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1. What is the 100-year flood plain?

The 100-year floodplain, also known as the Special Flood Hazard Area (SFHA), is an area of land that has been determined by the Federal Emergency Management Agency (FEMA) as having a 1% chance of flooding in any given year. The floodplain is composed of a flood way and a flood fringe. The flood way is typically determined to be the channel of a river or stream and the overbank areas adjacent to the channel. The flood fringe is the area to either side of the flood way that is subject to flooding but conveys little or no flow. In Winnetka, there are two sources of floodplain: the Skokie River and Lake Michigan.  

2. What regulations must be followed for construction within and adjacent to the flood plain?

The Village of Winnetka’s Flood Hazard Protection Ordinance is Chapter 15.68 in the Municipal Code. In addition, the Metropolitan Water Reclamation District (MWRD) Watershed Management Ordinance (WMO) contains floodplain regulations that all municipalities within Cook County are required comply. 

3. What is the Base Flood Elevation (BFE)?

The Base Flood Elevation (BFE) is the elevation below which areas are at risk of flooding for the 100-year flood event.  The current BFE for the 100-year flood event for the Skokie River is 625.3 NAVD 1988, which is generally consistent throughout the limits of Winnetka (between Hill Road and the northern Village Limits), but does vary south of Hill Road. The BFE and Flood Zone Designation for Lake Michigan have recently undergone revisions. Based upon the results of the Great Lakes Coastal Flood Study, FEMA has revised the BFE for Lake Michigan to a variable BFE ranging from 587 to 594 NAVD 1988, depending upon where the property is situated along the lake front in Winnetka. The Flood Zone Designation will also change from Zone AE to Zone VE, which is a coastal flood zone that takes into account wave action. 

Any grade that is equal to or below this elevation is considered in the floodplain, when tributary to that floodplain.  This elevation is referenced from the North American Vertical Datum (NAVD) of 1988.  

4. What is the Flood Protection Elevation (FPE)?

The Flood Protection Elevation (FPE) is the elevation to which any structures within the floodplain are required to be protected. In compliance with the MWRD WMO, the Flood Protection Elevation is two feet above the BFE.  Within the Village of Winnetka, the FPE for the Skokie River is 627.3 NAVD 1988.  

5. When is my house considered in the flood plain?

If any grade adjacent to the foundation of the house is at or below the BFE, the entire house is determined to be in the floodplain and must comply with the Village’s Flood Hazard Protection Ordinance.  

In addition, the MWRD’s WMO stipulates that if a home is within 100’ of the mapped BFE, any permit applicant who is wanting to construct a new home or make substantial improvements to an existing home must prove, by means of a topographic survey, that all grades adjacent to the home are above the BFE (by at least 0.1 feet) to be considered outside of the floodplain.

6. My property was never in the flood plain before, why is it in the flood plain now?

FEMA completed two re-mappings of Winnetka’s western floodplains, one in November 2000 and one in August 2008, and one remapping of the lake Michigan coastline in September 2021. Due to increased rainfall intensities and various other topographic changes, the BFE rose approximately 9”, as part of the 2000 remapping. In addition, the 2008 remapping and modernization more accurately reflects the floodplain limits north of Willow Road. The 2021 remapping of Lake Michigan takes into effect wave action and wave velocities. 

7. When do I need to buy flood insurance?

Anyone in Winnetka can purchase flood insurance, even if the property (a building and/or its contents) is not located within the floodplain. However, if your property is located within the 100-year floodplain, and you have a federally backed loan or mortgage on the property, you are required by law to purchase flood insurance. 

8. Can I build in the flood plain?

Yes, new construction is permitted in the floodplain in accordance with the Village of Winnetka’s Flood Hazard Protection Ordinance, Sections 15.68.050.G and 15.68.080.  

Construction of a new home or structure with a basement may be permitted in the floodplain if a Letter of Map Revision – Fill (LOMR-F) is first obtained from FEMA. The LOMR-F can be obtained if engineered fill has been placed and compacted on the site to create a clay building pad for the home.  All work must be done in accordance with the Village’s Flood Hazard Protection Ordinance.  A LOMR-F, removes that portion of the property that was filled from the floodplain, thereby allowing a home to be constructed with an engineered basement. Otherwise, if site constraints do not allow for a LOMR-F, a home with a floodable crawlspace (no basement) may be constructed.  The details of the design requirements are outlined in Section 15.68.050.G and 15.68.080 of the Flood Hazard Protection Ordinance.

Compensatory storage must be provided to offset any fill that is placed in the floodplain, under any circumstance.  Compensatory storage must equal a minimum of 1.1 x Fill volume.

9. Are there any restrictions for construction for homes adjacent to the 100-year flood plain?

The MWRD’s WMO requires that new home construction and/or substantial improvements to existing homes need to prove, by means of a certified topographic survey, prepared by either an Illinois Registered Land Surveyor or Professional Engineer, that the existing/new home and/or improvements are above the BFE by at least 0.10 feet.  

 Regardless, if you are considering constructing a new home that is within 100’ of the BFE, the following design criteria must be met:

• The top of foundation (and any opening in those foundations) must be at or above the FPE.  
• It must also be demonstrated that the building and foundation below the BFE are reasonably safe from flooding, per design standard requirements in FEMA Technical Bulletin 10-01, and the Village’s Flood Hazard Protection Ordinance, Section 15.68.050.G.   

These requirements include:

• Providing integrally cast window wells with the foundation wall;
• Maintaining the top of foundation at a minimum elevation of the FPE; 
• The foundation must be constructed of poured concrete without seams/joints; 
• All attendant utilities, including the air conditioning units must be set to at least the FPE; and 
• The foundation elements must be designed and certified to withstand any applied hydrostatic pressures. 

10. What are the criteria for being able to construct a new home with a basement in the 100-year flood plain?

There are two main criteria:

First, there is the Minimum Average Lot Grade Requirement:

Per the Village’s flood hazard protection ordinance, the Average Lot Grade must be greater than the Minimum Average Lot Grade.  That means that if you took the average lot grade, which is the average of the existing elevations taken at the intersection of the setback lines, it must be a greater value than the Minimum Average Lot Grade.  The Minimum Average Lot Grade Equations is as follows:

Minimum Average Lot Grade: (627.3-2) - [(total required side yard permitted by Zoning – 12’) x 0.0833] 
It is recommended that the prospective builder consult with a Professional Civil Engineer to investigate the logistics of constructing a new home with a basement on a lot.

Second, there are clay pad construction restrictions which may directly affect the size of the home, and are as follows: 

• The lowest finished grade for the top of the clay pad must be at least to the FPE, and extend at least 10’ beyond the exterior face of the home’s foundation wall, around the entire perimeter of the home, before dropping to the BFE;
• The BFE must extend at least 20’ beyond the exterior face of the home’s foundation wall, around the entire perimeter of the home, before dropping below the BFE;
• The basement floor elevation can be no deeper than 5’ below the BFE;
• The elevation of the lowest opening in the basement wall (i.e. window wells, access ways…) must be at or above the FPE.  This means that all window wells/access ways and the like, must be integrally constructed with the foundation wall, with no joints or seams;

There are additional criteria that must be met, but they are more material related.

11. Can I make improvements to my existing home in the flood plain?

Yes, as long as the Flood Hazard Protection Ordinance criteria are met.  Improvements to an existing structure can be classified as either a Non-Substantial Improvement or a Substantial Improvement.  A Substantial Improvement to an existing structure will require that the entire structure be brought into compliance with the Village’s Flood Hazard Protection Ordinance, whereby the lowest level of the structure and all attendant utilities must be elevated to the Flood Protection Elevation (FPE), which is 2’ above the Base Flood Elevation (BFE).  These requirements are summarized, as follows:

For any improvements to the home (including an attached garage), to be considered a Non-Substantial Improvement, the total cost of the improvements must be less than 50% of the current market value of the structure, excluding the land, and must be calculated cumulatively over the remaining life of the structure, beginning with any permit issued on or after May 2014. 

If additions to an existing structure increases the building’s footprint by more than 20%, the addition must be elevated to the FPE. This increase in footprint is cumulated in aggregate, beginning with any permit issued on or after May 2019.  

To determine the current market value, you can either use the Cook County’s Assessor’s information, or get a certified appraisal, using the depreciated value of the structure.  The Village cannot take the replacement value of the structure, as it does not accurately reflect the market value.  

Cook County’s Assessor’s website can be found here.  You can search by address or property PIN.  To obtain the adjusted assessed value for the structure, take the assessed value for the structure and multiply by 10.  Then, to determine the substantial improvement value threshold, divide that number by 2.

Once the 50% cost of improvement threshold has been met or exceeded, it is considered a substantial improvement, and as noted above, the entire home and attendant utilities need to be elevated such that the lowest floor is at or above the Flood Protection Elevation (BFE + 2’).  This would most likely mean that you would need to fill in the basement and potentially jack up the rest of the home.  As part of the permitting submittal, copies of the executed contracts that outline the entire scope of work, and any subcontracts that may be necessary, must be submitted for review.

12. What is compensatory storage?

Compensatory storage is an artificially excavated, storage volume within the 100-year floodplain that is required to offset the loss of natural storage capacity caused by the placement of fill, structures, or other materials above the existing natural grade. Compensatory storage must meet the following requirements (For the full description of the requirements, please see the Section 15.68 of the Village’s Flood Hazard Protection Ordinance and the MWRD WMO, Article 6):

• Equal to at least 1.1 the volume of flood storage lost below the BFE;
• Be operational prior to the placement of any fill;
• Must be able to drain without the use of a pump or other mechanical means;
• Must be freely flowing into and out of the storage facility (no underground compensatory storage unless at least one end of the pipe/system is exposed to the invert of the pipe/system).

13. How can I find out if my property is located within the flood plain?

Call Emily Grimm at 847-716-3532: as the Flood Plain Manager in the Village of Winnetka, she will be able to read the Flood Insurance Rate Maps and give an approximation of whether your property is within a flood zone. However, in order to make an exact determination, a topographic survey would need to be obtained by either an Illinois Licensed Land Surveyor or Professional Engineer.

Also, the Flood Insurance Rate Maps (FIRMs) can be found in the FEMA map center. However, in order to make an exact determination, a topographic survey or elevation certificate would need to be obtained by either an Illinois Licensed Land Surveyor or Professional Engineer.