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FAQs - Community Planning & Development
Home Businesses

Q: What is a home business?

A: A home business is an office or use that is secondary to the residential use of the property. However, your home business cannot alter the residential character of the neighborhood, there can be no external evidence of its operation, and the proposed use conforms to certain conditions.

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Q: How can I get a permit?


A home business is a permitted use in all residential zoning districts, so a separate land use approval is not required for a home business that complies with the conditions contained in ULDC Section 19.05.010 (A) (5). You must have a current Mercer Island business license from the Mercer Island Finance Department.

Building permits are required for adult family homes and family child daycare homes. All other businesses require a permit unless all of the following are met:

  • The business is an office, mercantile, food prep for off-site consumption, personal care salon (or similar use, when approved by the Building Official).
  • The business is conducted primarily by occupants of the dwelling unit.
  • The business use is secondary to the use for dwelling purposes.
  • The business gross floor area does not exceed 500 square feet.
  • Alterations are not made to the building that would require a permit. See Our Building Permits, Codes and Plan Review page.

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Q: What conditions are required to operate a home business?


  • The home business shall not involve the external alteration of any structure.
  • Only those persons who reside on the premises and one other person who does not reside on the premises shall be permitted to engage in the business. (Provided, if this limitation conflicts with the minimum licensing requirements for Child Day Care Centers, the number of employees who do not reside on the premises may be increased to meet the minimum staff-child ratios set out in WAC388-150-190.)
  • There shall be no exterior storage or display of materials, and no sign advertising the occupation located on the premises.
  • No offensive noise, vibration, smoke, dust, heat or glare; or unusual or excessive traffic to and from the premises shall be produced or generated by the business.
  • The business shall not involve the use of more than 25% of the gross floor area of the primary residence calculated by excluding any attached garage from the gross floor area. However, the garage area may be used for the home business, provided such use does not exceed 25 percent of the gross floor area as calculated above.
  • The home business will not be permitted if it generates vehicle traffic that cannot be accommodated by the lot’s pre-existing off-street parking.

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    Q: Are some home businesses not allowed in residential districts?


    Yes, a home business may not provide healthcare services, personal services, automobile repairs; serve as a restaurant, commercial stable, kennel or place of instruction of more than three students at a time. A bed and breakfast is not permitted without a conditional use permit as provided for in ULDC 19.02.010(C)(7).

    For further information, please contact the Finance Department or the Development Service Group¡¯s Customer Service Team 206-275-7606.

    Note: This information is summarized from Title 19 of the Mercer Island Municipal Code, "Unified Land Development Code¡± and is provided for quick reference only. To determine exact requirements, and for other development regulations affecting a parcel or lot, Title 19 should be consulted.

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