Reducing Flood Risk
to Residential
Buildings That
Cannot Be Elevated
FEMA P-1037 / September 2015
The dwelling depicted here and on the cover of this publication sustained flood damage during Hurricane Sandy in 2012. The homeowner
undertook measures to make the dwelling more flood resistant in the future. The structure was retrofitted using some of the techniques featured
in this publication. These techniques include elevating utilities, basement infill, and installation of flood openings. These combined measures will
serve to make the dwelling much more flood resistant and have the added benefit of reducing flood insurance premiums.
Approximate Sandy
ood height
First oor, approximately 2"
above Base Flood Elevation
Subgrade ood vents in
former basement access
Basement inll
with gravel
Elevated utility readable
from standing height
~6.5' above grade
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Reducing Flood Risk to Residential
Buildings That Cannot Be Elevated
Floods can happen anywhere at any time, which is why
it is important to be prepared and to take steps before a
flood event to protect your property from costly damage.
Taking action to reduce the impact of a disaster is known as
mitigation. There are a variety of flood mitigation options
for homeowners—both for newly built homes as well as
existing homes located in floodprone areas. You may be
familiar with mitigation measures such as elevating a home
above the Base Flood Elevation (BFE) or relocating a home
to high ground outside of a high risk flood area. Oftentimes
it is not feasible to elevate residential structures, therefore,
this publication focuses on mitigation measures other than
elevating a home that can be used to protect properties from
flooding, save money over time, and potentially reduce
flood insurance premiums.
Base Flood Elevation: The height to which
oodwater is expected to rise during the base
ood—the ood having a one percent chance of
being equaled or exceeded in any given year. Areas
affected by the base ood are shown as Special
Flood Hazard Areas (SFHAs) on FEMA ood maps.
In 2014, Congress passed the Homeowner Flood Insurance
Affordability Act (HFIAA). In fulfilment of Section 26
of that act, the Federal Emergency Management Agency
(FEMA) has established guidelines for property owners that:
• Provide alternative mitigation methods, other than
building elevation, to reduce flood risk to residential
buildings that cannot be elevated due to their
structural characteristics.
• Inform property owners about how these alternative
mitigation methods may affect flood insurance premium
rates under the National Flood Insurance Program (NFIP).
NFIP flood insurance premiums are based on a number
of factors, including flood risk zone, elevation of the
lowest floor relative to the BFE, the type of building and
foundation, the number of floors, and whether there is a
basement or enclosure below an elevated building. This
publication provides information about measures to reduce
flood risks to residential buildings where elevating the
home is not a viable option.
Lowest oor: The lowest oor of the lowest enclosed
area (including a basement). An unnished or ood-
resistant enclosure, usable solely for parking of
vehicles, building access, or storage in an area other
than a basement area, and having proper openings,
is not considered a building’s lowest oor. Note that
in V Zones if the area under an elevated building
is enclosed, the bottom of the enclosure would be
considered the lowest oor.
Alternative Options for Reducing Your
Flood Risk
Structural elevation is a well-recognized measure for
reducing flood risk and often the most effective measure
to reduce both flood damage and insurance premiums.
Buildings that are situated at or above the level of the BFE
have lower flood risk than buildings below BFE and tend
to have lower insurance premiums than buildings situated
below the BFE. Oftentimes, however, elevation may not be
an option if your home has certain structural characteristics.
These characteristics may include: attached dwelling units;
connected row houses, townhomes, or brownstones; mid-
rise multi-family buildings; older dwellings; and homes
with construction types and/or building materials that are
not suitable for elevation.
This publication describes alternative mitigation measures
intended for a variety of housing types that cannot feasibly
be elevated. The guidance applies to a variety of residential
structures, including single family homes, and many mid-
rise multi-family residential buildings. While the focus is
on 1- to 4-family residential buildings that are one to three
stories tall, the mitigation measures are applicable to other
multi-family and even high-rise residential buildings.
1-4 family home: The NFIP classies insured
buildings into several building types. This publication
addresses 1-4 family homes which include single
family detached homes, row houses, townhomes,
brownstones and mid-rise multi-family buildings.
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Summary
This publication presents a range of ood protection measures available as alternatives to traditional structural
elevation for homeowners whose residences meet both of the following conditions:
1) The residences are existing buildings. This publication is not intended to address construction of new
buildings in oodprone areas as these structures should be sufciently elevated and built in conformance with
NFIP and local oodplain management regulations.
2) The residences are not Substantially Damaged or Substantially Improved, meaning that the buildings have not
sustained damage or undergone improvement (i.e., reconstruction, rehabilitation, addition) where the cost
of the damage or improvement exceeds 50 percent of the market value of the building before the damage
occurred or improvement began. As with new construction, Substantially Damaged or Substantially Improved
structures must be re-built in conformance with NFIP and local oodplain management regulations.
While all of the measures included in this publication can be eff
ective at reducing ood damage, the current
ood insurance rating frame
work does not provide premium reductions for all of the featured measures at the
present time. Even if ood insurance premium reductions are not available, there should still be consideration
given to implementing ood mitigation measures in order to reduce damages and nancial losses.
The following ood protection measures can be rated under the existing NFIP framework such that
implementation of these measures may result in ood insurance premium reductions. The amount of the
premium reduction will vary on a case by case basis.
All Interior Modication/Retrot Measures (Basement Inll, Abandon Lowest Floor, and Elevate Lowest
Interior Floor) and Wet Floodproong using Flood Openings: These measures can moderately to signicantly
reduce ood risk, and the ood insurance rating framework is presently in place to allow homeowners to
receive ood insurance premiums that reect any ood damage reduction protection provided by these
measures. Use of these measures may result in buildings that meet current NFIP minimum requirements
and the local oodplain ordinance, if the lowest oor is elevated to or above the BFE or locally adopted
regulatory ood elevation.
The following ood mitigation measures can be used to decrease ood losses and damages. However, FEMA
will need to undertake further analysis to determine whether it is appropriate to offer ood insurance premium
discounts for undertaking such measures, and if so, what level of discount is appropriate for each measure.
All other Wet Floodproong Measures (Elevate Building Utilities, Floodproof Building Utilities, and use of
Flood Damage-Resistant Materials): These measures can moderately reduce ood risk and damage to
utilities, oors, walls, and other areas subject to ooding.
All Dry Floodproong Measures (Passive Dry Floodproong System) and Barrier Measures (Floodwall with
Gates and Floodwall without Gates, Levee with Gates and Levee without Gates): These measures can
moderately to signicantly reduce ood risk in areas subject to shallow ooding.
A more detailed discussion of each of these alternative mitigation measures and how they reduce ood damages
follows in subsequent sections of this document.
Riverine ooding: Flooding that occurs along a
channel, such as a river, creek, stream, or ditch, when
it receives too much water and the excess ows over
its banks and into surrounding areas.
V Zones: Special Flood Hazard Areas subject to high
velocity wave action.
Coastal A Zones: Inland coastal areas subject to
1.5 to 3 foot waves.
Floodway: The channel of a river and the adjacent
land areas that must be reserved in order to carry
the base ood without increasing ood levels by more
than a designated height, usually 1 foot.
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The measures outlined in this publication are designed
to address slow moving riverine flooding with minimal
debris—the objects floodwaters pick up, such as rocks, dirt,
sewage, ice, and tree branches. Most techniques presented
are not appropriate for high-risk flood hazard areas subject
to wave action (V zones and coastal A zones) or high
velocity flow areas (floodways, areas subject to alluvial fan
flooding, flash flood, mudslide, erosion, or ice jam).
Selection of Mitigation Measures
The ultimate goal of any mitigation measure is to reduce or
eliminate the potential of flood damage in a way that is cost
effective, complies with all applicable floodplain regulations,
and is acceptable to the homeowner in terms of appearance
and livability. The sections that follow include descriptions
of ten flood protection methods. Each description provides
information needed when considering how to protect your
home, including design considerations, costs, effectiveness,
limitations, and potential effect on flood insurance
premiums (additional detail on premium discounts is
provided on page 2 of this publication). Illustrations
that show how the methods are applied are also included.
In some cases, a single method may adequately address
your needs. In other cases, a combination of methods may
be best. Keep in mind, the flood protection method chosen
must meet the floodplain management requirements and/
or building codes of your local community. The methods
included in this publication may not be substituted for
bringing a building into compliance with local floodplain
regulations following a Substantial Damage or Substantial
Improvement determination by local community officials
except where noted.
As you will see in the sections that follow, different
flood protection methods protect your home in different
ways. For example, when you wet floodproof, you allow
floodwaters to enter your home, but prevent damage
below a specified elevation by using flood damage-resistant
materials and construction techniques. When you dry
floodproof your home, you use sealants, shields and other
measures to protect the part of your home below a specified
elevation by preventing water from entering the building.
Because some seepage is anticipated, sump pumps are
used to control the seepage and flood damage-resistant
materials are used to prevent damage where seepage is
likely to occur. When you protect your home with a levee
or floodwall, the top of the levee or floodwall is constructed
to a specified elevation. Other approaches include filling in
a basement or abandoning the bottom floor. For all of these
flood protection methods, the greatest flood damage and
flood insurance premium reductions will be achieved by
floodproofing to/or elevating to or above the BFE.
About the NFIP
In most communities throughout the United
States, construction in oodplains is governed by
combinations of Federal, State, and local regulation.
At the Federal level, FEMA administers the NFIP.
The NFIP is a voluntary program for communities.
Its goal is to reduce the loss of life and the damage
caused by ooding, to help the victims of oods,
and to lower the costs of ood damage borne by the
taxpayer. Communities that participate in the NFIP
take action in several ways:
• Guide future development away from ood
hazard areas.
• Require that new buildings, Substantially
Improved existing buildings, and repair of
Substantially Damaged existing buildings in
the SFHA be constructed in compliance with
oodplain management ordinance, regulation, or
provisions of the building code intended to reduce
ood damage.
Dry oodproong: Sealing your home to prevent
oodwaters from entering.
Wet oodproong: Making portions of your home
resistant to ood damage and allowing water to
enter during ooding.
Flood damage-resistant material: Any building
product (material, component, or system) capable
of withstanding direct and prolonged contact with
oodwaters without sustaining signicant damage.
Examples may include ood damage-resistant
building nish materials such as non-paper-faced
gypsum board and terrazzo tile ooring versus
traditional drywall and carpeted ooring.
Substantial Damage: Damage of any origin
sustained by a building whereby the cost of restoring
the building to its before-damaged condition would
equal or exceed 50 percent of the market value of
the building before the damage occurred.
Substantial Improvement: Any reconstruction,
rehabilitation, addition, or other improvement of a
building, the cost of which equals or exceeds 50
percent of the market value of the building before
the start of construction of the improvement.
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Modifying a home to protect it from flood damage requires
extreme care, will require permits, and may also require
complex, engineered designs. Therefore:
• Engage a “design professional” meaning an architect or an
engineer who is qualified to deal with the specifics of a
flood mitigation project,
• Check your community’s floodplain management
ordinances,
• Check whether government grants are available,
• Hire a qualified contractor,
• Obtain a building permit,
• Determine whether the mitigation project will trigger a
Substantial Improvement declaration,
• See the project through to completion, and
• Obtain an elevation certificate and an engineering
certificate (if necessary).
Interior Modication/Retrot Measures
Interior modification and retrofitting involves making
changes to an existing building to protect it from flood
damage. When the mitigation is properly completed
in accordance with NFIP floodplain management
requirements, interior modification/retrofit measures could
achieve the somewhat similar results as elevating a home
above the BFE.
Keep in mind, in areas where expected base flood depths
are high, the flood protection techniques below alone may
not provide protection to the BFE or, where applicable, the
locall
y required freeboard elevation.
Basement Inll
These measures involve filling a basement located below
the BFE to grade (ground level) (Figure 1). Sections of
the basement walls that remain above ground must be
retrofitted with flood openings that allow automatic entry
and/or exit of floodwaters (refer to the Flood Openings
section for details). Any basement utility systems and
associated equipment must be elevated to protect utilities
from damage or loss of function from flooding (refer to the
Elevate Building Utilities section for details).
Effectiveness: Basement infill has been proven to be
effective at reducing damages to building elements and
contents located below the BFE since the lowest floor can
potentially be re-located above the BFE (see Figure 1).
Considerations: Homeowners must be careful to install and
maintain flood openings that open automatically during a
flood event when needed.
Infill of basements and, if required, relocation of basement
utilities will lead to a loss of square footage and the possible
loss of livable or rentable space within the existing building,
which may not be economically feasible for some owners.
To compensate for the loss of livable or rentable space
within the existing building, additional living space above
the BFE may be added in the form of an added floor or
lateral addition to make up for the loss of the basement.
Unfortunately, adding the cost of the additional living space
may not be economically feasible for some homeowners
and may also trigger a Substantial Improvement declaration.
Figure 1: Basement infill before and after mitigation
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building, which may not be economically feasible for
some homeowners.
To compensate for the loss of livable or rentable space
within the existing building, additional living space above
the BFE may be added in the form of an added floor or
lateral addition to make up for the loss of the lowest floor.
Unfortunately, adding the cost of the additional living space
may not be economically feasible for some homeowners
and may also trigger a Substantial Improvement declaration.
Cost and useful life: Abandoning the lowest floor of a
building is considered a relatively high-cost measure with
an expected useful life of 30 to 50 years and little or no
additional annual maintenance costs beyond maintaining
flood openings.
Potential impact on flood insurance premiums: When the
mitigation is properly completed, a flood insurance policy
will be rated based on the new lowest floor living level. The
higher the reference level of the lowest floor is elevated, the
more significant the premium rate decreases will be. Actual
premium reductions will vary on a case by case basis as
individual structures are rated.
Elevate Lowest Interior Floor
This measure involves elevating the lowest interior floor
within a residential building with high ceilings (Figure 3).
The space below the lowest elevated interior floor walls
must be either filled to create a stem wall or retrofitted
with flood openings that allow automatic entry and/or
exit of floodwaters (refer to the Flood Openings section
for details). Additionally, any utility systems and associated
equipment located below the lowest interior floor must be
elevated to protect utilities from damage or loss of function
Figure 2: Abandoning the lowest floor
Cost and useful life: Basement infill is considered a
relatively high-cost measure with an expected useful
life of 30 to 50 years and little or no additional annual
maintenance costs beyond maintaining flood openings.
Potential impact on flood insurance premiums: When
the mitigation is properly completed, a flood insurance
policy will be rated based on the new lowest floor living
level. The higher the reference level of the lowest floor, the
more significant the premium rate decreases will be. Actual
premium reductions will vary on a case by case basis as
individual structures are rated.
Abandon Lowest Floor
This measure involves abandoning the lowest floor of a two
or more story slab-on-grade residential building (
Figure 2).
The lowest floor walls must be retrofitted with flood
openings that allow automatic entry and exit of floodwaters
(refer to the Flood Openings section for details).
Additionally, any utility systems and associated equipment
on the lowest floor must be elevated to protect utilities
from damage or loss of function from flooding (refer to the
Elevate Building Utilities section for details).
Effectiveness: Abandoning the lowest floor of a building has
been proven to be effective at reducing damages to building
elements and contents located below the BFE (see Figure 2).
Considerations: Homeowners must be careful to install and
maintain openings that open automatically during a flood
event when needed.
Abandoning the lowest floor and, if required, relocation
of utilities will lead to a loss of square footage and the
probable loss of livable or rentable space within the existing
6
from flooding (refer to the Elevate Building Utilities
section for details). To reduce flood damage and flood
insurance premiums to the greatest extent possible, elevate
the lowest floor and utilities to the BFE or above.
Figure 3: Elevating the lowest interior floor before and after mitigation
Effectiveness: Elevating the lowest floor of buildings has
been proven to be effective at reducing damages to building
elements and contents located below the BFE (see Figure 3).
Considerations: Homeowners must be careful to install and
maintain openings that open automatically during a flood
event when needed.
Elevating the lowest interior floor and, if required,
elevating or floodproofing utilities will lead to a loss of
square footage and the possible loss of livable or rentable
space within the existing building, which may not be
economically feasible for some homeowners. Further,
this flood protection measure could trigger a Substantial
Improvement declaration.
Cost and useful life: Elevating the lowest interior floor of
buildings is considered a relatively high-cost measure with
an expected useful life of 30 to 50 years and little or no
additional annual maintenance costs beyond maintaining
flood openings.
Potential impact on flood insurance premiums: When the
mitigation is properly completed, a flood insurance policy
will be rated based on the new lowest floor living level. The
higher the lowest floor is elevated, the more significant the
premium rate decreases will be. Actual premium reductions
will vary on a case by case basis as individual structures
are rated.
Wet Floodproong Measures
Wet floodproofing involves making changes to a home
to allow floodwaters to enter and exit without causing
major damage to the home or its contents (Figure 4). Wet
floodproofing is used in parts of a home that are not used
as living space, such as a crawlspace, basement, garage, or
other enclosure. Allowing water into parts of the home
helps keep the water level inside and outside the home
equal and prevents pressure from the water (known as
hydrostatic pressure) from causing walls to cave in.
Hydrostatic pressure: The pressure exerted
by standing water against walls and concrete
slab oors.
Flood Openings
This measure involves installing openings in foundation and
enclosure walls located below the BFE that allow automatic
entry and exit of floodwaters to prevent collapse from the
pressures of standing water.
Figure 4: Flood openings and their placement
Effectiveness: Flood openings have been proven to be
effective at reducing structural damage to residential
buildings caused by unequal hydrostatic pressures.
Considerations: Homeowners must be careful to install and
maintain openings that open automatically during a flood
event and do not require human assistance.
Cost and useful life: Installing flood openings is considered
a relatively low-cost measure with an expected useful life
ranging from 15 to 20 years with some limited annual
maintenance costs.
Potential impact on flood insurance premiums: Similar to
changing the lowest level in a structure, installation of flood
openings has the potential to increase the elevation at which
the lowest floor is rated and may therefore lower insurance
premiums (see Figure 4). Actual premium reductions
will vary on a case by case basis as individual structures
are rated.
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Elevate Building Utilities
This measure involves elevating all building utility systems
and associated equipment (e.g., furnaces, septic tanks, and
electric and gas meters) to protect utilities from damage or
loss of function from flooding (Figure 5). Homeowners
may elevate building utility systems using a variety of
techniques, including using elevated pedestals or platforms
for outdoor equipment, moving equipment to higher floors
or attic spaces, and building an elevated utility room. To
reduce flood damage to the greatest extent possible, elevate
utilities to the BFE or above.
Freeboard: A factor of safety usually expressed in
feet above a ood level for purposes of oodplain
management. Freeboard accounts for unknown
factors, future development, and oods higher than
the base ood.
Figure 5: Elevate building utilities
Effectiveness: Elevation of all residential building utility
systems has been proven to be effective at reducing or
eliminating utility damage during flood events. Unlike other
alternative mitigation measures, elevating building utilities
is effective against coastal floods or high velocity riverine
flood forces, provided that indoor utilities are elevated to a
higher floor or inside an elevated utility room supported on
piles. Outdoor utilities should be elevated and anchored to a
platform that is attached at one end to the main building.
Considerations: Elevation of residential building utility
systems above expected flood levels may expose the systems
to damage from other types of hazards, such high winds
and earthquakes. However, there are often simple solutions
to address these design concerns.
Cost and useful life: Elevation of all residential building
utility systems is generally considered a relatively moderate-
cost measure with an expected useful life of ranging
from 15 to 20 years with limited annual maintenance
costs. However, the overall cost of the measure can vary
depending on the type of building, the location of utilities,
and the availability of space within the existing building.
Potential impact on flood insurance premiums: Discounts
are currently available under the NFIP for elevating building
utilities in the V Zone. There are also discounts available for
this activity in the A Zone when utilizing the NFIP’s Submit
for Rate Guide.
Floodproof Building Utilities
This measure involves floodproofing all building utility
systems and associated equipment to protect it from damage
or loss of function from flooding (Figure 6). Homeowners
may floodproof building utility systems using a variety of
techniques, including placing outdoor equipment behind
floodwalls or placing indoor equipment behind a wall or
watertight, passive utility enclosure. In order to reduce
flood damage to the greatest extent possible, floodproof to
the BFE or above.
Passive system: Works automatically and does not
require human assistance.
Figure 6: Detail of floodproofed building utility
Effectiveness: Floodproofing residential building utility
systems can be effective at reducing or preventing utility
damage during flood events. This measure is subject to other
restrictions related to flood conditions (3 foot maximum
flood depth, low velocity, short duration) and building
conditions. Floodproofing building utilities will work best
when all utility meters are elevated as well, and flap valves
or passive backflow prevention devices are installed on
building water and sewer lines.
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Flood depth: the height of the oodwater above
the surface of the ground or other feature at a
specic point.
Considerations: Homeowners must be careful to
choose floodproofing systems with openings that close
automatically during a flood event and do not require
human assistance.
Cost and useful life: Floodproofing residential building
utility systems is generally considered a relatively
moderate- to high-cost measure with an expected useful
life ranging from 15 to 20 years with significant annual
maintenance costs needed to maintain various elements
of the floodproofing system. However, the overall cost can
vary depending on the type of building, condition of the
building, and location of the utilities.
Potential impact on flood insurance premiums: N/A
(No premium rate discounts available under the
current program)
Flood Damage-Resistant Materials
This measure involves the use of flood damage-resistant
materials such as non-paper-faced gypsum board and
terrazzo tile flooring for building materials and furnishings
located below the BFE to reduce structural and non-
structural damage and post-flood event cleanup (Figure 7).
Figure 7: Flood damage-resistant materials
Effectiveness: Flood damage-resistant materials have been
proven to be effective at reducing non-structural damage to
residential buildings in low-velocity riverine flood events.
Considerations: Homeowners must be careful to use
materials and assemblies that meet the requirements noted
in FEMA Technical Bulletin 2, Flood Damage-Resistant Materials
Requirements, which is listed in the Resources section.
Cost and useful life: Use of flood damage-resistant
ma
terials is considered a relatively moderate-cost measure
with an expected useful life ranging from 10 to 20 years
and limited annual maintenance costs depending on the
type of material.
Potential impact on flood insurance premiums: N/A
(No premium rate discounts available under the
current program)
Dry Floodproong Measures
Dry Floodproofing involves sealing your home to prevent
floodwaters from entering. Homeowners can dry floodproof
their homes using waterproof coatings or coverings to
prevent floodwater from passing through the walls, install
waterproof shields, and install devices that prevent sewer
and drain backup.
Passive Dry Floodproong System
This measure involves installing a passive (works
automatically without human assistance) dry floodproofing
system around a home to protect the building from flood
damage (Figure 8). The coating or covering must be
impervious to floodwater and certified and constructed to
a maximum of 3 feet above grade (ground level). To reduce
flood damage to the greatest extent possible, floodproof to
the BFE or above.
Figure 8: Dry floodproofed building
Effectiveness: Dry floodproofing of a residential building
can be effective at reducing or eliminating building and
contents damage during flood events. A dry floodproofing
system will work best when all utility meters are elevated as
well, and flap valves or passive backflow prevention devices
are installed on building water and sewer lines.
Considerations: Buildings that are dry floodproofed may be
subject to pressures from standing water and other sources
against the foundation and exterior walls and floor surfaces.
Homeowners may need to make additional changes to their
home, such as reinforcing walls and floor slabs, to resist
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these pressures. This measure also requires the installation of
a drainage system and a back-up emergency power system.
Dry floodproofing of building utilities is subject to other
restrictions related to flood conditions. This measure is most
appropriate where flood depths do not exceed 3 feet, flood
velocities are low, and the duration of flooding is relatively
short. Additionally, the measure is most appropriate for
structures with concrete or masonry walls and a slab-on-
grade foundation.
Cost and useful life: Design and construction of a passive
dry floodproofing system is generally considered a relatively
high-cost measure with an expected useful life ranging
from 15 to 30 years and extensive annual maintenance costs
needed to maintain the various elements of a floodproofing
system. The total cost for dry floodproofing a home will
depend largely on the size of the home, the type and
condition of the wall system, the flood protection elevation,
types of sealant and shield materials used, number of
plumbing lines that have to be protected by check valves,
and number of openings that have to be covered by shields
that need to operate automatically.
Potential impact on flood insurance premiums: N/A
(No premium rate discounts available under the
current program)
Barrier Measures
Barriers, such as floodwalls and levees, can be built around
a home to contain or control floodwaters. A levee is a
manmade structure usually made of compacted soil. A
floodwall is a structure typically made of concrete and/or
masonry and varies anywhere from 1 foot to 6 feet.
Floodwall with Gates and Floodwall without Gates
These two measures involve installing a reinforced concrete
floodwall, which works automatically without human
assistance, constructed to a maximum of 4 feet above grade
(ground level) (Figure 9). The only difference between
the two options is related to openings in the floodwall for
entry and exit. The floodwall with gates is built with passive
flood gates that are designed to open or close automatically
due to the hydrostatic pressure caused by the floodwater.
The floodwall without gates is built using vehicle ramps or
pedestrian stairs to avoid the need for passive flood gates.
Note that sump pumps or an internal storage system along
with a back-up emergency power supply are required
to collect and remove floodwater that collects behind
floodwalls during a flood event. To reduce flood damage to
the greatest extent possible, ensure the top of the floodwall
is at BFE or above.
Figure 9: Residential floodwall
Effectiveness: Construction of floodwalls around a
r
esidential building can be effective at reducing or
eliminating building and contents damage during flood
events. The measures will work best when used along with a
pump system to remove rain that falls within the floodwall
as well as water that seeps through the floodwall.
Considerations: Residential floodwalls are subject to
potential community restrictions and design restrictions
related to flood conditions including low velocity, low
debris, and short duration flood events. They are typically
only cost effective where flood depths do not exceed
approximately 4 feet. Site conditions may also limit the
feasibility of a residential floodwall due to property
limitations for constructing a vehicle ramp or building
entry and exit. Additionally, this measure requires the
installation of a drainage system and a back-up emergency
power system is recommended.
Cost and useful life: Design and construction of floodwalls
is generally considered a relatively high-cost measure with
an expected useful life of 50 years and extensive annual
maintenance costs needed to maintain and inspect the
floodwall. However, the overall cost of the measure can vary
depending on the size of the building, site features, the size
and number of openings, and type of soils surrounding
the building.
Other cost considerations include the need for
professionally designed plans that meet floodplain
management requirements, ensure that the floodwall will
not divert floodwaters or adversely impact neighboring
properties, and that the floodwall and its supporting
drainage system will meet the intended flood protection
design standards.
Potential impact on flood insurance premiums: N/A
(No premium rate discounts available under the
current program)
10
Levee with Gates and Levee without Gates
These two measures involve installing an earthen levee
around a home, which works automatically without human
assistance, with a clay or concrete core constructed to a
maximum of 6 feet above grade (ground level) (
Figure 10).
The only difference between the two options is related
to openings in the levee to enter and exit the property.
The levee with gates is built with passive flood gates
that are designed to open or close automatically due to
hydrostatic pressure caused by the floodwater. The levee
without gates is built using vehicle access ramps to avoid
the need for passive flood gates. Note that sump pumps or
internal storage systems are required to collect and remove
rainwater that collects behind levees during a flood event.
To reduce flood damage and flood insurance premiums to
the greatest extent possible, ensure the top of the levee is at
BFE or above.
Figure 10: Residential levee and typical levee cross section
Effectiveness: Construction of levees around a residential
building can be effective at reducing or eliminating
building and contents damage during flood events. The
measures will work best when used along with a pump
system or interior storage system to address rain that falls
within the levee.
Considerations: Residential levees are subject to design
restrictions related to flood conditions including low
velocity, low debris, and short duration flood events. They
are also only cost feasible to approximately 6 feet maximum
flood depth. Site conditions may also limit the feasibility
of a residential floodwall due to property or building entry
and exit. Additionally, this measure requires the installation
of a drainage system and a back-up emergency power
system is recommended.
Cost and useful life: Design and construction of levees is
generally considered a relatively high-cost measure with an
expected useful life of ranging from 50 to 100 years and
significant annual maintenance costs needed to maintain
and inspect the levee. However, the overall cost of the
measure can vary depending on the size of the property to
accommodate the levee and any vehicle ramps, site features,
availability of suitable materials, size and number of
openings, and type of soils surrounding the building.
Other cost considerations include the need for
professionally designed plans that meet floodplain
management requirements, ensure that the levee will
not divert floodwaters or adversely impact neighboring
properties, and that the levee and its supporting
drainage system will meet the intended flood protection
design standards.
Potential impact on flood insurance premiums: N/A
(No premium rate discounts available under the
current program)
Comparison of Alternative Mitigation Measures
The alternative mitigation measures presented here are
suitable for use in reducing or eliminating the potential
of future flood damage to existing residential buildings.
Suitability was evaluated based on a number of factors,
including:
• Passive Measures: The mitigation measure must be passive,
meaning that it works automatically and does not require
human assistance. Passive measures, which do not require
human assistance, tend to be more effective than active
measures, which require human intervention.
• Level of Protection: The degree to which the measure allows
protection to or above the BFE. Measures that provide
protection to or above the BFE are preferable to those that
provide less protection.
• Flood Hazard Conditions: The extent to which the measure
is effective as floodwater velocities increase. Only flood
protection methods suitable for low velocity, low debris,
and short duration flooding conditions were considered.
• Effectiveness as a Stand-Alone Measure: The effectiveness of the
measure on its own at reducing flood damages without
the need for any additional measures or techniques.
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Table 1
Mitigation Measure Life Cycle Cost
Expected
Useful Life
Design
Complexity
Potential for Reducing
Flood Damage
Wet Floodproofing Measures
Flood Openings Low 15–20 years Low High
Elevate building utilities Low to Moderate 15–20 years Low Moderate
Floodproof building utilities Low to Moderate 15–20 years Moderate Limited
Flood damage-resistant materials Moderate 10–20 years Moderate Limited
Dry Floodproofing Measures
Dry floodproofing system High 15–30 years High Moderate
Barrier Measures
Floodwall with or without gates High 50 years High Moderate
Levee with and without gates High 50–100 years High Moderate
Interior Modification/Retrofit Measures
Basement infill Moderate to High 30–50 years High High
Abandon lowest floor Moderate to High 30–50 years High High
Elevate lowest interior floor Moderate to High 30–50 years High High
• Life Cycle Cost: Initial cost plus annual costs needed to
install, operate, and maintain the effectiveness of the
measure over the expected project useful life.
• Design Level of Effectiveness: The extent to which the measure
provides protection (e.g., protection to or above BFE) and
the expected damages once that level is reached.
• NFIP Compliance: The extent to which the measure either
meets or fails to meet NFIP requirements for new
and Substantially Damaged/Substantially Improved
residential buildings. Structures that are Substantially
Damaged following a hazard event must be brought into
compliance with NFIP regulations. Similarly, any measure
that triggers the Substantial Improvement threshold will
require that the structure is brought into compliance with
the NFIP regulations.
• Role of Design Professionals and Building Officials in the Permitting
Process: Many alternative mitigation measures presented
here will require design and construction oversight by
a licensed design professional (Registered Architect/
Professional Engineer). In addition they will likely need
review, approval, and permits from the local jurisdiction.
• Potential for Reducing Insurance Premiums: The likelihood
of the measure to produce measurable annualized
project benefits that justify a reduction in NFIP flood
insurance premiums.
Table 1 compares the mitigation methods and summarizes
the life cycle cost, expected useful life, design complexity,
and potential risk reduction for each of the mitigation
measures. If your home is being Substantially Improved
or has been Substantially Damaged, the NFIP regulations
limit your choice of methods to those shown in the Interior
Modification/Retrofit Measures section of the table. If
your home is not being Substantially Improved or has not
been Substantially Damaged, any of the methods presented
may be considered as long as the cost of the mitigation
project does not result in your home being considered
Substantially Improved.
Case Studies
The final consideration in choosing a mitigation technique
is deciding if its benefits outweigh its costs. Two case
studies are provided here to show the flood insurance
rate reductions and the time needed to recover the cost
of the mitigation project based on the flood insurance
discount. Individual results will vary based on building
characteristics, site conditions, and BFE in relation to the
lowest floor of the building.
Case Study 1 - Flood Openings
This measure involves installing openings in foundation and
enclosure walls located below the BFE that allow automatic
entry and exit of floodwaters. Installing flood openings is
considered a relatively low-cost measure. Refer to Figure 4
for an example of this technique.
12
The example below shows the flood insurance premium
before and after the flood mitigation project on a single
family one-story home without a basement on a crawlspace
foundation located in an AE Zone where the first floor
elevation above the crawlspace is 4 feet above the BFE.
Estimated cost range: $6,300 to $9,500 including
annual maintenance
Useful life: 15 to 20 years with limited annual
maintenance costs
Current annual flood premium: $1,147 for maximum
coverage ($250,000 building and $100,000 contents)
Estimated annual flood insurance premium
post mitigation: $610 for maximum coverage
Estimated annual reduction in premium: $537
Estimated time to recover mitigation cost: 12 to 18 years
AE Zone: Areas within FEMA’s mapped 1% annual
chance oodplain where base ood elevations
are provided.
Case Study 2 - Basement Inll
This measure involves filling a basement located below the
BFE to grade (ground level) Basement infill is considered
a high-cost measure. Refer to Figure 1 for an example of
this technique.
The example below shows the flood insurance premium
before and after the flood mitigation project on a concrete/
masonry wall single family two-story home with a
basement located in an AE Zone where the first floor
elevation above the basement is at the BFE. To compensate
for the loss of square footage and living space, a second
story has been added.
Estimated cost range: $72,000 to $108,000 including
annual maintenance
Useful life: 30 to 50 years and little or no additional annual
maintenance costs beyond maintaining flood openings
Current annual flood premium: $6,537 for maximum
coverage ($250,000 building and $100,000 contents)
Estimated annual flood insurance premium
post mitigation: $1,631 for maximum coverage
Estimated annual reduction in premium: $4,906
Estimated time to recover mitigation cost: 15 to 22 years
Financial Assistance
FEMA and other Federal agencies have an array of grant
programs to assist States, communities, and individual
property owners in mitigating the negative effects of
flooding. You may be eligible to receive financial assistance
through one or more of these programs that will help pay
for some of the mitigation measures presented here. More
information can be found on the FEMA Hazard Mitigation
Assistance Web site at http://www.fema.gov/hazard-
mitigation-assistance or by contacting the FEMA Regional
Office for your State, your NFIP State Coordinator, or your
State Hazard Mitigation Officer.
Summary
Before applying any of the alternative mitigation measures
described in this publication,
• contact your local building department to learn about
development and permit requirements in your area;
• consult a registered design professional (architect or
engineer) to determine which options may be best for
your home;
• contact your insurance agent to find out how your flood
insurance premium may be affected;
• learn about what financial assistance might be available to
help pay for the measures.
Resources
The FEMA resources in this section offer more information
about the alternative mitigation measures in this
publication. For technical assistance on any of these FEMA
resources, you may contact FEMA’s Building Science
Helpline, a technical assistance hotline, at 1-866-927-2104
(phone) or [email protected]v (email).
Above the Flood: Elevating Your Floodprone House
(FEMA P-347)
http://www.fema.gov/media-library/assets/
documents/725
Engineering Principles and Practices for Retrofitting Flood-
Prone Residential Buildings (FEMA P-259)
http://www.fema.gov/media-library/assets/
documents/3001
Flood Damage-Resistant Materials Requirements
(Technical Bulletin 2)
http://www.fema.gov/media-library/assets/
documents/2655
Homeowner’s Guide to Retrofitting (FEMA P-312)
http://www.fema.gov/media-library/assets/
documents/480
Hurricane Sandy Recovery Advisory: Reducing Flood
Risk Flood Insurance Premiums for Existing Residential
Buildings in Zone A (RA7)
http://www.fema.gov/media-library-data/
1385402350525-0854e30dc59e2567554b87bc3cc94e36/
SandyRA7ReducingFloodRisk_111913-508.pdf
Openings in Foundation Walls and Walls of Enclosures
(Technical Bulletin 1)
http://www.fema.gov/media-library/assets/
documents/2644
Protecting Building Utilities from Flood Damage
(FEMA P-348)
http://www.fema.gov/media-library/assets/
documents/3729
Wet Floodproofing Requirements (Technical Bulletin 7)
http://www.fema.gov/media-library/assets/
documents/3503
FEMA P-1037
Catalog No. 15252-1
