Seattle ADU Requirements (kind of like a MIL Mother In Law, but Not)

Real Estate Agent with Team Leader/ Investor for Brand New Keller Williams North Seattle Office

Thinking about converting your basement or attic into rental income?  Seattle has a great policy for allowing accessory dwelling units (ADU) on residential properties.  Ballard real estateThis is a great way to be able to rent out part of your home and allow someone to legally live in a separate part of your home while you live there. Additionally, you can live in the ADU yourself if you choose and the renter can live in the main home.  It doesn't matter as long as you stay within the city's guidelines for establishing an attached accessory dwelling unit.

Seattle ADU rules, rquirements & guidelines (you have to meet all of them although there are some variances allowed if applied for properly): 

1. the home has to be occupied by one or more owners and the owner has to have at least a 50% interest in the property.  Additionally, the owner occupant has to live there for at least 6 months a year.

2. Unless all residents in both units are related to each other, the limit is eight people in the entire structure.

3. One off street parking space must be provided for ADU( you can apply for a waiver on this one).

4. Only one ADU for each home (this includes backyard cottage or ADU).

5. ADU can only be 1000 square feet although there are some more details for getting around this if the ADU is all on one floor and structure was in existence prior to 6/1/1999.

6. Usually only one entrance can be located on front or side street locations. Ther eare some exceptions.

7.  Window for sleeping room has to be a certain size - according to city literature:

"In sleeping rooms located in buildings constructed after Aug. 10, 1972, or in rooms converted or established for sleeping purposes after August 10, 1972, there shall be at least one operable window or exterior door approved for emergency escape or rescue. The window or door must be operable from the inside. All emergency escape windows shall have a minimum net clear opening of 5.7 square feet (grade floor openings allowed to be 5 square feet), a minimum net clear openable height dimension of 24 inches, and a minimum net clear openable width dimension of 20 inches. The window must have a finished sill height not more than 44 inches above the floor. The sill height may be measured from the top of a constructed step with a riser of not more than 7 inches."

 8. The ADU has to meet all current Seattle residential standards for building, mechanical, electrical, and energy codes.  (Look for good ceiling height and egress. )

9. Electrical boxes either have to be located in common areas or in the areas for the units they serve.

(Make sure and check out the city's application here:

 Seattle Mother In Law, Backyard Cottage, ADU... 

 These are all different!  An ADU is different than a mother in law (MIL) apartment which is a separate residence within a home and allows you to rent out the MIL apartment without having to live in the other part of your home. Backyard Cottages are also different.  An ADU us the best way to live in your home and have either legal separate living quarters fro your nanny or housekeeper or make extra income to offset your mortgage. 

Are you interested in finding a   Seattle home that you can convert part of the space into an ADU?  Seattle is ADU friendly and Seattle real estate has opportunities for just this type of set up!

Posted by



Courtney Cooper

Seattle Realtor

Cooper Jacobs Real Estate Group powered by Keller Williams Downtown Seattle | 206-850-8841 

(Seattle real estate - search all MLS listings from all companies), (or look for them for sale: Seattle Houseboats), (Green Lake Blog), (Queen Anne Blog), (Magnolia Neighborhood Blog),,,

About Me: 

Seattle real estate has been a huge part of my life for well over a decade since I began my career in real estate,but also before that time when I was in the process of purchasing my own first home.  Buying your first home can be quite overwhelming,but I have managed to help many first time home buyers along the way.

Move up Seattle buyers and other types of specialized purchasing is a great passion of mine!  I love Seattle houseboats and you can find me down on the docks of Lake Union and Portage Bay several times a week.   Other aspects of Seattle real estate that I adore include Queen Anne Real Estate,Wallingford Real EstateBallard Real EstateGreen Lake Real EstateLaurelhurst Real EstateMagnolia Real Estate,and Seattle Waterfront Real Estate

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Fred Carver Personal Real Estate Corporation
RE/MAX Camosun Victoria BC Real Estate - Victoria, BC
Accredited Real Estate Consultant

Hi Courtney.....We call them Mortgage Helpers here, but not all municipalities allow what we call basement suites, many turn a blind eye, others want an annual tax for a secondary suite. the Good news lender accept the income to help with qualifying for a mortgage.

HAPPY HALLOWEEN Fred on Halloween

Oct 29, 2009 05:47 PM #1
Courtney Cooper
Team Leader/ Investor for Brand New Keller Williams North Seattle Office - Seattle, WA

Mortagge helpers.... I like that:)  Very true!  Seattle is pretty friendly to ADUs which is nice.

Oct 30, 2009 02:40 AM #2
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