ELEVATION OF BUILDING ON PILES
INSIDE THE FLOODPLAIN

What Is It?

Cost: Expensive and site-dependent. 5-25% additional cost for new construction, Elevating a detached 1-2 family home can range from $45,000 to $200,000. Costs stem from pile-driving/new foundation, wet floodproofing measures, relocation of mechanical/electrical systems, and addressing potential accessibility issues from elevation in urban areas. Elevating existing buildings may require addressing other building code issues prior to elevation. Costs may be offset by reductions in insurance rate.
Applications: Existing buildings can be elevated, though at greater cost than building into new construction. May not be practical or cost effective for large commercial buildings.

Elevating a building on fill cannot protect a building from wave forces and cannot be used in V zones. Elevating a building on piles provides wave force protection and is mandatory in V zones[1] for all new construction and in retrofits for bringing the building into compliance with FEMA standards. It is a strategy best pursued for new construction. Elevating a building on piles will allow floodwaters to pass underneath the building without causing structural damage. The space underneath the building cannot be occupied except for use as parking, storage, or building access. This space may be open or closed but should be wet floodproofed if enclosed, and breakaway walls or lattice walls should be used for the enclosure. Vents can be installed into breakaway walls to allow for pressure equalization to prevent the walls from failing until the water is deep enough for significant wave action. As with elevating a building on fill, elevating a building on piles can significantly reduce flood insurance premiums.

While elevating a building on piles above flood elevation provides effective protection for buildings, it is costly and infeasible for larger buildings. Piles must be driven into the ground, and the building must be separated from its foundation while piles or a new foundation are constructed below. Because many existing buildings in the Northeast are old, addressing asbestos, lead paint, and structural issues related to elevating heavy mechanical/electrical systems may increase costs significantly. Larger buildings with subgrade basements will face significant difficulties in elevating. Accessibility issues from elevation may increase costs. In A zones[2], it will likely be more cost-effective for many non-residential buildings to use dry floodproofing. However, in V zones, the lowest occupied floor will need to be above base flood elevation.

Benefits

  • Protects a building from high-velocity flooding and wave action.
  • Site elevation may reduce flood insurance premiums. Site may even potentially be removed from flood zone. Elevation of large residential/non-residential with basement/enclosure/crawlspace from base flood elevation to 3 feet above base flood elevation may reduce annual insurance rates by over 70%.

Drawbacks

  • Creates additional space below the elevated structure that can be used for storage and parking. Elevation of existing buildings may maintain building floor area.
  • Elevation of the building site in urban areas can create accessibility issues and have negative impacts on the streetscape and adjacent sidewalks.
  • Very expensive to retrofit.
  • Infeasible for larger buildings.
  • Elevation may disrupt urban aesthetic without additional measures.

Regulatory Impacts and Requirements

  • Mandatory for all new construction in V zones. Elevating a building on piles is the only retrofit option that will bring an existing residential structure into compliance with FEMA standards in V zones.

Financing Options, Incentives, And Rebates

Additional Resources

Project Examples

  • Harris Home: Home elevated post-Katrina resulting in reduced flood insurance premiums

SAMPLE OF SUPPLIERS

  • General building contractors

SOURCES

Photo credit: FEMA, Picture is part of the Public Domain

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

[2] Defined by FEMA as an area subject to inundation by the 1-percent-annual-chance flood event.