FEMA Flood Map Changes
As part of the National Flood Insurance Program, FEMA has undertaken the effort to map flood risk areas across the nation. These maps are called Flood Insurance Rate Maps (FIRMs). Each community that participates in the National Flood Insurance Program has a set of FIRMs that cover the community. The purpose of these maps is to delineate flood risk areas, which are normally shown as shaded areas on the map, and often designate how high (above sea level or “datum”) FEMA expects flood waters to stretch, which is called the base flood elevation, or BFE. Over the last decade, these maps have evolved, and the changes can have an impact on insurance costs.
Early Flood Maps
Early flood maps were very crude, lacked detail, and were often not based on sound topographical data and flood risk analysis. For Pasco County, the first set of FIRMs shaded flood risk areas, but did not specify any base flood elevation information. Below is an example from the Feather Sound area of Pinellas County. Note that the flood zone lines are drawn straight, and only major highways are shown for reference points. In this area, the maps also underestimated the flood risk, and modern maps raised the base flood elevation by 2 or more feet.
1980s and 1990s Revisions
1980s and 1990s era maps had better detail, more roads and other features to use as points of reference, and were often based on better topographic data and flood risk analysis. In addition, more base flood data were included. Below is an example of a 1990s era map from Pasco County.
Modern Flood Maps
Below are samples of modern and very detailed FIRMs from
Hernando County. Newer maps often
have more detail which include colors and are overlaid onto an aerial photograph
or parcel map. Some of the maps
utilize newer technology, such as LIDAR, to provide a more accurate topographic
base map. In some cases, the newer
maps designate the base flood elevation to the nearest tenth of a foot.
It should also be noted that another important change is being made with
the newly issued maps. FEMA is
converting from the use of the NGVD 1929 elevation datum to the NAVD 1988
elevation datum. In the Tampa Bay
area, the difference is approximately -0.90 feet.
Therefore, when you compare the new maps to the old maps, you will often
see that flood elevations have been lowered by 1 foot in certain areas.
This does not mean that the flood risk has been reduced by 1 foot, it is
simply an adjustment to reflect the datum change.
Another significant change in the newly issued maps is that they are county
wide, including both incorporated cities and unincorporated county areas on the
same maps, which makes these maps easier to work with.
Viewing Current, Historic, and Future Flood Maps
FEMA has made both the current and historic Flood Insurance
Rate Maps (FIRMs) available at their website, http://www.msc.fema.gov.
In addition, if your community is in the process of updating and
approving a new set of FIRMs, you may be able view preliminary maps at the above
Once at the above referenced website, click “Product
From there, you will see that the top three links are to
Effective, Future, and Historic FIRMs.
Select the era of maps you wish to view, and then you will
be prompted for your State, County, and Community.
If you do not live within an incorporated city limits, you will most
likely select your county’s name for community.
Then select the button to get the maps.
If you happen to know your map number, it should be easy to find. If not, it is best to view the map index, which normally includes the letters IND under the “Item ID” column. Please note that when viewing Historic Maps, there may be multiple versions of the same area, and multiple index maps. If you are interested in maps from a certain date, you can sort the maps by “effective date”, then locate the maps and index that were effective at that time.
One of the most extreme examples of flood map changes that
I’ve come across occurred in the Flor-A-Mar area of Pasco County.
This involved homes built in the 1970s.
The first flood map (1977) for this area designated the area to be Zone A
with no base flood elevation determined. This
often meant that the building heights were left to the county building
department to determine. Many homes
were built in accordance with these county requirements.
In 1981, the flood maps were revised, and the flood zone
was changed to A11 with a base flood elevation of 12’.
Many homes were built in accordance with the new base flood elevation.
In 1984, the map was again revised, and this time, the zone was changed to V17, with a base flood elevation of 16’.
This is a very significant change, not only in that the base flood elevation was again changed, but also that the Zone designation was changed from “A” to “V”. “V” is considered to be the most hazardous zone, and in addition to the requirement of higher building elevation, zone “V” also requires much more strict building designs, such as “break away walls” and “building elevated on piling or columns”. Needless to say, homes constructed in this area to the minimum building requirements between 1977 and 1984 are now considered woefully out of compliance with the newest flood maps and building codes, which can affect flood insurance rates. There are many more cases like this in all across Florida.
One of the basic tenants of the modern day building code is
that when a home is constructed within a flood zone, the elevation of the
home’s living floor must be at or above the effective base flood elevation as
specified by the FIRM.
Map changes can often have a detrimental effect on how a
home is rated for flood insurance purposes.
As you can imagine, it is often the case that when maps are updated,
flood zone lines changed, and base flood elevations raised or lowered, homes that
were built in compliance with a previous map are often now out of compliance
with the current set of FIRMs. Sometimes
homes that were initially built outside of the flood zone lines are shown to be
within the flood zone lines on newer maps. Also,
it is often the case that when new maps are issued, the base flood elevation is
effectively raised for some areas. Therefore,
any house previously built in that area to the minimum elevation would be shown
to be too low based on the new maps.
FEMA policy used to have a “grandfather clause” which protected home owners from rate increases due to map changes. However, recent changes in federal law have altered this policy, and now map changes may result in steep increases in flood insurance rates. You can read more about the law changes here.