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=Definition= Wet floodproofing is a method of flood preparation that involves building designs and material choices that allow for the entry of floodwaters into the structure, while minimizing the potential negative impacts and damage caused. This resilience measure should be designed to account for the height of building flood elevations, buoyancy and hydrostatic pressures of flood waters and wave action. Wet floodproofing differs from dry floodproofing in that dry floodproofing measure take steps to prevent the entry of water entirely.

__ Ideally, wet floodproofing measures:  __

• Ensure flood waters may both enter and exit the structure • Ensure flood waters on the interior of the structure rise and fall at the same rate as exterior flood waters • Protect structural elements, objects and materials that are below the DFE from damage and corrosion caused by contact with flood waters • Protect mechanical and service equipment located on the interior or exterior of the structure • Ensure items located in floodable areas below the DFE are secured or moved away from floodable areas

=Issues Addressed= Wet floodproofing addresses the need to accommodate increased flood risk, and adapt buildings to become more resilient in flooding events. New York City has experienced flash floods, storm surge, storm tide, river flooding, and inland flooding events caused by extreme weather such hurricanes, tornadoes, nor’easters and high precipitation events.

New York City’s more than 600 miles of coastline means a large volume of the built environment exists within 10 feet of average sea level. Global sea level rise is a slow, yet steady, process, which incrementally increases the chances for various types of flooding that impact coastal areas. The New York City Panel on Climate Change has stated that “as sea level rises, coastal flooding associated with storms will very likely increase in intensity, frequency, and duration.”

Increased precipitation is another projected factor in future climate change models. Volume of annual precipitation may increase by as much as 10% by the 2080’s. These combinations of risk factors has resulted in the adjustment of Federal flood hazard mapping to show increased flood risk assessments.

Special Initiative for Rebuilding and Resiliency (SIRR)
Wet floodproofing falls within the scope of SIRR goals for buildings: Wet floodproofing methods address Iniative 7 of the Buildings chapter “Encourage existing buildings in the 100-year floodplain to adopt flood resiliency measure through an incentive program and targeted requirements”. Dozens of DDC buildings exist within the SIRR flood zones. Public buildings have the opportunity to set precedent and stand as examples for surrounding private structures. Buildings that are retrofitted to adopt wet floodproofing measures should consider the potential to publicize the measures and create signage to demonstrate proper application of the measure to citizens.
 * Strengthen new and rebuilt structure to meet the highest resiliency standards
 * Retrofit as many existing buildings as possible to improve resiliency

=Considerations= Wet floodproofing may only be an appropriate resilience method for certain buildings and uses. Acceptable situations include flooded areas that are used for non-residential uses including basements, sub-floor crawlspaces, parking garages, storage areas, and some commercial areas.

It is important to note that wet floodproofing does not guarantee protection from high hydrostatic pressures caused by fast-moving flood water, wave action, and any debris that is carried by those flood waters. Considerations for these types of events may require the use of flood barriers, green infrastructure, shoreline protections, levees, or flood walls to combat effects.

Wet flood proofing measures should be aligned with a building’s Emergency Plan. “Pumping out the wet floodproofed basement too quickly can result in structural damage. If the outside earth is still saturated, the outside of the wall may be under greater pressure than the inside of the wall, which can result in damage to the basement wall.

Construction or remodeling methods should also allow for the structure, including wall and floor cavities or systems, to drain and dry. Water and vapors must be able to escape and dry in at least one direction, preferably two.

Equipment (furnace, water heater, washer, dryer, water softening equipment, etc.) should be relocated to a higher floor or elevated above the flood protection elevation. Utilities and electrical panels should be relocated to a floor above the flood protection elevation or to the attic.”

“Flood-resistant materials are those that can be inundated by flood waters with little or no damage. They include such materials as concrete, stone, masonry block, ceramic, and clay tile. pressure-treated and naturally decay-resistant lumber, epoxy paints and metals. In addition to resisting damage from flood waters, these materials are relatively easy to clean after flood waters have receded.” In a cost comparison of floodproofing methods, it is often the case that wet floodproofing measures are less costly than dry floodproofing measures.

Code Compliance
“Requirements for flood opening sizes, location, number and other characteristics are primarily governed by NFIP regulations. The major requirements are outlined below, but the FEMA document that provides extensive details about meeting flood opening regulations is Technical Bulletin 1-2008, Openings in Foundation Walls and Walls of Enclosures. The American Society of Civil Engineers (ASCE) has developed the standard Flood Resistant Design and Construction (ASCE 24). This standard applies to buildings and site developments proposed in flood hazard areas. It is also referenced by the International Building Code. ASCE 24 Section 2.6.2.2 contains installation and design criteria for engineered openings. Local ordinances also refer to these three documents as a basis of their own floodproofing ordinances. The major requirements are as follows: Openings must be in multiple walls. In order to allow water to flow freely in and out of the building, each enclosed area is required to have a minimum of two openings on exterior walls, located below the BFE. They should be installed on at least two sides of the enclosed area to allow for more even filling and draining of floodwater. If possible the openings should be reasonably distributed around the perimeter, unless there is a special justification for putting them on just two sides, e.g. in townhouses or buildings set into sloping sites. The International Building Code (by reference to ASCE 24) requires a “minimum of two openings on different sides of each enclosed area.” Wall location. The NFIP's definition of an enclosure is any portion below an elevated building that is fully shut in by four rigid walls. Basements are not allowed in Special Flood Hazard Areas. To avoid having an enclosure classified as a basement, the entire length of one wall must have its inside grade higher than or equal to the outside grade for that wall. This would qualify the enclosure as a walkout basement. Opening location. The bottom of the opening must be no more than one foot above the grade that is immediately under the opening, either the adjacent ground level, or the interior grade, whichever is higher. The lower wall will experience hydrostatic pressure first, so most of the openings should be there. This alleviates the initial force of the water and then provides quick drainage when water begins to recede. In practice, most communities require additional height, or “freeboard,” and insurance premiums will be substantially reduced by additional freeboard. (See sidebar.) Materials. All materials below the BFE must be made of flood resistant material such as stainless steel or specially treated flood resistant lumber. Opening size. ASCE 24 is referenced in all regulations, and it requires that a 3-inch sphere should be able to pass through the flood opening. This is to ensure that grills and louvers don't interfere with the passage of debris, or become so blocked that they are ineffective. It is well known that no flood water is crystal clear. Debris is a fact of flood, and can be devastating in itself.



Screening. ICC building codes require that openings be screened to prevent the entry of insects, rodents, birds, etc. Commercially available grates, louvers and grills are available for this function. However, as just mentioned, the louvers and screens can't interfere with the equalization of the water levels, and they must be selected to minimize potential blockage by debris. Any opening that includes a cover is an unacceptable measure according to FEMA TB-1. Screens also affect the calculation of the required net opening area, discussed next. Net open area. The NFIP's standard for non-engineered openings requires one (1) square inch of net open area for every square foot of enclosed area. Any part of a screen, grate or louver that impedes entry will be subtracted from the net opening area. Non-engineered openings also do not meet the standards if they are likely to be closed during the winter, as many air vents are. In fact, any air vent intended to be used as a flood opening is required to be disabled in the open position, so that it physically cannot be closed. Other commonly used air vent devices will not qualify as acceptable flood openings, such as devices with detachable covers, or temperature-controlled vents that will shut automatically when waters rise around the foundation. Windows will not qualify as flood vents. Often window glass will remain in place even when a wall is dislodged from its foundation. Garage doors do not qualify in themselves, as they could be disabled in a power outage and would require human intervention even if useable. However, some code-compliant automatic flood vents can be installed in garage doors. Automatic Operation. Wet floodproofing measures that satisfy NFIP requirements must be automatic. That means that the system must be strictly passive, operating with no human interaction required (e.g., opening or closing of vents).” Floodproofing Non-Residential Buildings" []

=Applications= FEMA documented a properly applied use of commercial wet floodproofing measures in Key West, Florida at a restaurant located within beach front property at The Duval Beach Club. The restaurant’s owner was interested in reducing the risk of future damage from storm surge and hurricanes after enduring major damage during Hurricanes Rita and Wilma 2005, it was hit by Hurricanes Rita and Wilma. “Appliances and furniture in the restaurant were installed for quick removal when storms threaten. They can be disconnected, rolled out, and stored in containers away from the beach. The walls for the restrooms, which are perpendicular to the ocean, are poured concrete and anchored to the concrete slab. The walls facing the ocean are designed to break away when inundated by storm surge. Another mitigation measure was to elevate the electrical system. Wiring runs from the top of each wall down to the outlets, which are elevated 42 inches from the floor. Extra wiring coiled at the top of the walls can be pulled down for use after flooded outlets are cleaned and damaged wiring removed. The roof of the restaurant has a hip design and is built to withstand the winds of a Category 5 hurricane. A hip roof is somewhat of a pyramid in shape, sloping upward from all four sides of a building. Wind flows better over this type of roof than other types, such as gable designs, and is therefore recommended in hurricane-prone regions. Because a gable roof has overhangs, high winds can create an upward force that pries the roof off the wall. The restaurant’s hip roof is sheathed with ¾-inch marine plywood to resist moisture and covered with aluminum-zinc alloy coated steel sheeting. The eaves hang low to the ground, and the supports and roof structure are connected with hurricane clips for added strength. The design provides a continuous load path from the slab on one side of the building through the top roof members and down to the slab on the other side of the building. In other words, the pieces of the building are tied together from the top down so that the entire structure resists wind forces.”

=Related Reports= =                              References                               =
 * A Stronger, More Resilient New York