The most costly and frequent natural disaster in the United States is flooding, and the last several years of U.S. disaster data tell the story: In 2017, 80 percent of FEMA’s disaster spending was on flood-related events. And a recent study by the National Association of Insurance Commissioners shows that 90 percent of natural disasters in the U.S. involve flooding.
That’s why, of the four main functions of the National Flood Insurance Program (NFIP), one of the most important is floodplain-management standards, which are the construction standards for building in a high-risk flood zone. When a building is constructed in any mapped high-risk flood zone in a participating community, it must meet floodplain-management standards to eliminate the inherent flood risk. FEMA estimates that this saves the U.S. $1.7 billion a year in flood losses.
Since the enactment of the National Flood Insurance Act in 1968, our understanding of risk has evolved, but the NFIP minimum floodplain-management standards have not. The Code of Federal Regulation that outlines the NFIP’s standards remains mostly unchanged since its start. However, the International Building Code (I Codes) and local municipality bylaws have built in more resilient standards over time.
In 2008, FEMA issued guidance and mapping for a new floodplain-management guideline known as the Limit of Moderate Wave Action (LiMWA). The LiMWA created a new flood zone called the coastal “A” zone, and its implications for construction can be significant. Because the LiMWA is not found within the NFIP’s regulations, there can be a disconnect between the LiMWA, implementation, and enforcement; as well as the rating for flood insurance and what it really means for construction requirements.
The LiMWA, by definition, is “the inland limit of the area expected to receive 1.5-foot or greater breaking waves during the one-percent-annual-chance flood event.” But why do the LiMWA and coastal “A” zone exist, and how do they differ from any other flood zone?
Flood Map Basics
Under modern flood maps, there are primarily three types of flood zones: the V zone, A zone, and X zone. When the V and A zones have flood elevations known as Base Flood Elevations (often represented as BFE) associated with them, they are known as VE and AE zones. V zones and A zones are called Special Flood Hazard Areas (SFHA); these zones both have a one percent chance of flooding annually, and mandatory flood insurance is required if there is a federally backed mortgage.
In an SFHA, the NFIP requires, at a minimum, the lowest occupiable floor of a building to be at least as high as the Base Flood Elevation stated in that particular zone. States and local municipalities can enforce stricter floodplain-management standards than the NFIP minimums, and those local standards, which typically rely on the I Codes, will supersede NFIP minimums.
The most recent edition of the I Codes requires a structure to be built or dry floodproofed one foot higher than the Base Flood Elevation in any SFHA (some state and local codes go even further). Additionally, the I Codes rely on ASCE-24, an engineering standard for flood-resistant construction.
Where Coastal A Zones and LiMWA Come In
In a V zone, Base Flood Elevations include wave heights equal to or greater than three feet. In A zones, Base Flood Elevations include wave heights less than 1.5 feet. But, as FEMA began to study field data and do lab tests on actual damage after large events, it found that there is a middle area in coastal communities that sees damage between the V zone and A zone wave heights. FEMA deemed this area the “coastal A zone,” which is depicted in figure 1.
The LiMWA, as defined earlier, is a line representing the inland limit of the coastal A zone (see figure 1), and the coastal A zone’s seaward extent is the adjacent V zone boundary.
All recent FEMA flood maps in coastal counties now include a LiMWA line. However, identifying the coastal A zone can still be complicated. The coastal A zone, as defined by the LiMWA, is only labeled as an A zone on flood maps, with no special wording or labeling to indicate it as “coastal.” The only delineator between the non-coastal A zone and the coastal A zone is the LiMWA line. Complicating matters further, the LiMWA line only started to be printed on maps in the last 10 years.
Where It Gets Tricky for Builders
For construction and floodplain management, enforcement of the LiMWA can vary greatly. For example, in Massachusetts, the state has adopted the I Codes, which should automatically enforce the LiMWA. However, the state has a specific amendment exempting LiMWA enforcement. Still, if a project, such as a home elevation, uses federal dollars, such as in a Hazard Mitigation Grant, then the LiMWA must still be enforced, even if the state does not enforce it.
This confusion can leave projects in a bind at the last minute. Since the LiMWA is not identified in the NFIP minimum standards, it is critical that, when building in a coastal area, contractors and builders are clear about whether the project is in a coastal A zone, and if the jurisdiction enforces the requirements of coastal A zones.
If building in a coastal A zone, the standards for construction—as identified in the I Codes and ASCE-24—state that you must follow most of the construction standards of a V zone, rather than a non-coastal A zone. This means, in a coastal A zone, the building must be built on piers, post, and piles; the lowest floor must be built at least one foot above the Base Flood Elevation; and the area below the lowest floor must have break-away walls, among other requirements (refer to I Codes and ASCE-24).
Typically, the LiMWA poses a challenge to contractors, builders, and designers who may fully design a project to non-coastal A zone standards without knowing they could be in a coastal A zone. In addition, complying with coastal A zone standards, when they are enforced, can increase costs and completely change the project’s scope.
For example, in a non-coastal A zone, a commercial building can be dry floodproofed. Dry floodproofing allows the lowest floor to be built below the Base Flood Elevation as long as some strict building standards are met. A commercial building in a coastal A zone, however, cannot be dry floodproofed.
V Zone for Standards; A Zone for Insurance
So if the floodplain-management standards of the coastal A zone are treated almost exactly the same as a V zone, is there a difference between the two flood zones? The answer is yes, and the biggest difference is in the rating of flood insurance. While the coastal A zone may have different building and construction standards from a non-coastal A zone, the NFIP rates a structure in a non-coastal A zone the same as a coastal A zone.
However, because of the the higher floodplain-management standards in a coastal A zone, there are benefits with respect to flood-insurance affordability and the resilience of the structures. For example, to meet the minimum I Code standard in the non-coastal A zone, the lowest finished floor must be at least one foot above the Base Flood Elevation.
The rate for a residential home built to this standard is $721 (based on $250,000 of insurance, $10,000 deductible, and a one-story building with no enclosure). However, in a coastal A zone, as defined by the LiMWA, the bottom of the lowest horizontal member must be one foot above the Base Flood Elevation.
Since FEMA rates non-coastal and coastal A zones identically, the point for rating remains at the top of the finished floor. Therefore, the finished floor would be elevated at least another foot in the coastal A zone, making the rate $458.
Older Structures and
Extra Incentives
The rates mentioned above are for new construction. The LiMWA will have the biggest impact on older structures, where rates can be as high as $15,000 to $20,000 a year through the NFIP. If a large storm strikes and a community must rebuild substantially damaged structures, those structures will now have to comply with the current flood maps and codes enforced in that community. If a building that was previously paying $15,000 in flood insurance is rebuilt to current standards, the flood-insurance savings are not only significant for the building owner, but also the new standards add to the community’s resiliency.
The incentive for the enforcement of the LiMWA extends beyond resilience and insurance rates. The Community Rating System (CRS) offers credit points for LiMWA enforcement. CRS, a program found within the NFIP, gives discounts on flood insurance to communities that perform and document various activities found in the CRS manual aimed at making communities more resilient.
The CRS manual notes, “Wave-tank studies have shown that breaking waves lower than the three-foot criterion used to designate VE Zones can cause considerable damage,” and it awards up to 500 points for the LiMWA-enforcement activity.
Whether or not a community or state enforces the LiMWA, FEMA encourages higher and safer building. In published bulletins, it states, “Residents and business owners living or working in the coastal A zone should be aware of the potential wave action and the accompanying damage that could occur. Property owners are encouraged to build safer and higher to minimize the risk to life and property…. The LiMWA is provided to communicate the higher risk that exists in the area. Because the 1.5-foot breaking wave in the LiMWA zone can potentially cause foundation failure, communities are encouraged to adopt building-construction standards similar to zone VE in those areas.”
The LiMWA that defines the coastal A zone is an effort to further avoid losses and make our coastal communities more flood resilient. Over time, the hope is that coastal A zones are enforced in all coastal communities. The goal is to not only affect the affordability of insurance for these structures, but also minimize their future losses in flooding events.