Learn all about DADUs during episode 105, Can You DADU? on the Don't Live with It. Love It.® podcast by CRD Design Build.
Also known as detached accessory dwelling units, or DADUs, backyard cottages are small, standalone houses built behind your main home. They allow you to maintain your privacy and all the square footage in your main house while creating extra living space. Homeowners often opt to build these over a new garage.
Recently we completed a two-story DADU over a new garage in Wallingford. We tore down the old garage and built this stunning DADU in its place. To see more check out - Wallingford DADU
Technically, Seattle does not allow so-called tiny homes that do not rest on their own foundation:
Tiny houses on wheels are treated like camper trailers. You cannot live in a tiny house on wheels (or similar equipment such as RVs and boats) on lots in Seattle city limits. If your tiny house has wheels you need to follow parking rules for large vehicles. [Seattle Department of Construction and Inspections]
Homeowners choose to construct backyard cottages (DADUs) for a variety of reasons, and a cottage can be put to different uses over the years.
A common reason to build a cottage is to use it as a long- or short-term rental. Not only does it create some extra income, but it helps ease Seattle's housing crisis by providing additional rental units.
Listing a backyard cottage on a nightly rental service, such as Airbnb, has the potential to bring a homeowner the most rental income, but managing bookings and turnovers between guests is not an insignificant amount of work, so most homeowners wishing to rent their DADUs will probably opt for long-term rentals.
Other homeowners build backyard cottages not to rent but as housing for family members. They are a way to make inter-generational living possible. An elderly parent could move into a DADU, or adult children seeking to build a home in Seattle, but who are priced out of the expensive real estate market, could build on their parents' lot.
Still other homeowners design their backyard cottages as an extension of their home's living space, either for guests, hobbies, or other uses.
Some homeowners wishing to downsize may even move into a newly constructed backyard cottage and rent out their main house.
We converted an unused, dilapidated backyard workshop into a DADU that the clients use as a long-term rental unit. Check out more of this conversion here - Greenwood DADU
Here is a summary of some of the new DADU rules for Seattle's single-family zones. Consult a design professional before assuming your DADU is buildable, but you can use the 2019 Seattle backyard cottage rules summary below to quickly check the feasibility of your project.
The minimum lot size required for a backyard cottage is 3,200 square feet in single-family zones. (In the past, you had to have at least a 4,000-square-foot-lot.) The minimum lot width is 25 feet.
The maximum size of the backyard cottage is now 1,000 square feet of floor area in single-family zones, up from 800 square feet. Parking and up to 35 square feet of bicycle storage space is not counted toward this size limit.
Height limits are based on two main factors: the width of your lot and the style of your roof. Lots less than 30 feet wide allow a base structure height of 14 feet, while lots wider than 50 feet allow a base height of up to 18 feet. In addition, you are allowed additional height for your roof, which varies depending on the style of your roof and the width of your lot. A pitched (gable) roof can extend an additional 3 to 7 feet above the base structure height, while a shed or butterfly roof can extend only 3 or 4 feet above.
| Lot less than 30' wide | Lot 30'-40' wide | Lot 40'-50' wide | Lot 50' wide or more | |
| Pitched roof | 17' | 23' | 23' | 25' |
| Shed or butterfly roof | 17' | 20' | 22' | 22' |
Note that the city adds 2 feet of potential "bonus" height for super-insulated or green roofs and 4 feet for railings if you have a rooftop deck.
DADUs cannot be built in front yards, so only side yard/rear yard setbacks apply. In general, you need 5 feet of space between the cottage and your lot lines and from other structures. If your lot borders a back alley, you can build right up to it. If you have a corner lot, your setback is 10 feet.
The footprints of your main house and any accessory structures can cover only a limited percentage of your total lot.
| Lot size | Maximum lot coverage |
| Less than 5,000 square feet | 1,000 square feet plus 15 percent of lot area |
| 5,000 square feet or more | 35 percent of lot area |
If the back of your property abuts an alley, you get a bit of a break; the city calculates your lot area from the center-line of the alley.
Check with a knowledgeable architect or designer to confirm your unique situation, but here are some examples of what Seattle counts toward maximum lot coverage:
Included in lot coverage calculation:
Exempted from lot coverage calculation:
See also: Lot Coverage, Height, Yard, and Garage Standards for Homes in Single Family Zones [Seattle Department of Construction & Inspections]
Your backyard cottage can take up only 40 percent of your required rear yard area, plus 20 percent more if no exceptional trees or trees larger than 2 feet in diameter are removed.
You get another break here if the back of your property abuts an alley. You can add half the width of the alley to your lot depth in the calculator above.
If your rear yard is bigger than the required minimum area, you're in luck! You can use the 40% to 60% of the required rear yard area, as calculated above, plus any leftover rear yard area not taken up by your main home and other structures.
Dedicated off street parking for backyard cottages is no longer required. However, the city still requires the main residence to have one off-street parking spot that does not sit inside of a setback.
The owner of the property need not live in the main house or the backyard cottage under the new regulations.
In addition to your main home, you can build up to one detached backyard cottage and one attached in-law apartment or two attached in-law apartments.
For many homeowners, the cost to build a DADU will be offset by steady rental income and an increase in their home's value. With that said, building a DADU is quite expensive and is a large investment. To find out more about the cost to build a DADU, check out our Backyard Cottage Pricing Guide for the most up-to-date pricing information!
A lot goes into creating a backyard cottage that perfectly fits your needs today and can adapt to new uses in the future. Our staff of interior designers and architects can help make your vision a reality, and our team of professional lead carpenters can keep the building process smooth and on schedule. Our construction cue is filling up. Please feel free to reach out today to discuss your goals and the feasibility of construction. We would be happy to answer your questions and share our ideas.
Note: We make no claims or warranties as to the completeness or accuracy of the information on this page. We encourage you to confirm all information you read here and consult a design professional. Any action you take based on the information on this website is strictly at your own risk.