Flood Plain Construction

If you are planning on doing any type of alteration to your home or property, be it an interior renovation, addition, constructing a new or replacement home or garage, shed or other detached auxiliary structure, and/or any type landscaping work that may in any way alter the existing grades on your property, you will need to obtain a permit through the Community Development Department.

For flood plain properties, this permit will need to include a copy of the executed contract for the proposed work; certified calculations and grading plan to address drainage issues as well as compensatory storage requirements; and architectural plans and details that address various flood plain specific construction requirements.

If you have questions regarding the Village’s permitting process, please contact Anita Lichterman at 847-716-3520. For questions regarding the Village’s Flood Plain requirements, contact Emily Grimm at 847-716-3532.

Compensatory Storage

Hazard Protection Regulations preserve the natural storage capacity of the 100-year flood plain, maintaining the volume that the flood plain occupies. Flood Hazard Protection Regulations require that there be no fill placed within the 100-year flood plain without the provision of compensatory storage. Compensatory storage must equal at least 1.1 times the volume of flood storage lost below the Base Flood Elevation (BFE).

Fill

Fill is considered to be any amount of any material that occupies volume between the existing grade and the 100-year base flood elevation. Fill can include:

• Mulch
• Porches
• Raised gardens or patios
• Sheds
• Soil
• Stone
• Timbers
• Any other material or structure, in addition to garages, additions or new homes

The flood plain ordinance has no minimum threshold for what is considered fill, and makes no distinction between various materials, with respect to volume.

When creating or maintaining existing landscaping, you will need to remove 1.1 times the amount of material from your property in conjunction with the placement of any new materials.

Quick Tips - Flood Plain Construction

The Village of Winnetka’s Flood Hazard Protection Regulations, along with the Metropolitan Water Reclamation District’s Watershed Management Ordinance (MWRD’s WMO),requires compliance with certain criteria, depending on the type of construction/development proposed in and within 100 feet of the 100-year flood plain. Permit applicants must comply with the more restrictive of either the Village Flood Hazard Protection Regulations or the MWRD WMO.

The Village has incorporated the WMO in the Flood Hazard Area Protection Regulations, which can be found in Section 15.68 of the Village Code.

Here are some quick reference tips for construction in the flood plain:

• Structures that are located within 100 feet of the 100-year flood plain must comply with the Village’s Flood Hazard Protection Regulations and the MWRD WMO.
  • A WMO Single Family Home-Special Flood Hazard Area Permit Application must be submitted with the building permit application.
  • If the existing/proposed structure is mapped outside of Zone A/AE, but lies within 100 feet of the 100-year BFE, a certified topographic survey must be submitted to prove that the lowest adjacent grade to the existing/proposed structure is at least 0.1 feet above the BFE so that the existing/proposed structure can be considered out of the 100-year flood plain, and therefore, not be restricted to the requirements regarding substantial improvements within the 100-year flood plain
• A topographic survey is needed to make an exact flood plain determinations and to develop a grading plan with compensatory storage calculations
• The total cost of improvements to an existing structure must be less than 50% of the current market value of that structure, excluding the land value, taken cumulatively over the remaining life of the structure
• New construction and substantial improvements must be protected from the flood plain by elevating the structure’s lowest floor a minimum of 2 feet above the BFE
• Compensatory storage is an excavated volume that must be provided to offset any fill placed within the flood plain at a ratio of 1.1 to 1 (cut to fill)
• Compensatory storage must be freely draining, without the use of a pump
• Obtain a permit through the Village for all work within the 100-year flood plain