elevating your house
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H O M E O W N E R S G U I D E T O R E T R O F I T T I N G 87
Elevating Your House
IntroductionOne of the most common retrofitting methods is elevating a house to arequired or desired Flood Protection Elevation (FPE). When a house isproperly elevated, the living area will be above all but the most severefloods (such as the 500-year flood). Several elevation techniques areavailable. In general, they involve (1) lifting the house and building a new,or extending the existing, foundation below it or (2) leaving the house inplace and either building an elevated floor within the house or adding anew upper story.
During the elevation process, most frame, masonry veneer, and masonryhouses are separated from their foundations, raised on hydraulic jacks, andheld by temporary supports while a new or extended foundation isconstructed below. The living area is raised and only the foundation remainsexposed to flooding. This technique works well for houses originally built onbasement, crawlspace, and open foundations. When houses are liftedwith this technique, the new or extended foundation can consist of eithercontinuous walls or separate piers, posts, columns, or pilings. Masonryhouses are more difficult to lift, primarily because of their design, construction,and weight, but lifting these homes is possible. In fact, numerous contractorsthroughout the United States regularly perform this work.
A variation of this technique is used for frame, masonry veneer, andmasonry houses on slab-on-grade foundations. In these houses, the slabforms both the floor of the house and either all or a major part of thefoundation. Elevating these houses is easier if the house is left attached tothe slab and both are lifted together. After the house and slab are lifted, anew foundation is constructed below the slab.
For masonry houses on slab-on-grade foundations, some homeownersfind it easier to use one of two alternative elevation techniques, in whichthe house is left on its original foundation. One technique is to remove theroof, extend the walls of the house upward, replace the roof, and thenbuild a new elevated living area inside. The second is to abandon the
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existing lower enclosed area (the level with the slab floor) and move theliving space to an existing or newly constructed upper floor. Theabandoned lower enclosed area is then used only for parking, storage,and access to the house.
In both of these techniques, portions of the original walls will be below theFPE. This approach is appropriate for masonry construction, which isnaturally flood-resistant, but not for frame construction, which could easilybe damaged by flood waters.
This chapter describes and illustrates the various elevation methods anddiscusses the most important considerations regarding elevation.
ConsiderationsAmount of Elevation
The amount of elevation required is determined by the FPE you havechosen. For example, if your FPE is equal to the Base Flood Elevation(BFE), you will need to elevate your house so that the lowest floor is at orabove that elevation (see Figure 5-1). As explained earlier, if your househas been substantially damaged or is being substantially improved, yourcommunitys floodplain management ordinance or law will require thatyour lowest floor be elevated to or above the BFE.
If substantial damage and substantial improvement do not apply, you maybe able to elevate to any height you wish. But, keep in mind that raisingyour house to an elevation below BFE not only provides less protectionbut also results in little, if any, decrease in the flood insurance rate.Regardless of whether your house has been substantially damaged or is
being substantially improved, you shouldconsider incorporating at least 1 foot offreeboard into your FPE (as shown inFigure 5-1).
Elevating a house up to 3 or 4 feet abovethe existing ground level usually will nothave a great effect on its appearance andwill require only minimal landscaping andregrading. If you plan to elevate more than4 feet above the existing grade, youshould consider elevating your house a fullstory, so that you can use the space belowthe elevated house for parking, storage, orbuilding access (see Figure 5-2).
Figure 5-1As shown in thecutaway view, thelowest floor is abovethe flood level. When atleast 1 foot of freeboardis provided, only thefoundation is exposedto flooding.
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ELEVATING YOUR HOUSE
If you are elevating ahouse that has beensubstantially damagedor is being substantiallyimproved, your com-munitys floodplainmanagement ordinanceor law will not allow youto have a basement, asdefined under the NFIP.The NFIP regulationsdefine a basement asany area of the build-ing having its floorsubgrade on all sides.If your house has sucha basement, you will berequired to fill it in as partof any elevation project.Note that the NationalFlood Insurance Pro-gram (NFIP) definitionof basement does notinclude what is typi-cally referred to as awalkout-on-grade base-ment, whose floor wouldbe at or above grade onat least one side.
Figure 5-2This house in Atlanta,Georgia, was elevatedone full story. Thegarage and storagearea are at the housesoriginal elevation.
If your house has been substantiallydamaged or is being substantially improvedand is in a Coastal High Hazard Area (ZoneV, VE, or V1-V30 on the Flood InsuranceRate Map (FIRM) for your community), yourcommunitys floodplain managementordinance or law will require that the bottomof the lowest horizontal structural member(rather than the lowest floor) be elevated to or above the BFE. In manyhouses, the lowest horizontal structural member is a beam that supportsthe framing of the lowest floor. With the exception of Elevating on anOpen Foundation, described at the end of this chapter, the elevationtechniques presented in this guide are not appropriate for houses inCoastal High Hazard Areas. If you have any doubt about the type offlood hazards that may affect your house, check with your local officials.
Existing FoundationIn general, the most economical approach to elevating a house is to useas much of the existing foundation as possible. Although some elevationmethods do not allow this approach, most do. If you choose one of thelatter, a design professional must evaluate the ability of your existingfoundation to support the loads that will be imposed by the elevated houseand, as discussed in the next section, the loads expected to result from
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flooding and other hazards at the site. If changes must be made to thefoundation to increase its strength and stability, they can be made as partof your retrofitting project, but they can increase both the cost of theproject 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 canaffect the elevation process. This issue is discussed later in this chapter,in the section The Elevation Techniques.
HazardsBecause so many elevation techniques are available, elevation is practical foralmost any flood situation, but the flooding conditions and other hazards atthe house site must be examined so that the most suitable technique can bedetermined. Regardless of the elevation technique used, the foundation ofthe elevated house must be able to withstand, at a minimum, the expectedloads 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, orother hazards, a design professional should determine whether the elevatedhouse, including its foundation, will be able to withstand all of the horizontaland vertical forces expected to act on it. In making this determination, thedesign professional must consider a number of factors, including the structureand condition of the house, the soil conditions at the site, the proposedelevation technique, and the hazards at the site. The conclusion may be thatadditional modifications must be made during the retrofitting project.
AccessElevating a house usually requires that new means of access be provided.For example, if your entry doors were originally at ground level, newstaircases, elevators, or ramps will have to be built. When an attachedgarage is elevated, providing access for vehicles may require changes toportions of your lot, such as building a new, elevated driveway on earth fillthat ties into high ground elsewhere. This solution can be practical when theamount 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 considerelevating your house a full story so that you can use the lower level forparking and avoid the need for an elevated driveway.
The need to provide new means of access is often the main objection thathomeowners have to elevating. But functional and attractive solutions tothis problem can usually be developed, as shown in Figure 2-2 in Chapter 2and Figure 5-3.
WARNINGPlacing fill in floodwaysand Coastal High Haz-ard Areas is normallyprohibited. Check withyour local officials aboutState and local require-ments concerning theuse of fill.
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ELEVATING YOUR HOUSE
House Size, Design, and ShapeIn general, the larger the house and the more complex its design andshape, the more difficult it will be to lift on jacks. Multistory houses aremore difficult to stabilize during