Permanently elevating a building by placing it on columns involves temporarily lifting the structure and installing wood, steel, or precast reinforced concrete columns into pre-dug holes. The columns are typically anchored or embedded into concrete pads to accommodate any large loads. Bracing the columns may be required to help the columns act as a unit and to resist horizontal loads, such as wind.
Elevating a building on piers is similar to elevating a building on columns. Piers are typically constructed of reinforced concrete or concrete masonry units (CMU), and they are supported by concrete footings. Piers are a little different from columns in that they act individually, and care must be taken to ensure that the piers can sustain both the necessary vertical loads from the building and horizontal loads caused by flooding.
For floodwaters deeper than six feet or for buildings that experience higher wind velocities/stronger floodwater flows, a building should be elevated onto piles. The piles, which are driven into bedrock or driven deep enough to develop the necessary friction forces, are constructed of wood, steel, micro-piles, or reinforced concrete. There does need to be sufficient space around the building to accommodate the construction machinery required to drive the piles.
The main advantages of elevating a building on columns/piers/piles are that the building has complete protection from flood risk, the building remains in its original location, and the construction methods are fairly simple and well established.
Some of the disadvantages include the building’s appearance is altered, as well as its relationship to the ground, and the vertical access to the building is changed, which will require constructing new stairs, ramps, and/or an elevator.
- For floodwaters deeper than six feet or for buildings that experience higher wind velocities/stronger floodwater flows, a building should be elevated onto piles.
- A geotechnical investigation must be performed to determine if the soil under and around the building is susceptible to erosion and/or appropriate for this type of construction.
- Lighter (i.e. wood frame) and smaller structures are easier and less expensive to elevate, although more robust and larger structures can also be elevated.
- Masonry structures that are elevated on columns/piers may be more susceptible to cracking.
- Before construction begins, it is important to determine if the land beneath your building has the potential to yield archaeology that is important to history or prehistory.
- Southern Tier Central Regional Planning and Development Board: www.stcplanning.org/usr/Program_Areas/Flood_Mitigation/Floodproofing/FProof_02_Elevate.pdf
- FEMA’s Foundation Requirements and Recommendations for Elevated Homes: www.fema.gov/media-library-data/1386073605870-56034eb27952e04bd44eb84b72032840/SandyFS2OpenFoundation_508post2.pdf
- Floodlists’s Elevation of Buildings in Flood-Prone Locations: floodlist.com/protection/elevation-buildings-flood-prone-locations