Guide to Floodproofing

This Guide was prepared by the Illinois Association for Floodplain and Stormwater Management to provide general guidance on protecting a building from surface water, sewer backup and leaky basement walls. It is appropriate for most flood and drainage problems in Illinois.

This Guide encourages people subject to flooding to help themselves. Here’s where to start:

1. Check with your community’s building, planning or engineering department on the extent of flooding at your property: 
 

Where does the water come from?

Are you in a mapped floodplain or floodway?

How bad has it been the past? 

How bad could it be? (Remember, the next flood can be worse than the last one.)

What is an appropriate flood protection level? (How high should you prepare for?)

In most subdivisions, lots were laid out and built so water would flow away from the building and along property lines to the street, storm sewer, or ditch. Fences, railroad ties, landscaping and regrading can block this flow. So do construction projects in the ditches or the floodplain. Therefore, most communities have regulations on building and development designed to prevent new construction from making flooding and drainage problems worse.
 

Every piece of trash can contribute to flooding. Even grass clippings and branches can accumulate, plug channels, or kill vegetation and contribute to erosion. If your property is next to a ditch or storage basin, please do your part and keep the banks clear of debris.

Do not dump or throw anything into the ditches or basins. Dumping in ditches, storage basins, and wetlands is a violation of local codes.

Always check with your building department before you build on, fill, alter, or regrade your property. A permit is needed to ensure that such projects do not cause problems on other properties.

The most secure flood protection measure is to get your building out of the path of flooding. Where flooding is deep (e.g., over 4 feet over the first floor) or repetitive, it may make more sense to move the building than to elevate or floodproof it and leave your family exposed to a destructive or repeated hazard.

Smaller houses on crawlspaces are the easiest to move or elevate. The cost goes up with larger buildings, buildings on slab or with fireplaces, and masonry walls. For expert guidance, check house & building moving and raising in the Yellow Pages.

There may be some financial assistance programs to relocate damaged buildings or even to acquire and demolish them. Check with your building, planning or community development department on possible sources of help.
 

Short of removing it from the floodplain, the best way to protect a house from surface flooding is to raise it above the flood level. The area below the flood level is either filled in or left with openings to allow floodwaters to flow under the building, causing little or no damage. Elevation is required by law whenever a new house is constructed in a floodplain.

Because floodwaters in most of Illinois are usually not very deep, the appearance of the elevated house is similar to that of a house on a two- or three-foot crawlspace. If the house is raised two feet, the front door would be three steps higher than before.

Adequate crawlspace openings are required, but may be camouflaged with landscaping.
 

Barriers keep surface floodwaters from reaching a building. A barrier can be built of dirt or soil (berm) or concrete or steel (floodwall). The standard design for earthen berms is three horizontal feet for each vertical foot (3:1 slope). As a result, you should plan on needing an area six feet wide (at a minimum) for each foot in height.

Depending on how porous your ground is, if floodwaters will stay up for more than an hour or two, your barrier will need to handle leaks, seepage of water underneath, and rainwater that falls inside the perimeter. You will need a sump and/or drain to collect the internal groundwater and surface water. A pump and pipe is also needed to pump the internal drainage over the barrier.

A berm or floodwall should be as far from the building as possible to reduce the threat of seepage and hydrostatic pressure. However, it must not interfere with drainage along your property line. Where the house is close to the property line, you may need to backfill to make a berm next to the wall as illustrated above. Don’t forget: a permit is needed for filling or regrading a yard. There may be restrictions on bringing fill onto your site if it blocks the flow of flooding or displaces floodwater storage areas.

Precautions Barriers can only be built so high. They can be overtopped by a flood higher than expected. Earthen berms are susceptible to erosion from rain and floodwaters if they are not properly sloped and covered with grass and maintained. Don’t plant trees or shrubs on a berm (their roots can cause leaks). Barriers can settle over time, lowering their protection levels.

Some barriers have openings for driveways and sidewalks. Closing these openings is dependent on someone being available and strong enough to put the closure in place. You also need to account for water in the sewer lines that may back up under the barrier and flood inside your house.
 

This term covers several techniques for sealing up a building to ensure that floodwaters cannot get inside it. All areas below the flood protection level are made watertight. Walls are coated with waterproofing compounds or plastic sheeting. Openings (doors, windows, and vents) are closed, either permanently, with removable shields, or with sandbags. Many dry floodproofed buildings do not look any different from those that have not been modified.

Dry floodproofing is only appropriate for buildings on concrete slab floors (without basements) and with no cracks. To ensure that the slab is watertight and sound, an engineering analysis is recommended.

The maximum flood protection level for dry floodproofing is two feet above the slab. Deeper water will put pressure on your walls and slab floor that they are not built to withstand. It is smarter to let deeper water into your house than to risk loosing your walls or floor.

Precautions: It is very tempting for the owner of a dry floodproofed building to try to keep the flood out if floodwaters get deeper than two or three feet. This can result in collapsed walls, buckled floors, and danger to the occupants.

Dry floodproofing is only appropriate for buildings with slab on grade foundations. It is difficult to waterproof a crawl space to protect it from underseepage. Basements should not be dry floodproofed to protect them from surface flooding because of the water pressure on the walls and floors.

Many commercial waterproofing compounds are made to protect wood from rain, but they will not withstand the pressures of standing water. Some deteriorate over time, so check with the supplier to be sure the waterproofing compound is appropriate for sealing your basement walls from water. Installing closures and seals over doors and windows requires enough warning and having someone at the building who knows what to do.
 

Wet floodproofing means letting the water in and removing everything that could be damaged by a flood. There are several ways to modify a building so that floodwaters are allowed inside, but minimal damage is done to the building and its contents. These techniques range from moving a few valuable items to rebuilding the floodprone area.

In the latter case, structural components below the flood level are replaced with materials that are not subject to water damage. For example, concrete block walls are used instead of wooden studs and gypsum wallboard. The furnace, water heater, and laundry facilities are permanently relocated to a higher floor. Another approach is to raise these items on blocks or platforms where the flooding is not deep.

Wet floodproofing is not feasible for one-story houses because the flooded areas are the living areas. However, many people wet floodproof their basements, garages, and accessory buildings simply by relocating all hard-to-move valuables, such as heavy furniture and electrical outlets. Light or moveable items, like lawn furniture and bicycles, can be moved if there is enough warning. Fuse and electric breaker boxes should be located so you can safely turn the power off to the circuits serving floodprone areas.

Another approach is to wet floodproof a crawlspace. If your crawlspace has a furnace in it or is used for storage, these items could be moved to the first or second floor. Vents should be placed on the foundation walls to ensure that floodwaters can get into the crawlspace to equalize water pressure.

Wet floodproofing has one advantage over the other approaches:  no matter how little you do, you will reduce your damages. Thousands of dollars in damage can be prevented by simply moving furniture and electrical appliances out of a basement.

Precautions: Moving contents is dependent on adequate warning and the presence of someone who knows what to do. Flooding a basement or garage where there is electricity, paint, gasoline, pesticides, or other hazardous materials creates a safety hazard. There will still be a need for cleanup, with its accompanying health problems. Moving water lines, furnaces, or electric service boxes requires a building permit from the Building Department.
 

Basement flooding caused by saturated ground can be corrected by installing a footing drain around the foundation to collect groundwater and direct it to a sump. When the sump fills, water is pumped out, usually onto the ground away from the building. Depending on local conditions, the drain and pumping system may have to handle large volumes of water.

Note: Your floor drain may or may not be connected to the sanitary sewer line.

If the pump is blocked with debris, gets overloaded, or there is a loss of power, the system designed to keep groundwater out of your basement can act as a conduit to bring water in. You can prevent sump flooding by doing one or more of these floodproofing projects:

Clean the pump intake to remove blockages,

Install a larger sump pump,

Add a second or third pump,

Connect the pump to a backup source of electricity, such as a battery system or generator,

Disconnect the downspouts from the footing drain,

Redirect the downspouts and sump pump outfall farther away from the house, and/or

Run the sump pump outfall above ground level or use a check valve to prevent back flow.

Groundwater can seep into your basement around pipes or if there are cracks in the walls or floor. This may be difficult to determine if the walls have been covered with paneling or other finishing. The best way to deal with a groundwater problem is to waterproof the walls and relieve the water pressure through a footing drain system and sump (see previous section).

Cracks can be repaired and the walls can be waterproofed from inside or outside. Waterproofing on the outside is more effective because groundwater pressure forces the sealer into the foundation. The best technique is to dig a ditch around the basement wall so that you can apply a commercial sealant to the exterior walls. This can be done by a handyperson (many home maintenance manuals have instructions for this) or a commercial waterproofing company.

Precautions: Waterproofing alone is only recommended for groundwater problems. Surface water will put much more pressure on the building’s walls and can even break them. If the building is affected by surface flooding, you should also install a barrier as explained on page 9.

This type of work is hidden. A sloppy job may not show up for several years. Be sure to ask the waterproofing supplier or company to provide references of buildings in your area that have used their material or technique. Call their past customers to confirm the quality of their work.
 

The illustration shows the sewer arrangements for a typical house with a basement. The sanitary sewer line drains toilet waste, laundry tubs, and (sometimes) the basement floor drain to the sanitary sewer main in the street. Clean stormwater and groundwater is handled by downspouts, footing drains, and sump pumps.

Often basement flooding is caused by these two sewer systems being interconnected. Some houses have the downspouts, footing drain, and/or the sump pump connected to the sanitary sewer service. During a heavy rain, stormwater enters the sanitary sewers, causing backups into one house and overloading the main lines, contributing to backups in other houses.

Sewer backups can also be caused by events not related to storms or flooding. Individual service lines can be plugged by grease, waste, tree roots, breaks in the pipe, or saturated ground. Proper main tenance, like pouring tree root killer down the toilet each year, can prevent most of these problems. The sewer mains can also be plugged by the same causes as well as vandalism or illegal placement of items in manholes. These problems can be fixed by the owner or your community, depending on where the stoppage occurs.

The next four sections of this Guide focus on protection measures that deal with sanitary sewer backup that occurs when the sewer main is overloaded and backs up through the sanitary service line into the house. There are four ways to stop sewer backup: floor drain plug, floor drain standpipe, overhead sewer, and backup valve. Each of these measures work for buildings with basements or below-grade floors.

Sewer Backup Prevention — Floor Drain Plug: The simplest way to stop sewer backup is to plug the opening where it first occurs. This is at the floor drain, the sanitary sewer system’s lowest opening in the house. Commercial plugs are available that can be placed in the floor drain below the grate. Bolts on metal end pieces are tightened, causing a rubber gasket to expand and seal the plug in the pipe.

The advantage of a plug is its low cost and ease of installation. A standard floor drain plug can be purchased at most local hardware stores for $5-10.

A plug stops water from flowing in either direction. Therefore, if the laundry tub overflows or other spillage occurs, it will stay in the basement unless the plug is removed. Because of this, it may be best to leave the plug out under normal circumstances and put it in place only during heavy rains.

One variation is a plug with a float. It allows water to drain out of the basement (see illustration, top left). When the sewer backs up, the float rises and plugs the drain. A float plug permanently installed will not interfere with the floor drain’s normal operation.

Precautions: A plug left in the floor drain may contribute to a wet basement if spillage cannot drain out. Float plugs are known to have been jammed open by a small amount of debris.

A floor drain plug does not stop backup from coming out of the next lower opening, like a laundry tub or basement toilet. Sealing the base of the toilet to the floor will protect you until the water backs up higher than the top of the bowl.

A plug does not tell you if there is a problem in your sewer service line. If the plug is not tight enough, pressure can eject it. In older houses, the sewer lines under the basement floor may be clay tile. A buildup of pressure can break them. In newer houses, they are cast iron under the floor and less likely to break.

Sewer Backup Prevention — Standpipe: A standpipe is an inexpensive alternative to a floor drain plug. A “donut” with metal end pieces and a rubber gasket in the middle is placed in the floor drain. A length of pipe is placed in the “donut hole.” Bolts are tightened and the metal end pieces squeeze the gasket to make a tight seal on both the floor drain and the pipe. The “donut” can be purchased for about $10. A three-foot length of pipe costs less than $5.

When the sewer backs up, the water stays in the pipe. Water pressure cannot build up to blow a standpipe (if properly installed) out of the floor drain. The system works unless the backup is so deep that it goes over the top of the pipe.

One advantage of the standpipe over the floor drain plug is that the overflow acts as a safety valve. Flooding in the basement equalizes water pressure on the walls and floor, minimizing the chance of a cracked floor from broken pipes underneath.

Precautions: A standpipe left in the floor drain may contribute to a wet basement if spillage cannot drain out. A standpipe only protects up to its height, normally three feet. Deeper flooding will flow over the top. (A taller standpipe is not recommended because it can result in too much water pressure on your pipes.)

A standpipe does not stop backup from coming out of the next lower opening, such as a laundry tub or toilet in the basement. Sealing the base of the toilet to the floor will protect you until the water backs up higher than the top of the bowl.

Because water pressure depends on the height of water in the pipes, a standpipe does not reduce the pressure in the pipes. Because the pressure in the pipes is the same with a standpipe or a plug, standpipes and plugs are only recommended for buildings with cast iron sewer lines underneath the floor.

Sewer Backup Prevention — Overhead Sewer: An overhead sewer acts like a standpipe but without the problems. A sump is installed under the basement floor to intercept sewage flowing from basement fixtures and the basement floor drain. An ejector pump in the sump pushes sewage up above the flood level. From there it can drain by gravity into the sewer service line. Plumbing fixtures on the first floor continue to drain by gravity to the service line.

It is unlikely that the sewers will back up above ground level. If water does go higher, a check valve in the pipe from the ejector pump keeps it in the pipes. Backed up sewage is enclosed in the sewer pipes so there is no worry about overflowing laundry tubs or basement toilets.

Precautions: The ejector pump requires maintenance and electricity to work properly. The basement is disrupted during construction. The contractor may have to run the overhead pipes through one or more basement rooms, although often they can be camouflaged. This work requires a licensed plumber and a permit from your building department.

During a power outage, the ejector pump won’t work. But this only limits the use of the facilities in the basement that need the pump. The upstairs plumbing still works and the sewer is still prevented from backing up.

Although more dependable than a standpipe, an overhead sewer is more expensive. A plumbing contractor must reconstruct the pipes in the basement and install the ejector pump. It typically costs $2,000 - $5,000.

Sewer Backup Prevention — Backup Valve: A backup valve stops the water in the sewer pipes. Older versions of this approach were located in the basement and relied on gravity to close the valve. If debris got caught in the flapper, the valve did not close tight. Because of its unreliability, valves were discouraged and even prohibited in some communities.

A newer “balanced valve” has corrected these design shortcomings. A system of counterweights keeps it open all the time so debris won’t catch and clog it. When the sewer backs up, instead of relying on gravity, floats force the valve closed. It is usually installed in a manhole in the yard so there is less disruption during construction and no concerns over breaking the pipes under the basement floor.

As with overhead sewers, a valve is fully automatic. It can even work when there is surface flooding. The owner can still use the sanitary sewers during flooding as long as there is power to run the ejector pump, which forces wastewater into the sewer line when the valve is closed.

Precautions: The ejector pump and the valve require maintenance. This work requires a licensed plumber and a permit from your building department.

The cost this type of backup valve is comparable to the cost of an overhead sewer, in the $3,000 - $5,000 range.
 

Basements and the lower floors of split levels can be protected from surface water by construction of low walls around stairwells or using backfill. First, a waterproofing compound is applied to the walls. Walls are built up around the window wells (don’t block basement windows that are needed for emergency exits). An earthen berm can be filled against the side of the house.

A subsurface drain and one or two correctly sized sump pumps are a must. The drains and pumps can keep up with the seepage before it gets through the berm and reaches your house.

The secret is to not let floodwaters touch the house. If water on the surface of the ground gets up against the house, it probably will seep down the gap between the basement walls and the surrounding soil. This will greatly increase the amount of water pressure against the basement walls.

Sump pumps cannot keep up with surface water. If you have sandy or permeable soil, you should consult an engineer or soils expert to ensure that the berm will extend far enough away from the walls. Don’t forget: filling or grading in your yard requires a permit.

Precautions: The berm can only be built so high. It can be overtopped by a flood higher than expected. Being made of earth, it is susceptible to erosion from rain and floodwaters if not properly sloped and covered with grass and maintained. A berm can settle over time, lowering its protection level. The small floodwalls can crack, weaken, and lose their watertight seal.

You also need to account for water in the sewer lines, footing drain and sump pump outfall. They may carry water under the barrier and flood inside your house. See the sections on sewer backup prevention on pages 8 - 11.
 

Flood insurance is highly recommended. Even if the last storm or flood missed you or you have done some flood proofing, the next flood could be worse. Most home owners insurance policies do not cover property for flood damage.

Almost every community in Illinois with a flood problem participates in the National Flood Insurance Program. Local insurance agents can sell a flood insurance policy under rules and rates set by the Federal government. Any agent can sell a policy and all agents must charge the same rates.

Any house can be covered by a flood insurance policy. Detached garages and accessory buildings are covered under the policy for the lot’s main building. Separate coverage can be obtained for the building’s structure and for its contents (except for money, valuable papers, and the like). The structure generally includes everything that stays with a house when it is sold, including the furnace, cabinets, built-in appliances, and wall-to-wall carpeting.

There is no coverage for things outside the house, like the driveway and landscaping. Renters can buy contents coverage, even if the owner does not buy structural coverage on the building.

Don’t wait for the next flood to buy insurance protection. There is a 30 day waiting period before National Flood Insurance coverage takes effect. Contact your insurance agent for more information on rates and coverage.

Some people have purchased flood insurance because it was required by the bank when they got a mortgage or home improvement loan. Usually these policies just cover the building’s structure and not the contents. During the kind of flooding that happens in most of Illinois, there is usually more damage to the furniture and contents than there is to the structure.

Many insurance policies will only pay to repair the damage incurred. If your damage is severe you may have additional costs to bring your building up to current codes. Flood insurance now covers these costs (up to $15,000) when there is a flood. Check your home owner’s insurance policy to see if it has this coverage for fire, wind or other hazard.

Precautions: Flood insurance does not cover contents in a basement or the finished structural parts of a basement, such as paneling or wall to wall carpeting. Flood insurance only covers damage when there is a general condition of surface flooding in the area.

Several insurance companies have sump pump failure or sewer backup coverage that can be added to a homeowner’s insurance policy. Each company has different amounts of coverage, exclusions, deductibles, and arrangements. Most are riders that cost extra and exclude damage from surface flooding that would be covered by a National Flood Insurance policy. Cost varies from nothing up to about $75 for a rider on your homeowner’s insurance premium.
 

Many of the flood protection measures discussed in this guide can be built or installed by the homeowner.  However, some work requires a licensed plumber and some can be more involved than the handy person may want to do. Here are some suggestions on dealing with contractors.

If you have been satisfied with work done by local contractors, try them first. If they cannot help you, ask them for recommendations. If you must hire a contractor you do not know, talk to several contractors before you sign anything.  Reputable contractors agree that you should take the following steps:

Check on the firm’s reputation: Home Builder’s Associations can give you names of member companies and can tell you if people have filed complaints against them.

Look out for “special deals”: Be cautions when unfamiliar contractors offer “special deals” after a storm or want to use your home as a “model home.” Ask for complete financial details in writing and for an explanation of any differences from regular prices. Sales are worthwhile and they do exist, but be sure you are getting the services and products you are paying for.

Ask for proof of insurance: Worker’s compensation and general liability insurance are absolutely essential. If the contractor is not insured, you are liable for accidents on your property.

Ask for references: Contractors should be willing to provide names of previous customers. Call some of the customers and ask if they would hire the contractor again.

Ask for a written estimate: Check it for thoroughness. Some contractors may charge a fee for an estimate which is understandable when they have plenty of work to do.

Ask for a contract: The contract should be complete and clearly state all the work and the costs. Never sign a blank contract or one with blank spaces. If a lot of money is involved, it may be worth your while to have the contact reviewed by a lawyer.

Ask for any guarantees in writing: If the contractor provides guarantees, the written statement should include what is guaranteed, who is responsible for the guarantee (the dealer, the contractor, or the manufacturer), what is covered beyond the written guarantee, and its duration.

Obtain a copy of the final signed contract: Once signed, it is binding on both you and the contractor.

Cool off: Do not sign a contract when a salesperson has pressured you. Federal law requires a three-day “cooling off” period for unsolicited door-to-door sales of more than $25. If you want to cancel such a contract within three business days of signing it, send your cancellation by registered mail. Other types of sales may have contracts with varying decision clauses.

Avoid cash payments: Beware if you are asked to pay cash on the spot instead of a check made out to the contracting company. A reasonable down payment is 10-30% of the total cost of the project.

Don’t sign off before the job is finished: Don’t sign completion papers or make the final payment until (1) the work is completed to your satisfaction and (2) the building department has made its final inspections. A reputable contractor will not threaten you or pressure you to sign if the job is not finished.

Get your permits: Most home improvements, filling, fences, and other yard work require a permit from the building department. A permit is needed before the project is started to be sure that it meets code and will not cause a drainage problem on neighboring properties. Permits are always required for any activity taking place in a mapped floodplain area.

Get your inspections: The building department needs to inspect electrical and plumbing lines before the walls are covered with wallboard or paneling. When the project is finished, make sure your contractor calls you and the building department to inspect work before it is covered over. Shoddy work on sewers or basement walls will be hidden from view and you won’t know if there is a problem until the next flood.

Get help: If you are a victim of fraud or have problems with a less than reputable contractor, the Illinois Attorney General Consumer Fraud Hotline at 1-800-243-0618 can tell you what steps to take. The building department would also like to know of problems.
 

Do not walk through flowing water. Drowning is the number-one cause of flood deaths. Currents can be deceptive; six inches of moving water can knock you off your feet. Use a pole or stick to ensure that the ground is still there before you go through an area where the water is not flowing.

Do not drive through a flooded area. More people drown in their cars than anywhere else. Don’t drive around road barriers; the road or bridge may be washed out. A car can float is as little as two feet of water.

Stay away from power lines and electrical wires. The number two flood killer after drowning is electrocution. Electrical current can travel through water. Report downed power lines to your power company.
 

Turn off electricity if your building is flooded. If you don’t know how, call an electrician. Some appliances, such as television sets, can shock you even after they have been unplugged. Don’t use appliances or motors that have gotten wet unless they have been taken apart, cleaned, dried and inspected by a professional.

Watch for animals. Small animals like rats and snakes that have been flooded out of their homes may seek shelter in yours. Use a pole or stick to poke and turn items 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 stairs that have been covered with mud can be very 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 has been thoroughly aired out.

Carbon monoxide exhaust kills. Use a generator or other gasoline-powered machine outdoors. The same goes for camping stoves. Fumes from charcoal are especially deadly, cook with charcoal outdoors.

Clean everything that got wet. Flood waters have picked up sewage and chemicals from roads, farms, factories, and storage buildings. Spoiled food and flooded cosmetics and medicines are health hazards. When in doubt, throw them out.

Take good care of yourself. Wear gloves and boots. Wash your hands frequently during clean up. Recovering from a flood is a big job. It is tough on both the body and spirit and the effects a disaster has on you and your family may last a long time. Keep your eyes open for signs of anxiety, stress, and fatigue in you and your family.
 

This guide is designed to give the reader an overview of things that can be done to protect a property from damage from the type of surface water flooding and sewer backup that faces many locations in Illinois. The information provided is based on careful research and input from experienced professionals. The reader must assume responsibility for adapting this information to fit his or her conditions. This guide is not intended to replace the advice and guidance of an experienced professional who is able to examine a building and assess the needs of the particular situation.