Techniques for Reducing the Potential Impact of a Flood

The FEMA publication, “Homeowners Guide to Retrofitting: Six Ways To Protect Your House From Flooding”, provides information that will help determine if a house is a candidate for retrofitting and describes six retrofitting methods that protect homes from flooding. The Affordable Mitigation for Affordable Housing educational program recommends four of the six methods, which are listed below and described in detail within this section:

• Elevations

• Wet floodproofing

• Dry floodproofing

• Levee and flood wall

Elevations

Electrical system components are easily damaged by floodwater. Even if they are inundated for only short periods of time, they will most likely have to be replaced. Another problem with electrical systems created by floods is the potential for fires caused by short circuits.

Raising electrical system components above BFE helps avoid those problems. Also, having an undamaged operating electrical system after a flood will help expedite clean up and repairs, and allow the occupants to return to their homes with shorter delays. In an existing house, this work will require the removal of some interior wall sheathing (drywall, for example). If you are repairing a flood-damaged house or building a new house, elevating the electrical system will be easier.

Below are some tips for elevating electrical panels and outlets:

• The main electric panel (fuses or circuit breakers) should be at least 12” above the projected flood elevation for your home. The panel board height is regulated by code, and all electrical work should be done by a licensed electrician.

• Elevate electric service lines (at the point they enter your home) at least 12 inches above the projected flood elevation.

• Elevate all electric outlets, switches, light sockets, baseboard heaters, and wiring at least 12” above the projected flood elevation for your home.

• In areas that could get wet, connect all receptacles to a ground fault interrupter (GFI) circuit or outlets to avoid the risk of shock or electrocution. Have this electrical wiring done by a licensed electrician.

Raising the electrical service panel, meter, and all of the outlets, switches, and wiring in a 1,000-square-foot, single-floor house could cost about $1,500 to $3,000. If this work is performed during the repair of a damaged house the cost may be lower.

Wet Floodproofing

Wet floodproofing allows water to enter a home in a way that minimizes damage to the structure and its contents. Wet floodproofing techniques make uninhabited parts of a home resistant to flood damage when water is allowed to enter during flooding. Wet floodproofing is less costly than other retrofits, as no additional land is required. In addition, wet floodproofing does not affect the appearance of the house. It is important to note that wet floodproofing cannot be used in V zones. This section includes some of the considerations for wet floodproofing, and Table C below highlights the key advantages and disadvantages of wet floodproofing.

Flood Vents

Flood vents create permanent openings in the foundation walls. Flood vents allow water to move through the foundation of the house freely, thereby reducing water pressure applied to the structure. This retrofit requires at least 2 vents on 2 different walls. The size of the vents must be 1 square inch of opening per 1 square foot of enclosed ground level first floor area. For example, a 1,000-square foot-single story house would require 1,000 square inches (7 square feet) of vents. Each vent is estimated to retail for approximately $175.

Elevating Appliances

For protection against shallow floodwaters, appliances, such as washers and dryers, can be elevated on masonry or pressure-treated lumber at least 12” above the projected flood elevation. Other options include moving the washer and dryer to a higher floor, or building a concrete or masonry floodwall at least 12” above the projected food elevation around the appliances. The cost of a floodwall will depend on the construction materials used and the wall’s height and length. A 3-foot-high, 35-feet-long wall would cost about $1,000.

Elevating the Furnace, Water Heater, and Air Conditioning Units

Air conditioning units, furnaces and water heaters also can be placed on masonry blocks or concrete at least 12” above the projected flood elevation, moved inside a floodwall, or moved to a higher floor. Another option for a furnace that operates horizontally is to suspend it from ceiling joists if the joists are strong enough to hold the weight.

Installing a draft-down furnace in the attic may be an option if allowed by local building codes. In addition, some heating vents can be located above the projected flood elevation. Having your furnace and water heater moved to a higher floor or to the attic can cost approximately $1,500, depending on the complexity of the work.

Anchoring a Fuel Tank

A fuel tank can tip over or float in a flood, causing fuel to spill or catch fire. Cleaning up a house that has been inundated with floodwaters containing fuel oil can be extremely difficult and costly. Fuel tanks should be securely anchored to the floor or ground. It is important to make sure the tank’s vents and fill line openings are above projected flood levels.

Propane tanks are often the property of the propane company. If the company owns the tank, you will need written permission to anchor them. Ask whether the company will anchor the tank for you. Anchoring a 1,000-gallon fuel tank to a concrete base can cost about $300 to $500. Using straps and ground anchors can cost about $300.

Plumbing

Preventing floodwater or sewage back up from entering the home is important. For preventing floodwater from entering the home, a” floating floor drain plug” at the current first floor drain location should be installed. That way if the floor drain backs up, the float will rise and seal the drain. To prevent sewage back from entering the home, have a licensed plumber install an interior or exterior backflow valve.

Backflow valves are available in a variety of designs. A gate valve provides one of the strongest seals, but must be operated by hand, so the effectiveness of a gate valve will depend on how much warning you have of impending flooding. Among the simpler valves are flap or check valves, which open to allow flow out of the house but close when the flow reverses. These valves operate automatically but do not provide as strong a seal as a gate valve.

Having a plumber or contractor install a backflow valve will cost approximately $400 to $600 for a combined gate/flap valve or approximately $300 to $500 for a flap valve. These figures include rough estimates of the cost of excavation and backfilling.

Flood Resistant Materials

When using wetfloodproofing techniques, it is critical to use flood resistant materials, which include:

• Concrete

• Stone

• Masonry block

• Ceramic and clay tile

• Pressure-treated lumber

• Epoxy paints

• Metal

It is also important to remove any non-flood resistant materials from the potential flood areas. Those materials include:

• Drywall

• Insulation

• Carpeting

• Non-pressure-treated lumber

• Plywood

Dry Floodproofing

Dry floodproofing consists of sealing a home to prevent floodwater from entering. Dry floodproofing can only be used in the A zone, when expected flooding is less than 3 feet deep and the expected duration of flooding is short. The advantages of dry floodproofing are that it may be less costly than other methods, and it does not require additional land.

Dry Floodproofing involves making the walls impermeable to floodwaters; closing doors, windows, and vents with permanent or removable shields; and closing sewer and water lines with valves. The advantages and disadvantages of dry floodproofing are summarized in Table D below.

Exterior Walls

Even in areas where floodwaters are less than 2 feet deep, a house can be severely damaged if water reaches the interior. The damage to walls and floors can be expensive to repair, and the house may be uninhabitable while repairs are underway.

One method of waterproofing the exterior wall is to apply an asphalt coating to the existing wall, covering the asphalt coating with polyethylene film and installing a new brick veneer to cover the plastic and asphalt. Be sure to bring the sealant and plastic down along the slab and several inches below ground level.

If you have a contractor add a waterproof brick veneer structure to your house, you can expect to pay about $10 per square foot of wall. For example, a 3-foot-high brick veneer on a house measuring 180 feet around, would equal 540 square feet and would cost about $5,400. This figure does not include the cost of sealing doors and other openings or extending the foundation.

Levee and Floodwall

Levee and floodwall protection means constructing barriers to prevent floodwater from entering a home. This process involves building a levee out of a compacted earthen structure or engineering a floodwall structure of concrete or masonry. The advantages of building levees or floodwalls are that there are no significant changes to the home; the home can be occupied during construction of the levee or floodwall, and this protection method reduces the risk of flood damage. Table E below highlights the advantages and disadvantages of levee and floodwall protection.