In 1983, the City of New York joined the National Flood Insurance Program (NFIP) and adopted the Flood Insurance Rate Maps (FIRMs). The NFIP program is managed by the Federal Emergency Management Administration (FEMA), and has three components: to provide flood insurance, to improve floodplain management, and to develop maps of flood hazard zones. Once the City joined the program, NFIP required the adoption and enforcement of flood resilient Building Code regulations. These provisions are found in Appendix G: Flood-Resistant Construction of the Building Code, and apply within the City’s floodplain.
FIRMs identify buildings in the floodplain and are used for the applicability of Appendix G as well as for calculating flood insurance rates. Within the FIRMs, the floodplain is divided into different areas of risk: the V-Zone, A-Zone and Shaded X Zone. Besides designating the geography and risk profile where flood events are likely to happen the FIRMs also indicate the Base Flood Elevation (BFE), the computed elevation to which floodwater is anticipated to rise during a flood that has a 1% chance of occurring in any given year, also known as the 100-year flood zone.
FIRMs identify buildings in the floodplain and are used for the applicability of Appendix G as well as for calculating flood insurance rates. Within the FIRMs, the floodplain is divided into different areas of risk: the V Zone, A Zone and Shaded X Zone. Besides designating the geography and risk profile where flood events are likely to happen, the FIRMs also indicate the Base Flood Elevation (BFE), which is the computed elevation to which floodwater is anticipated to rise during a flood that has a 1% chance of occurring in any given year.
Flood insurance is required for property owners with federally backed mortgages located within the 1% annual chance floodplain, or the V or A Zones as shown on the FIRM.
The impact of Hurricane Sandy in October 2012 was a brutal reminder that a significant portion of the city is subject to flood risk, even beyond the floodplain delineated by the FIRMs. In 2012, FEMA was already working on an update to the FIRMs and after the storm, new, non-binding flood maps were issued for New York City. These maps, known as the Preliminary Flood Insurance Rate Maps (PFIRMs), reflect the best available information about the city’s flood risks at this time. Compared to the FIRMs, the PFIRMs generally show a larger geography with higher flood elevations. The PFIRMs were adopted on January 31, 2013, by Appendix G of the Building Code, and is used in combination with the FIRMs to designate risk.
The PFIRMs are updated maps and, like the FIRMs, designate the 1% annual chance floodplain, dividing the floodplain into four different areas of risk –V Zone, Coastal A Zone, A Zone and Shaded X Zone. The V and Coastal A Zones are vulnerable to waves, while the A zone is an area that is vulnerable to flooding but not wave damage. FEMA flood maps also show the Shaded X Zone, which is also known as the 0.2% annual chance, and has a lower annual chance of flooding than the A Zone. Buildings located in this area are not currently required to comply with Appendix G of the Building Code.
In 2015, the City appealed the PFIRMS on the basis that FEMA’s modeling contained technical errors. In October 2016, FEMA agreed to work with the City to revise the 2015 PFIRMs to better reflect current and future flood risk by creating two separate maps: one for flood insurance purposes, and the other for building and planning purposes. However, until the new flood maps are issued, flood insurance rates in New York City will continue to be based on the 2007 effective FIRMs while provisions of the Building Code and Zoning Resolution will continue to be based on the 2007 FIRMs and the 2015 PFIRMs (whichever is more conservative).
In addition to the adoption of the PFIRMs as another standard for how to design buildings in the flood zone, the Building Code was amended to require higher elevations for certain building types: Appendix G incorporates freeboard, an extra margin of protection that requires the lowest floor to be elevated beyond the BFE. This height standard is called the Design Flood Elevation (DFE), which is the BFE plus freeboard (an additional one to two feet of elevation as a measure of safety). Any space below that level needs to be wet-floodproofed or dry-floodproofed (see below) depending on the building use. For example, for buildings located within the A Zones, single- and two-family homes are required to provide two feet of freeboard, and mixed-use or multi-family buildings, are required to provide one foot of freeboard.