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Floodproofing, FEMA and flood maps
November 13, 2019
The following is an interview between Randy Lewis, VP of Loss Prevention Education, Design Professional and Adam Reeder, PE, CFM, Senior Project Manager and a principal at CDM Smith, a full-service architectural and engineering firm headquartered in Boston, Massachusetts. Since 2007, Reeder has been working with the U.S. Federal Emergency Management Agency (FEMA) on dry floodproofing and other disaster issues. He also recently completed the flood-related portion of an economic analysis report for the National Institute of Building Sciences entitled Mitigation Saves 2.0.
Randy asked Reeder to help enlighten designers about the dangers of overreliance on FEMA flood maps when working in areas with flooding potential and the risks associated with signing FEMA floodproofing certificates. He spoke to us from his office in Raleigh, North Carolina.
Randy Lewis: You’ve expressed serious concern about the tendency of design professionals to rely too heavily on FEMA’s flood insurance rate maps, or FIRMs, when determining the elevation of a structure’s foundation. What’s wrong with these FIRMs?
Adam Reeder: There’s nothing wrong with them as long as they’re used for their intended purpose, which is insurance rating, and not used as the sole source for design information. FIRMs indicate the Base Flood Elevation (BFE) and are the maps referenced by local ordinances, building codes, and design standards as the basis for calculating the minimum required elevation. Think of them as a starting point for designers.
RL: What’s their insurance-related purpose?
AR: FEMA initially created the maps so the National Flood Insurance Program (NFIP) could rate buildings within a floodplain. The maps are used to compare a reference elevation, such as the elevation of the top of the lowest finished floor, to the elevations (BFEs) presented on the maps, which are based on the one-percent annual chance of a flood, also referred to as the chance of a 100-year flood.
RL: Why have the FIRMs been adopted for use by designers?
AR: More than 20,000 communities participate in the NFIP. Since participation requires a community to adopt the FIRMs in its floodplain ordinances, local building codes eventually adopted the maps as the minimum standard that builders must meet. The FIRMs are the most widely available source for flooding information.
RL: Why shouldn’t designers rely so much on the FIRMs?
AR: The maps represent the probable flood patterns at the time FEMA did the hydraulic and hydrology modeling. If a map has been updated, a designer must determine whether the map reflects new modeling or whether there was some other change that FEMA recognized (e.g., incorrect elevations on the map that may not change the flooding dynamics) and revised the map without re-running the flood modeling. A map with a 2009 date could represent modeling done in the 1980s. Overall, the maps represent the best available data at the time the modeling was done. A lot can change in a community in 20 or 30 years—roads are paved, new developments arise, forests are cleared and so on. All of these factors could increase flood heights. We should also remember that the maps are intended to represent current conditions— designers should think about changing flood conditions over the life of a building and design with these changes in mind.
RL: When an area is hit with major flooding, does FEMA take any immediate action to upgrade the maps?
AR: Whenever there’s major flooding, such as in Houston with Hurricane Harvey, FEMA will study the affected area. They’ll create advisory maps that are conservative and probably set elevations higher than reality just to be safe. They’ll tell communities to use those until the agency can do more detailed maps, which usually takes about three years. The communities then need to formally adopt the maps in order for them to be considered effective.
RL: Do the maps account for future climate change?
AR: No. Since these are produced for insurance purposes, they represent the now. But, obviously, climate change is something designers want to take into account, because what they design is most likely intended to last for 30 years or longer.
RL: How can A/Es be confident they’re using the latest information available?
AR: The first step is to go to the FEMA website, where you can look at historical map products. I tell people to compare the flood elevations over a series of maps to determine whether there have been any changes to the modeling. Did FEMA re-run the modeling or did they change the map for some other reason? Designers can also check with local community officials to find out if there’s any additional flood modeling information available. Designers should also keep in mind that the elevation printed on these maps represents the median elevation for the 100-year or one-percent-annual-chance storm. You could have 100-year events higher and lower than that median elevation.
You should be looking at additional sources. For example, if you’re on a river, look at some river gauge data. If you find some instances of the 100-yearflood elevation being exceeded, that suggests that you should build to a higher elevation, because there is a possibility that flooding at or above the mapped 100-year flood elevation is more frequent at the building site. The building or the housing development you’re designing doesn’t even need to be in the floodplain for you to be concerned. It could just be in an area that’s draining into the floodplain and now more of the rainwater is running downhill and into the stream or river and filling it up more frequently than you thought it would.
RL: Given that these maps may or may not be reliable, what do you consider to be the designer’s responsibility when designing a new structure?
AR: Unfortunately, I think many designers regard the engineering standard’s minimum required elevation as the required elevation. The designer should be telling the owner, “I’ve looked at these other factors and I think the minimum required elevation is too low, because there’s additional risk not accounted for.” Now, if the owner chooses to ignore your advice and you can document that, then I think you can feel like you’ve done what you could. FEMA often sends us out after a disaster to look at building performance. I’ve never heard a building owner say, “I could have gotten away with doing less and I would have been fine.” What I often hear is, “Thank goodness I built higher.” The bottom line is, the FIRMs are not an ending point but a starting point.
RL: There’s another aspect to designing buildings within NFIP-member communities, and that’s FEMA’s “Floodproofing Certificate for Non-Residential Structures.” How is that used?
AR: In some cases, mainly non-residential construction, buildings in the regulated floodplain can be built below the required elevation, as long as the building is designed to keep the water out and the walls and slab of the building are certified as being “substantially impermeable” and meeting specific engineering requirements referenced in the certificate. That certificate was developed primarily because the NFIP requires certification that a building has been floodproofed up to a specific elevation, which is usually the BFE plus one foot. When a designer signs the certificate, they’re certifying not only that they’ve designed to that requirement, but also that the contractor has constructed the building to that requirement.
RL: Why would a designer ever sign such a certification?
AR: Often, it’s because they’re not asked to sign it until the end of the project. They may feel their backs are against the wall, particularly if they haven’t been paid in full. If they don’t know ahead of time about the certificate, they most likely haven’t priced their services to include special inspections to verify the work was properly performed.
RL: What if the designer performed construction contract administration services throughout the project?
AR: Then they might feel confident certifying the building initially, but FEMA requires that the building be re-certified when the NFIP insurance policy is renewed. The problem is that there may have been changes to the building that rendered it less than floodproofed. For example, we’ve seen owners install pipes through exterior walls that are below the flood protection level, resulting in a penetration that hasn’t been properly sealed. It doesn’t take a great deal to nullify the floodproofing. Many owners may think it’s a matter of a designer just signing the certificate and may balk at the cost to inspect the building in order to re-certify. The certification also states that the building meets the requirements of a consensus flood-resistant design and construction standard called ASCE 24-14. It states, among other things, that the designer has met several requirements regarding operations and maintenance plans and made sure that the system they designed can be implemented.
RL: And yet, designers still sign these certificates?
AR: Yes. When a client asks them to sign it, I think they either quickly scan it or, if they do read it, they don’t realize what is required to correctly dry floodproof a building or the full implications of signing the certificate. If the building does flood without overtopping the elevation covered by the certificate, it won’t take a very savvy lawyer to look at the ASCE 24-14 and figure out that, potentially, some of the responsibility for the building flooding falls on the architect or the engineer.
RL: What should designers do when they’re presented with the certificate and a pen at the end of a project?
AR: In most instances, I would not feel comfortable signing it. But I probably wouldn’t pursue any projects that are going to require me to sign the certificate. And if I did, I would budget enough inspections, during and after construction. I’d also tell the owner that if I have to re-certify at the time of insurance renewal, I will include in my price the expense of doing an evaluation and working with product manufacturers to do field testing to determine whether their products are maintaining their effectiveness. I’d also require the owner to certify in writing that there have been no modifications below the flood protection elevation, either during construction or since the last insurance renewal. Owners need to share the responsibility for floodproofing.
RL: Given that many designers will continue to accept projects in floodprone areas, what are the main loss prevention points you’d like to leave with our readers?
AR: (1) Take time to educate yourself on flood risk and mitigation. FEMA’s Building Science Branch has several publications on flood design and post-disaster assessments that could influence design decisions.
(2) Remember that the engineering standards and codes represent the minimum flood requirements. A little effort will make you more aware of the flood risk at a building site. Also, check to see if there are any local requirements that might exceed those mentioned in the building codes.
(3) Document your design decisions and inform your client that, in addition to reducing risk, going higher than required can result in potential flood insurance premium discounts. We know that going above the minimum requirements also reduces flood losses. Think of it as a responsibility you share with the owner.
(4) Flood design isn’t just about elevation. The velocity, debris-impact risk, rate of rise for the water, duration of flooding, and wave heights are additional factors that might influence your design decisions.
(5) If you’re considering designing a dry floodproofing project, make sure you understand the building code, engineering, and insurance requirements before agreeing to the project.
Adam Reeder may be contacted at firstname.lastname@example.org or 919 325 3526.