FEDERAL EMERGENCY MANAGEMENT AGENCY
90
CHAPTER 5
flooding and other hazards at the site. If changes must be made to the
foundation to increase its strength and stability, they can be made as part
of your retrofitting project, but they can increase both the cost of the
project and the time required to complete it.
The type of foundation on which your house was originally built
(basement, crawlspace, slab-on-grade, piers, posts, pilings) also can
affect the elevation process. This issue is discussed later in this chapter,
in the section
The Elevation Techniques.
Hazards
Because so many elevation techniques are available, elevation is practical for
almost any flood situation, but the flooding conditions and other hazards at
the house site must be examined so that the most suitable technique can be
determined. Regardless of the elevation technique used, the foundation of
the elevated house must be able to withstand, at a minimum, the expected
loads from hydrostatic pressure, hydrodynamic pressure, and debris impact.
It must also be able to resist undermining by any expected erosion and scour.
If you are elevating a house in an area subject to high winds, earthquakes, or
other hazards, a design professional should determine whether the elevated
house, including its foundation, will be able to withstand all of the horizontal
and vertical forces expected to act on it. In making this determination, the
design professional must consider a number of factors, including the structure
and condition of the house, the soil conditions at the site, the proposed
elevation technique, and the hazards at the site. The conclusion may be that
additional modifications must be made during the retrofitting project.
Access
Elevating a house usually requires that new means of access be provided.
For example, if your entry doors were originally at ground level, new
staircases, elevators, or ramps will have to be built. When an attached
garage is elevated, providing access for vehicles may require changes to
portions of your lot, such as building a new, elevated driveway on earth fill
that ties into high ground elsewhere. This solution can be practical when the
amount of elevation required is no more than 2 or 3 feet. As noted earlier,
when the amount of elevation reaches 4 or more feet, you should consider
elevating your house a full story so that you can use the lower level for
parking and avoid the need for an elevated driveway.
The need to provide new means of access is often the main objection that
homeowners have to elevating. But functional and attractive solutions to
this problem can usually be developed, as shown in Figure 2-2 in Chapter 2
and Figure 5-3.
WARNING
Placing fill in floodways
and Coastal High Haz-
ard Areas is normally
prohibited. Check with
your local officials about
State and local require-
ments concerning the
use of fill.