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Flood Plain Construction and Property Protection

On May 1, 2014, the Metropolitan Water Reclamation District of Greater Chicago (MWRD) became the Storm Water Management Agency for Cook County, adopting their Watershed Management Ordinance (WMO).  All municipalities within Cook County must abide by the new ordinance.  On April 17, 2014, the Village of Winnetka adopted the WMO, and is currently a designated Community, able to review and approve watershed management permit applications on behalf of the MWRD.  In many instances, the WMO is much stricter than the Village’s own ordinances, especially with respect to flood plain construction issues.  The Village must require compliance with the more restrictive of the two jurisdictional agencies’ ordinances.  All requirements set forth herein reflect the more restrictive requirements.  Any permit for a property which lies within 100 feet of the flood plain, must comply with pertinent sections of the WMO.    

When developing property within the flood plain, or within 100 feet of the flood plain, there are certain criteria that must be met prior to the issuance of the building permit.  These criteria vary depending on the type of development proposed.  The different types of development include new construction; substantial improvements, non-substantial improvements to an existing, pre-FIRM (Flood Insurance Rate Map) home; detached auxiliary buildings; and/or any land work that fills or otherwise alters the grade within the flood plain. 

General Permit Requirements

Once the property owner has determined a plan for the property, one of the first steps in developing a property located within the floodplain or adjacent to the flood plain is to obtain a topographic survey.  Second story additions and/or interior remodeling would generally not warrant a topographic survey.  A topographic survey can be prepared either by an Illinois Registered Professional Engineer or Land Surveyor.  A topographic survey provides important land grade and structure elevation information, and is the only definitive method of determining the limits of the 100-year floodplain.  The Flood Insurance Rate Maps and aerial topographic information are not infallible. 

If it has been determined that a home or proposed improvement is located within the 100-year flood plain, or within 100 feet of the 100-year flood plain, the property owner and design professionals must make themselves aware of the requirements set forth in the Village’s Flood Hazard Protection Ordinance as well as the MWRD WMO.  Then, as part of the building permit process, the Village’s Floodplain Development Permit Application must be submitted along with a certified copy of the topographic survey, as required, a copy of either the certified appraisal or adjusted assessed value of the structure and copies of the executed contracts for the proposed improvements.  If the proposed improvement encroaches into the 100-year flood plain, compensatory storage calculations and the related grading plan must be designed and certified by the design professional, typically a Professional Engineer, and submitted with the Building Permit application.  Upon completion of the project, the “as-built” conditions must be certified, to ensure that all engineering and flood plain requirements have been met. It is important to note that any alteration to a structure or land requires a permit from the Community Development Department be issued with approval by the Public Works Engineering Division.  Also, ANY alteration, regrading or filling in the flood plain requires a permit.

New Construction/Substantial Improvements

New construction can be defined as a structure for which the start of construction commenced on or after the effective date of the FIRM affecting the property, and includes any subsequent improvement to such structures.  That means any new home or improvement to an existing home that was constructed on or after the date of the related FIRM, or substantial improvement, must comply with all aspects of the flood protection requirements for buildings.  Therefore, the lowest level of the existing and/or proposed structure and all attendant utilities must be constructed at least 2 feet above the base flood elevation (Flood Protection Elevation - FPE).  This can be accomplished by various means, as outlined in Sections 15.68.050.G, 15.68.080.D and E of the Flood Hazard Protection Ordinance.  Also, improvements to an existing home must be valued at less than 50% of the current market value of the structure, excluding the land, to be considered a non-substantial improvement.  The cost of the improvements will be taken cumulatively from May 1, 2014, forward. 

On May 4, 2001, FEMA published a regulation entitled “National Flood Insurance Program (NFIP): Letter of Map Revision and Letter of Map Revision Based on Fill” and issued Technical Bulletin (TB) 10-01, which became effective on June 4, 2001.  TB 10-01 allows new homes/sites to be engineered to have their lowest level built below the BFE only upon the issuance of a Letter of Map Revision-Fill (LOMR-F) from FEMA.  On August 7, 2001, the Village of Winnetka Council adopted these regulations, amending the Flood Ordinance and on September 11, 2001, FEMA and the Illinois Department of Natural Resources, Office of Water Resources, approved the revision.  However, the WMO does not provide for any amendments that lessen the requirements of TB 10-01 regulations.  Therefore, the clay fill pad must have its finished elevation 2 feet above the BFE (or FPE); must extend a minimum distance of 10 feet beyond the outside face of the foundation to the FPE; must extend a minimum distance of 20 feet beyond the outside face of the foundation to the BFE; must have the basement floor elevation no more than 5 feet below the BFE; and all other criteria set forth in the Flood Ordinance and TB 10-01 must be met, without waivers.  

In accordance FEMA’s TB 10-01, if a property obtains a LOMR-F, the Village can issue a building permit for a new home to be constructed with its lowest level (basement) below the base flood elevation, if specific engineering requirements have been met.  However, basements will only be permitted if the average lot grade is greater to or equal to the minimum average lot grade, as defined in Sections 15.68.020 and 080.E.1.c of the Village’s Flood Ordinance.  Once the placement of engineered fill has been placed, compacted and certified, and all other pre-construction criteria have been designed, certified and met, the property owner can apply to FEMA for a LOMR-F.  Obtaining a LOMR-F from FEMA, technically takes that portion of the property out of the flood plain.  Once a LOMR-F has been obtained, the property owner can then obtain a building permit for the new home construction, as long as all of the site, soils and foundation requirements have been engineered and certified to meet the requirements set forth in the flood ordinance, Section 15.68.050.G.  Upon completion of the construction, the property owner must have all of the design professionals re-certify that all design aspects of the site and structure are in compliance with Flood Hazard Protection Regulations of the Winnetka Village Code (see chapter 15.68), and the structure has been rendered reasonably safe from flooding.

Non-Substantial Improvements to an Existing, Pre-FIRM Home

A non-substantial improvement is defined as any repair or improvement to a structure where the total cost of improvements are less than 50% of the current market value of the structure, excluding the land value.  The current market value can be obtained either by a certified appraisal or by using the assessed valuation of the structure times the multiplier used to convert the assessed value to adjusted assessed value or market value.  The latter method usually provides a lower value for the structure.  Replacement costs used for insurance purposes are not an acceptable method of determining the current market value.  The total cost of improvements must be substantiated with copies of the signed contracts for the proposed work, outlining the entire scope of work.  The cost of the improvements will be taken cumulatively from May 1, 2014, forward.   

A pre-FIRM home is a structure that was built prior to the publication of the FIRM affecting that area.  A non-substantial improvement to an existing pre-FIRM home does not need to comply with the building protection requirements of the flood ordinance, though it is highly recommended.  That means that if the homeowner is willing to assume the additional risk, the lowest level (including the basement) of the improvement can be constructed below the base flood elevation. 

Substantial Damage

It’s common to think substantially damaged merely describes a structure that has sustained a large amount of damage by a flood or other disaster.  In reality, substantial damage is a specific term that applies to a damaged structure in a Special Flood Hazard Area – or floodplain – for which the total cost of repairs is 50 percent or more of the structure’s market value before the disaster occurred, regardless of the cause of damage.  For example, if a structure’s market value before the damage was $200,000 and repairs are estimated to cost $120,000, that structure is “substantially damaged.” Land value is excluded from the determination.

It’s important to know the percentage of structural damage because that information helps property owners decide whether to repair or replace a damaged dwelling, and whether additional work will be needed to comply with local codes and ordinances, such as elevating a house in a floodplain.  The decision about a structure being substantially damaged is made at a local government level, generally by a building official or floodplain manager. 

To calculate substantial damage, the Village official makes a visual inspection of a house, making notes of the impacts to the structure itself and, when possible, to the interior. These notes, coupled with other information such as property valuations and estimated costs to repair, are used to calculate the percentage of flood damage to the structure.  Once a determination on the percentage of damage is made, Village officials then share that information with the property owners.
If a building in a floodplain is determined to be substantially damaged, it must be brought into compliance with local floodplain management regulations:

  • Owners who decide to rebuild may need to elevate their structures, or change them in some other way to comply with those local floodplain regulations and avoid future flood losses.
  • Owners of non-residential structures may need to flood proof their buildings.

For more information about how or why a substantial damage determination was made, property owners should contact the Village of Winnetka Community Development Department and Public Works Department.  ALL property owners should check with the Village’s officials to determine if permits for repair are required BEFORE beginning the work, as there can be serious consequences for not complying with the permitting process.
Property owners who have a flood insurance policy and a substantially damaged building in a Special Flood Hazard Area may be able to use additional funds from their flood insurance policy (up to $30,000) to help defray the costs of elevating, relocating or demolishing a structure.  For more information on this provision – also known as Increased Cost of Compliance – contact your insurance agent.

Auxiliary/Accessory Structures

These types of non-habitable structures (detached garages, sheds, etc.) can be protected against flooding either by elevating the structure or wet flood proofing the structure, in accordance with Section 15.68.080.E.  Wet flood proofing allows flood waters to freely flow through the structure by means of permanent openings provided in the walls of the structure.  All areas below the base flood elevation must be constructed of waterproof materials, as specified in FEMA Technical Bulletin 2-93.  Upon completion of the project, either an engineer or architect must certify the structure as having been properly wet flood proofed.

Compensatory Storage

One requirement that must be met for all types of construction within the flood plain that temporarily or permanently displaces floodplain storage volume is the provision of compensatory storage.  Compensatory storage is the replacement of storage within the floodplain due to filling or the construction of structures as part of a project, and must be provided to preserve the natural storage within the flood plain.  Compensatory storage is required to ensure that development does not result in an increase in flood heights on adjacent properties or an increase in flood flows.   Compensatory storage must equal at least 1.1 times the volume of flood storage lost below the BFE; be operational prior to the placement of fill, structures, or other materials temporarily or permanently placed within the regulatory flood plain; be provided in the immediate vicinity of the flood storage lost, where practicable; drain freely and openly  to the water way. 

Compensatory storage must also be provided incrementally such that all regulatory flood plain storage lost above and below the existing regulatory 10-year flood elevation shall be replaced above and below proposed regulatory 10-year flood elevation, respectively. 

Compensatory storage must be calculated using cross-sections and the “average end method”.  All compensatory storage must be quantified, both before and after construction.  In no case shall the depth of excavation in the front and side yards of the lot exceed 18”, as measured from the previously existing natural grade.  Compensatory storage may be constructed with retaining walls, provided that the retaining walls are not constructed along the sides of the storage area adjacent to a property line.  As part of the permitting process, the Village of Winnetka’s Floodplain Development Permit Application must also be completed and submitted with the building permit application.

Flood Prevention and Protection

All residents can assist the Village of Winnetka’s efforts to prevent and minimize flooding in Winnetka by doing the following:

  • Do not dump or throw anything into ditches, swales, streams or other water conveyance systems.  Dumping or altering grades is in violation with the Village’s ordinance Sections 9.16.020.B.11; 14.04.130.A.1; 15.32.080.G and L; and 15.68.  Even grass clippings, mulch and branches can accumulate and block drainage.  When a drainage-way is obstructed, the water can get displaced onto adjacent properties, potentially causing flooding.
  • If your property is adjacent to a drainage ditch or swale, please do your part and keep the area clear of brush and debris.  The Village of Winnetka has a maintenance program which can help remove major blockages such as downed trees.
  • If you see dumping or debris in ditches, swales or streams, or any filling within the flood plain (including the placement of mulch, soil, timbers, stone, raised gardens or patios, porches, sheds, or any other material or structure, please contact the Public Works Department at 847-716-3568, and the Village can investigate the situation and follow the necessary procedures to handle the violation.  It is important to make the call while the activity is in process.  Otherwise, it can be very difficult to assess whether it is a new or existing condition.
  • If you are considering development on your property, including altering, regrading or filling on your property, a permit will most likely need to be obtained through the Community Development Department, with approval by the Public Works Engineering Division, to ensure that there will be no fill in the flood plain and no adverse drainage impacts on adjacent properties.  Contact the Village of Winnetka Permit Clerk at 847-716-3520 and Engineering at 847-716-3568 to determine whether a permit or approval will be required prior to the work commencing.  Again, it is important to make the call while the activity is in process.  Otherwise, it can be very difficult to assess whether it is a new or existing condition.
  • If you see a building or filling without a Village permit posted, please contact the Community Development and/or Public Works Department at 847-716-3520 or 847-716-3568.

If your home or property is experiencing flooding in the form of ponding water, basement flooding by surface waters, seepage or through the floor drains, there are certain steps you can take to help minimize the problem.

  • If you are experiencing ponding water on your property that is only draining by either evaporation or infiltrating into the ground, you may want to consider installing a storm inlet in the low area on the property to collect storm water and discharge it into the public storm system.  If there is already an existing storm service to the property, and if grade elevations allow for positive drainage and the service is in good condition, then you may be able to tie the inlet into the existing service.  Otherwise, a new storm service can be brought to the site, disconnecting any existing storm service at the main. 
  • If you are experiencing water entering the basement by topping over the window wells or seeping through the foundation wall or footing, providing positive drainage away from the foundation and/or maintaining the foundation’s drain tiles, may help in this case.
  • If you are experiencing water entering through the floor drain in the basement, then, most likely, the sanitary sewer service is the issue, and will need to be investigated.  The first item to investigate, in any case, is to ensure that the storm sewer and sanitary sewer services are not interconnected, in any way.  If it is found that they are, they must be separated, immediately, in accordance with Section 15.24.070 of the Village Code.  Once this issue has been addressed, the Village of Winnetka has a program in place called the Sanitary Sewer Backflow Prevention which assists homeowners in defraying the costs associated with the installation of a sanitary sewer backflow prevention device or overhead sewers.  For additional information about this program, please contact Susan Chen at 847-716-3532 or 

It is important to note that any alteration to a structure or land requires a permit from the Community Development Department be issued with approval by the Public Works Engineering Division.  Also, ANY alteration, regrading or filling in the flood plain requires a permit.

Flood Hazards and Storm Safety

During a storm or flood event, please keep the following safety precautions in mind:

  • Do not walk through flowing water.  Currents can be deceptive; six inches of moving water can knock you off of your feet.  If you have to walk through standing water, use a pole or stick to ensure that the ground is still there.  Often times, the force of the water can lift manhole covers right off of the manhole, and whether the manhole is 2’ deep or 15’ deep, falling into one could cause serious injury or death.
  • Avoid driving through a flooded area, as it could cause not only damage to the vehicle, but could potentially cause injury or loss of life.  Don’t drive around road barriers, as the road or bridge may be washed out or otherwise compromised.
  • Stay away from downed power lines and electrical wires. The number two flood killer after drowning is electrocution.  Electrical current can travel through water.  Report downed power lines, power outages or water outages to 847-501-2531.
  • Look out for small animals, especially snakes.  Small animals that have been flooded out of their homes may seek shelter in yours.  Use a pole or stick to poke and turn things over and scare away small animals.
  • Look before you step. After a flood, the ground and floors are covered with debris including broken bottles and nails.  Floors and stair that have been covered with mud can be slippery.
  • Be alert for gas leaks. Use a flashlight to inspect for damage.  Don’t smoke or use candles, lanterns, or open flames unless you know the gas has been turned off and the area is well ventilated.

The Illinois Drainage Law

The Illinois Drainage Law states that landowners must accept the advantages or inconveniences of drainage that nature places upon their land. One of the most important principles of the Illinois Drainage Law is that owners cannot adversely alter drainage and that owners of lower ground must receive surface water that naturally flows onto it from higher ground. Where the natural flow is from one tract across another tract, the higher land is the dominant tenement, and the lower land is the servient tenement. Owners of dominant tenements have legal rights to have water drain off their lands. Owners of servient tenements have the duty of not obstructing the natural flow.

A landowner has no right to obstruct the flow of surface water. Under Illinois law, the owner of lower land has no right to build a dam, levee, or other artificial structure that will interfere with the drainage of higher land. In fact, the willful and intentional interference by an owner of lower land is considered a petty offense and is punishable by a fine. This is in addition to private lawsuits that the owners of affected properties may file.


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