A flooding having a 1 percent chance of being equaled or exceeded in any given year; also known as the 100-year flood, is called Base Flood

Base Flood Elevation (BFE) is Elevation of the 1-percent flood. This elevation is the basis of the insurance and floodplain management requirements of the National Flood Insurance Program (NFIP).

Crawlspace foundations are typically low masonry perimeter walls with interior piers supporting a wood floor system. These foundations are usually supported by shal¬low footings and are prone to failure caused by erosion or scour.

Design Flood Elevation (DFE) is the elevation of the Design Flood, including wave height relative to the datum specified on a community’s Flood Hazard Map (American Society of Civil Engi¬neers [ASCE 7-02]).

Hydrodynamic forces are the amount of pressure exerted by moving floodwaters on an object, such as a structure. Among these loads are positive frontal pressure against the structure, drag forces along the sides, and suction forces on the downstream side.

National Flood Insurance Program (NFIP) is a Federal program enabling property own¬ers in participating communities to purchase insurance as a protection against flood losses in exchange for State and community floodplain management regulations that reduce future flood damages. Participation in the NFIP is based on an agreement between communities and the Federal Government. If a community adopts and enforces floodplain management regula¬tions to reduce future flood risk to new construction in floodplains, the Federal Government will make flood insurance available within the community as a financial protection against flood losses. This insurance is designed to provide an insurance alternative to disaster assistance to reduce the escalating costs of repairing damage to buildings and their contents caused by floods. The program was created by Congress in 1968 with the passage of the National Flood Insurance Act of 1968.

Figure 1-3; shows the design wind speed map for portions of the Gulf Coast. Contours are 3- second gust wind speeds in miles per hour (meters per second, in the parenthesis) for Exposure Category C, 33 feet height.

Figure 1-13 is the extreme case of:

Open foundations are required in V Zones and recommended in Coastal A Zones. This type of foundation allows water to pass beneath an elevated building through the foundation and reduces lateral flood loads on the structure. Open foundations also have the added benefit of being less susceptible to damage from floodborne debris because debris is less likely to be trapped.

Pile foundations consist of deeply placed vertical piles installed under the elevated structure. The piles support the elevated structure by remaining solidly placed in the soil. Because pile foundations are set deeply, they are inherently more tolerant to erosion and scour. Piles rely pri¬marily on the friction forces that develop between the pile and the surrounding soils (to resist gravity and uplift forces) and the compressive strength of the soils (to resist lateral movement). The soils at the ends of the piles also contribute to resist gravity loads.

A closed foundation is typically constructed using foundation walls, a crawlspace foundation, or a stem wall foundation (usually filled with compacted soil). A closed foundation does not allow water to pass easily through the foundation elements below the elevated building. Thus, these types of foundations are said to obstruct the flow. These foundations also present a large surface area upon which waves and flood forces act; therefore, they are prohibited in V Zones and not recommended for Coastal A Zones. If foundation or crawlspace walls enclose space below the BFE, they must be equipped with openings that allow floodwaters to flow in and out of the area enclosed by the walls (see Figure 2-9 for an isometric view). The entry and exit of floodwater will equalize the water pressure on both sides of the wall and reduce the likelihood of the wall col¬lapsing (see FEMA 99 Fact Sheet No. in Appendix F). Two types of closed foundations are discussed in this manual, perimeter walls and slab-on-grade.

A slab-on-grade foundation is concrete placed directly on-grade (to form the slab) with gen¬erally thickened, reinforced sections around the edges and under loadbearing walls. The slab itself is typically inches thick where not exposed to concentrated loads and 8 to 2 inches thick under loadbearing walls. The thickened portions of slab-on-grade foundations are typi¬cally reinforced with deformed steel bars to provide structural support; the areas not thickened are typically reinforced with welded wire fabrics (WWF) for shrinkage control. While commonly used in residential structures in A Zones, slab-on-grade foundations are prone to erosion and prohibited in V Zones, and are not recommended for Coastal A Zones.

Figure D-7 shows the loading diagram for:

15- Figure D-2, shows paths for wind, live and dead load on a coastal structure.

In coastal areas, a building can be considered a success only if it is capable of resisting damage from coastal hazards and coastal processes over a period of decades. This statement does not imply that a coastal residential building will remain undamaged over its intended lifetime. It means that the impacts of a design-level flood, storm, wind, or erosion event (or series of lesser events with combined impacts equivalent to a design event) will be limited to the following:

• The building foundation must remain intact and functional.
• The envelope (walls, openings, roof, and lowest floor) must remain structurally sound and capable of minimizing penetration by wind, rain, and debris.
• The lowest floor elevation must be sufficient to prevent floodwaters from entering the elevated building envelope during the design event.
• The utility connections (e.g., electricity, water, sewer, natural gas) must remain intact or be restored easily.
• The building must be accessible and usable following a design-level event.
• Any damage to enclosures below the Design Flood Elevation (DFE)* must not result in damage to the foundation, the utility connections, or the elevated portion of the building.

It is recommended that the bottom of the lowest horizontal structural member of V-zone buildings be elevated 1 foot or more above the Base Flood Elevation (BFE),

The following 2 certificates is also required for building a house in the V Zones.
- Lowest Floor Elevation, by a surveyor, engineer, or architect (see Fact Sheet No. 4)
- Breakaway Wall Collapse, by a registered professional engineer or architect (see Fact Sheet No. 27)

Page 205, ( second page of Coastal Building Materials) lists examples of flood-resistant material.

Based on the table in previous question (Page 205). It is recommended that the doors be made of:

Based on table on page 205, it is recommended that the walls and ceilings be made of cement bard, brick, metal, cast stone in waterproof mortar, slate, porcelain, glass, glass block, clay tile, concrete, CMU, pressure treated wood, naturally decay-resistant wood, marine grade plywood or pressure- treated plywood.