ELEVATION OF BUILDING ON FILL
INSIDE THE FLOODPLAIN

What Is It?

Cost: Expensive and site dependent. 5%-25% additional cost for new construction. The fill itself is a major additional cost associated with this measure. Additional site landscaping costs can be built into design of new buildings. Building accessibility issues from elevation in urban areas may also add additional costs. A retaining wall may also be necessary. Costs may be offset by reductions in insurance rate.
Applications: Due to extensive site modification, much more suitable for new construction.

Elevating a building above base flood elevation (BFE) is an effective way to provide protection from storm-related flooding, as well as flooding from high tide due to sea level rise. A building can be raised above base flood elevation by using fill to elevate the building or to reshape the entire building site’s topography. Due to the significant modifications needed to bring the building site above BFE, elevating a building on fill is much more difficult for retrofits. Proper elevation of a site may provide reductions in flood insurance premiums—or even entirely remove the site from the flood zone by obtaining a letter of map revision.

While elevating a building site above BFE will provide protection from some flooding, it will not protect the site from wave action, which may scour the fill. As a result, FEMA does not permit the use of structural fill in V zones.[1] Elevation of sites over three feet is not recommended, as channelization can occur and flooding of adjacent, lower areas could be exacerbated. Proper assessment and mitigation of potential negative effects on the surrounding area as a result of site elevation should be considered. If the building site is not completely elevated over BFE, additional floodproofing measures can be utilized to maximize flood protection. A significant portion of the additional cost of elevating a building on fill stems from the fill itself. Use of recycled materials in the fill can help to reduce costs.

Benefits

  • Protects a building from flooding by raising it above BFE.
  • Site elevation may reduce flood insurance premiums. Site may even potentially be removed from flood zone. Elevation of a large residential or non-residential building with a basement, enclosure, or crawlspace from BFE to 3 feet above BFE may reduce annual insurance rates by over 70%.
  • If entire building is raised above flood elevation, building area can be preserved.

Drawbacks

  • Drainage and implications of site elevation on adjacent sites may prevent elevation of the site on fill. Additional costs related to assessing drainage and impacts on adjacent sites will be necessary.
  • Elevation of the building site in urban areas can create accessibility issues and have negative impacts on the streetscape and adjacent sidewalks.
  • The use of fill and potential need for a retaining wall will add significant costs to a new construction project.

Regulatory Impacts and Requirements

A summary of potential regulatory touchpoints follows:
Elevation-of-Building-on-Fill

  • FEMA does not permit elevation of building sites on fills in V zones.

Financing Options, Incentives, And Rebates

Additional Resources

SAMPLE OF SUPPLIERS

  • General building contractors

SOURCES

Photo credit: City of New York- Department of Sanitation, Public Domain

[1] Defined by FEMA as an area along coasts subject to inundation by the 1-percent-annual-chance flood event with additional hazards associated with storm-induced waves.