Architecture, Custom Residential, Landscape Architecture, Multifamily Residential
Navigating the World of Backyard Buildings
When it comes to backyard buildings, there are many things to consider. The first is: what exactly is a backyard building? From accessory structures to detached accessory dwelling units to garages, we’re breaking down the three main types of backyard buildings and how they function on your property.
February 26, 2026
If you’ve ever stood in your backyard, coffee in hand, dreaming about that perfect studio space, workshop, or rental unit, you’ve probably wondered: “What exactly can I build back here?”
The answer, like most things in the world of zoning and permitting, is complicated.
Whether you’re in Seattle proper or another Washington municipality, understanding the difference between an accessory structure (like a shed), a detached Accessory Dwelling Unit (DADU), or a garage isn’t just semantic, it’s the difference between a smooth permitting process and months of bureaucratic headaches.
So, let’s dive into this alphabet soup of building types, shall we?
Your Big Three options.
Before we get into the nitty-gritty of setbacks and square footage limits, let’s establish what we’re talking about here. In the world of Western Washington zoning, your backyard dreams generally fall into three categories: accessory structures, detached accessory dwelling units, and garages.
Accessory Structures
These are your basic outbuildings. Think tool sheds, art studios, or a workshop where you’ll definitely start that pottery hobby. They’re supplementary to your main house and generally don’t include living amenities, like plumbing.
Detached Accessory Dwelling Units
Detached accessory dwelling units, or DADUs, are separate living spaces with their own kitchen, bathroom, and sleeping areas. These are your backyard cottages, converted garages with full amenities, or purpose-built rental units.
Garages
Garages are, well, garages. But they come with their own set of rules, especially when you start talking about attached versus detached, or, heaven forbid, converting one into something else.
Accessory structures are the most straightforward option.
Let’s start with the most straightforward of the bunch: accessory structures. These are the workhorses of the backyard building world and, in most Western Washington jurisdictions, they’re reasonably uncomplicated to build.
What Counts as an Accessory Structure
In Washington State, one-story detached buildings used for storage sheds, playhouses, or similar are considered accessory structures. The key thing to remember about accessory structures is that they’re meant to be just that: accessory to your main dwelling.
They’re not designed for living, and the moment you start adding in kitchens or bathrooms, you’ve crossed into DADU territory.
The permitting process is usually straightforward, the construction costs are reasonable, and you’re not dealing with the complexity of creating livable space.
When Accessory Structures Make Sense
Accessory structures are perfect when you need:
- A workshop or art studio.
- Extra storage that doesn’t require utilities.
- A home office that doesn’t need plumbing.
- A place for hobbies that might be too messy or noisy for the main house.
DADUs add usable living space.
Now we’re getting into the exciting stuff. DADUs are the current poster child of progressive housing policy in Western Washington, and for good reason. They’re a way to add density to existing neighborhoods without dramatically changing the character of single-family areas.
Single-family-only zoning has officially ended in Seattle, opening the door for big changes in how we think about residential density. Interim legislation has opened new possibilities for homeowners looking to add rental income or create multi-generational housing in their previously single-family-zoned lot.
What Makes a DADU a DADU
An accessory dwelling unit of any kind is a separate living space within a house or on the same property as an existing house. You can have an attached accessory dwelling unit (AADU) or a detached accessory dwelling unit (DADU). We’re talking about the detached kind here.
The key word for either type is “living space.” This isn’t just a fancy shed with a hot plate. We’re talking about a fully functional dwelling unit that could serve as someone’s primary residence.
A DADU, though detached from the main house, must include:
- A kitchen or kitchenette.
- A bathroom.
- Sleeping accommodations.
- Separate entrance from the main dwelling.
Regional Variations
While Seattle has been leading the charge on DADU-friendly policies, other Western Washington jurisdictions are following suit, though often with more conservative approaches. Creation of habitable space in existing garages and sheds requires an Accessory Dwelling Unit (ADU) Permit in most zoning districts.
Cities like Tacoma, Bellevue, and Redmond each have their own regulations, generally following similar principles but with local variations on size limits, design requirements, and permitting processes. Your architect can help you navigate these requirements and processes.
Garages aren’t just for cars.
Often overlooked in discussions of accessory buildings, garages occupy a unique position in the hierarchy of backyard structures. They’re utilitarian by nature but increasingly serve multiple functions in our space-constrained urban environments.
Attached Garages vs. Detached Garages
The distinction between attached and detached garages matters more than you might think. Attached garages are considered part of your primary dwelling for many regulatory purposes, which means they count toward your total floor area ratio (FAR) and must meet different fire safety requirements.
Detached garages, on the other hand, are treated more like accessory structures, with their own setback requirements and height limitations. This distinction becomes crucial when you’re planning additions or considering converting garage space for other uses.
The Garage Conversion Conundrum
Here’s where garages get really interesting from a zoning perspective. Want to convert that garage into a home office? Probably fine, as long as you’re not adding plumbing or creating habitable space. Want to turn it into a rental unit? Now you’re in DADU territory, with all the permitting complexity that entails.
The key issue is habitability. The moment you add a kitchen and bathroom to create truly livable space, your garage conversion becomes an ADU project, subject to all the associated regulations and requirements.
Making the right choice for your property.
So, which type of backyard building is right for you? The answer depends on your specific needs, budget, and long-term goals.
Choose an accessory structure if you:
- Need storage or workshop space.
- Want a simple, relatively inexpensive project.
- Don’t need plumbing or full utilities.
- Prefer a straightforward permitting process.
Choose a DADU if you:
- Want to generate rental income.
- Need housing for family members.
- Are comfortable with a more complex project.
- Have a suitable lot and adequate budget.
Choose a garage (or garage conversion) if you:
- Need vehicle storage plus other functions.
- Want to maximize existing structures.
- Are looking for a middle-ground option between simplicity and functionality.
The key to backyard buildings is understanding that each type of structure serves different needs. Start with a clear understanding of your goals. With proper planning and realistic expectations, your backyard building project can be a rewarding addition to your property and your life. After all, good neighbors make good neighborhoods, and good neighborhoods are what make Western Washington a wonderful place to live.
