Docks

Residential Docks and alterations

The Mercer Island Community Planning and Development department’s Building team has the following guidelines and expectations for permit applications for residential dock repairs, alterations, and new construction.

When preparing the construction documents and supplemental information to apply for a building permit involving docks, please determine which of the following categories of work applies to the scope and review the specific guidance. In order to assist city staff during review, it may also be helpful to clarify in your construction documents which of these categories your project falls under in a scoping statement on the drawings.

Many if not all dock development in the city of Mercer Island are governed by the Shoreline Management plan. Please review and provide design compliance and apply for the required permits.

The guidelines below are intended to assist applicants by anticipating the likely thresholds for requiring design and are broken down into three categories of project scope.

  1. For repairs and re‐decking of existing docks without any reconfiguration of the dock shape.
  2. For reconfiguration of a dock shape to accommodate any new use.
  3. For new dock construction, or for complete dock replacement.

    * Additional Permits or Content may be Required:

    • Potable Water Installation: Please obtain a plumbing permit for RPBA installation
    • Lake Water Irrigation: Please obtain Landuse Shoreline Exemption permitting
    • Electrical: Please obtain an electrical Permit

#1. Repairs and re‐decking of existing docks without any reconfiguration of the dock shape

  1. The scope of work should be identified prior to permit application. These permits cannot be issued with a vague description of the work. If up to 50% of the piles or 50% of the framing is to be replaced as part of the project, the specific components should be identified on a framing plan. If this scope of work changes as damage is discovered during construction, a revised plan should be submitted.
  2. Gravity calculations should be provided for any framing members being replaced, and the size, location, and material of the new framing should be identified on plan. Depending on the configuration of the dock, the appropriate live load may be 40 psf for piers or 60 psf, the same as applies to residential decks.
  3. All details for re‐attachment of framing should be provided where repairs are made.
  4. Pile repair is a common need for these projects. It will be very important to identify the need and purpose for any work done to piles, as it will affect review.
    • In cases where the existing pile is suitable for re‐use from lake bed to pile cap, but voluntary protection against decay is being installed, this should be identified as "decay prevention," "protection," or other similar notes.
    • In cases where the pile is being modified or cut below the waterline to competent material and spliced with new material, an engineered solution needs to be provided for the pile splice. This doesn't have to be specific to the project (a generic stamped letter for the splice of a 12" pile will work), but the pile splice detail needs to be submitted along with an engineer.
    • In cases where a pile is replaced in‐kind, complete specifications for the pile and its installation should be included (material, size, embedment, etc)

#2. Reconfiguration of a dock shape to accommodate any new use

  1. If a dock is being modified or reconfigured, the new uses should be identified in the documents. (e.g. if the dock is being extended to provide additional draft for mooring, or extended for access to a lake‐bed supported boat lift, this type of use should be noted).
  2. All docks with new structure being proposed to accommodate the new use or configuration should be accompanied by gravity calculations for the new framing members, pile calculations, and details for all connections.
  3. Moorage of recreational boats 25 feet and less is considered incidental and will not require specific engineering consideration.
  4. If the new use for a dock is to accommodate (or appears to accommodate) vessels exceeding 25 feet, a professional engineer should evaluate the proposal to a recognized standard for fixed, permanent moorages of boats. Examples of this are UFC 4‐152‐07 “Design: Small Craft Berthing Facilities,” NAVFAC Design Manual 26, or ASCE Manual 50 "Planning and Design Guidelines for Small Craft Harbors." The City of Mercer Island has not adopted a code which includes dock design, so it will be the responsibility of your engineer to determine the appropriate standard. Design criteria for building construction contained in ASCE 7 are not appropriate for most docks mooring vessels over 25 feet.
  5. In cases where a dock appears to accommodate a vessel larger than 25 feet, but there is no intent to do so, the Building Official may require that the drawings and the dock itself be labeled with the capacity that the engineer has considered in the design, or with "No moorage of vessels longer than 25 feet."

#3. Dock construction, or for complete dock replacement:

  1. All new dock designs should be accompanied by complete framing plans, gravity calculations for the framing members, pile calculations, and details for all connections.
  2. Moorage of recreational boats 25 feet and less is considered incidental and will not require specific engineering consideration.
  3. If the new dock accommodates (or appears to accommodate) vessels exceeding 25 feet, a professional engineer should evaluate the proposal to a recognized standard for fixed moorages of boats. Examples of this are UFC 4‐152‐07 “Design: Small Craft Berthing Facilities,” NAVFAC Design Manual 26, or ASCE Manual 50 "Planning and Design Guidelines for Small Craft Harbors." The City of Mercer Island has not adopted a code which includes dock design, so it will be the responsibility of your engineer to determine the appropriate standard. Design criteria for building construction contained in ASCE 7 are not appropriate for most docks mooring vessels over 25 feet.
  4. In cases where a proposed dock appears to accommodate a vessel larger than 25 feet, but there is no intent to do so, the Building Official may require that the drawings and the dock itself be labeled with the capacity that a professional engineer has considered in the design, or with "No moorage of vessels longer than 25 feet."
     

     

Construction Documents Requirements

The following items should be merged into a single PDF file for submittal. This package will become your approved drawings set.  Please bookmark each sheet in the plan set (i.e.: A1.1- Site Plan) prior to submittal.  Click here to read our tip sheet on How to Bookmark Plans.

  1. Site Plan
  2. Framing Plans/ Structural Framing Plans
  3. Cross Sections
  4. Additional details as necessary for the construction of the proposed scope.

    *Addition details as necessary for the construction of the proposed scope

How to Apply

Upload submittal documents to the Mercer Island Permit Submittal Portal.  

 

  • If an Intake Screening has been requested, staff will schedule the Intake Screening, and will email you the screening results.
    1. If the submittal is incomplete, the results will include instructions to address staff comments and resubmit.
    2. If the submittal is complete, it will the be routed for review.

 

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