanship. Ready to find out what’s possible on your lot? Get a free estimate and start the conversation.