Zoning, building permits and septic rules in Mukilteo, Washington

Mukilteo’s own rules

• Building permitLimited

  Construction inside Mukilteo city limits.

  • Listed exemptions remain subject to applicable safety standards and may require environmental or land-use permit review.
  • A residential accessory structure exemption is limited to structures 200 square feet or smaller meeting all listed conditions.

  residential accessory-structure exemption threshold: <= 200 square feet (Must be one-story, detached, nonhabitable, unheated, and meet the additional conditions in § 15.04.040(A)(1).)

  “Exemptions From Building Permits. The following do not require a building permit but are still subject to applicable safety standards and may require environmental or land use permit review:”

• Building code adoptedAdopted (with conditions)

  Buildings and construction inside Mukilteo city limits.

  • The City adopts the listed codes subject to City-specific amendments.
  • The adopted residential code includes Appendix Q (Tiny Houses).

  International Residential Code edition: 2021 (Together with state amendments in WAC Chapter 51-51, including Appendix Q.)

  “The 2021 Edition of the International Residential Code, as published by the ICC, together with state amendments as set forth in Chapter 51-51 WAC including:”

• Local zoningPresent (with conditions)

  Land inside Mukilteo city limits.

  • Title 17 zoning and its district, use, and development standards apply.

  “In order to implement the comprehensive plan, to provide for protection of property and to preserve the health, safety and welfare of the community, the city is divided into the following classes of districts:”

• Living in an RVTemporary only (with conditions)

  Trailers or mobile homes used for living purposes in residential zoning districts inside Mukilteo city limits.

  • The cumulative two-week limit does not apply when the temporary use is associated with active construction of a residence.

  maximum cumulative period: <= 2 weeks per calendar year (Unless associated with active construction of a residence.)

  “The temporary use of trailers or mobile homes for living purposes in residential zoning district may not exceed a cumulative total of two weeks each calendar year unless it is associated with active construction of a residence.”

• Camping on your landLimited

  Temporary encampments inside Mukilteo city limits.

  • Temporary encampments must comply with Chapter 17.78.

  “Temporary encampments must comply with Chapter 17.78, Homeless Temporary Encampments.”

• Accessory dwellingsLimited

  Accessory dwelling units on single-family residential lots inside Mukilteo city limits.

  • No more than two ADUs are allowed on a single-family residential lot.
  • ADUs are not allowed in cottage housing developments.
  • Maximum habitable floor area is 1,000 square feet.

  maximum ADUs: <= 2 ADUs per single-family residential lot (Not allowed in cottage housing developments.) · maximum habitable floor area: <= 1000 square feet

  “Maximum Number of Units. A maximum of two accessory dwelling units are allowed on a single-family residential lot. Accessory dwelling units are not allowed in cottage housing developments.”

• Driveway accessLimited

  Residential lots with accessory dwelling units inside Mukilteo city limits.

  • The Director may approve an exception based on unusual circumstances.
  • No new frontage improvements are required for installation of an ADU.

  driveways per residential lot: 1 driveway (Unless the Director approves an exception based on unusual circumstances.)

  “Access. Each residential lot is limited to one driveway unless the director approves an exception based on unusual circumstances. No new frontage improvements are required for the installation of an ADU.”

• Building in a floodplainLimited

  Development proposals in special flood-hazard areas inside Mukilteo city limits.

  • All studies must be prepared by a Washington-licensed registered professional engineer.
  • At the City's option, studies/plans may be reviewed by a City-retained consultant at applicant expense.

  “All development proposals in special flood hazard areas shall be subject to the provisions of Chapter 15.12, Flood Damage Prevention. All studies shall be prepared by a registered professional engineer licensed in the state of Washington. At the city's option, the studies/plans may be reviewed by a consultant retained by the city at the applicant's expense.”

• Permit feesVariable (with conditions)

  City building-code permits inside Mukilteo city limits.

  • Fees are established by City Council resolution.

  “Fees shall be as set forth by city council resolution.”

• Permit processPublished (with conditions)

  City permit applications and resubmittals inside Mukilteo city limits.

  • Applications and materials are submitted digitally through the linked portal; the City provides forms, checklists, and resources.

  “We've gone digital! Please submit permit applications and materials at the link above. Access application forms, submittal checklists, and other resources.”

Rules another office applies inside Mukilteo

Mukilteo does not set these itself; the county, a health district or the state does, and they apply to every address inside its limits.

• Minimum lot sizeDistrict specific (with conditions)

  RD 9.6 and RD 9.6(S) zoning districts inside Mukilteo city limits.

  • Bulk standards apply to newly created lots and lot-line adjustments.
  • The City may approve a site-specific development agreement that modifies development standards subject to the stated statutory procedure and conditions.

  minimum lot area: 9600 square feet (RD 9.6 and RD 9.6(S).)

  “Lot Bulk Matrix. Zone | Minimum Lot Area | Maximum Density | Minimum Lot Width | Minimum Lot Depth RD 12.5/12.5(S) | 12,500 sf | Each lot may have 1 duplex or 1 single-family dwelling with up to 2 ADUs | 50' for internal lots 60' for corner lots | 85' RD 9.6/9.6(S) | 9,600 sf”

• Who permits septicLocal (with conditions)

  Septic permits for land inside Mukilteo city limits.

  • The City's permit page directs applicants to Snohomish Health District for septic permits.

  “Septic, Well and Public Pool Permits: Snohomish Health District”

Still unanswered

We looked and could not find an official answer yet. Silence is not permission; ask Mukilteo or Snohomish County directly.

• Owner-builder exemption — Owner-built dwellings inside Mukilteo city limits.
• Inspections — Building work inside Mukilteo city limits.
• Certificate of occupancy — New or altered dwellings inside Mukilteo city limits.
• Minimum dwelling size — Primary single-family dwellings inside Mukilteo city limits.
• Tiny homes — Tiny homes used as dwellings inside Mukilteo city limits.

Each answer was extracted from an official source and independently re-checked against that source by a second reviewer. That is an evidence check, not legal advice. Rules change; confirm with the authority before you buy or build.

Off-grid gear

Going off-grid in Mukilteo means bringing your own water and power. The kit we’d start with:

• Water Crystal Quest Filter any source — well, rain, or creek — to drinking-clean.
• Power Bluetti Solar generators and home battery backup for living off the grid.
• Septic Soil percolation test kit Run your own perc test before paying an engineer — the first thing a septic office asks about.
• Water Well water test kit Bacteria, nitrates, hardness — know what the well on a parcel is really pumping.

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