Elevate the building on posts or columns

Overview

Elevation is a mitigation technique in which a structure, existing or new, is raised high enough that the lowest floor and all plumbing, electrical systems, and ductwork are at or above the Design Flood Elevation to prevent floodwaters from damaging the structure and its contents. There are generally five types of elevated foundations: on extended solid perimeter foundation walls, on piers, on posts or columns (as described here), and on piles. Two variations to achieve elevation are: on engineered fill or by abandoning the lowest interior floor.

Depending on your structure’s foundation, location, and other factors, such as the likelihood of other hazards occurring, one elevation type might be a more effective strategy to protect your structure – and pocketbook – than another. The community’s floodplain management ordinance and local zoning codes should be consulted when deciding to what height to raise the structure, as additional elevation above the Base Flood Elevation may be required by local regulations. If you need to raise your structure more than four feet, you might consider raising it a full story for additional protection, temporary storage, parking, and/or aesthetics. (Note that all portions of the building below the elevated first floor must be made of flood-resistant materials and cannot be used as living space – only for storage and access.)

Posts and columns are types of open foundation systems in which the building is raised in such a way that water flows under the building. They can be made of wood, steel, or precast reinforced concrete. They are most appropriate for homes that experience flooding of moderate depth and velocity, without debris or ice flow.

As with most elevation techniques, when elevating on posts or columns, the first step is to have the structure and the land on which it sits evaluated by a registered design professional for feasibility of success. Key questions are: Will it survive the lifting process? Is there enough space for the necessary equipment? Is the soil type appropriate for the type of post or column desired? Is it worth the expense of lifting?

If the project moves forward, and once necessary permits are acquired, the structure is then lifted off of its foundation to the appropriate height and secured using temporary supports while the existing foundation is removed and the posts or columns are installed. Posts and columns are typically placed into pre-drilled holes, backfilled around, and anchored by a concrete pad or footing to support and transfer the weight of the structure to the ground below. They often require bracing to prevent the structure from swaying, also known as lateral movement. Once the posts or columns are in place, the structure is lowered and secured with bracing and appropriate fasteners. All areas below the lowest habitable floor must remain unfinished and be restricted for use as vehicle parking, storage, and/or building access. If the area is enclosed, everything below the Base Flood Elevation must be wet floodproofed with flood vents or, if you live in a coastal high hazard area, the walls must be breakaway walls with flood openings.

An annual inspection of the posts or columns and all fasteners is recommended in order to ensure that cracking, corrosion, or failure is not occurring.

Next Steps:

1. Consult with your local floodplain manager to determine the height to which you should elevate and what permits are necessary.
2. Hire a registered design professional to evaluate the building and building site for the feasibility of the project.
3. Hire a professional house moving company to design your new foundation, provide details on the elevation process, and obtain required permits from your community’s building department.
4. The house mover will work with utility companies to disconnect all utilities and plumbing prior to elevating the building.
5. The house mover will remove obstructive landscaping, stairs, and landings, then temporarily elevate the building while the new foundation is constructed.
6. The house mover will lower the building onto the new foundation, secure it, and then construct permanent access. All utilities and plumbing will be reconnected.
7. Once the structure is elevated, new stairs, porches and landscaping can be added, if necessary.

Special Considerations:

• This mitigation option type is not recommended in areas with high velocity flooding, where water moves at more than 6 feet per second. If you do not know the projected flood velocity around your property, check with your local floodplain manager.
• Costs and difficulty increase as the dimensions and weight of the structure increase and impact the structure’s stability. Slab-on-grade structures are particularly risky to elevate as they have a much higher likelihood of failing and require additional steps to evaluate the likelihood of success and to complete the elevation process (see FEMA P-312 page 5-9 for more information). Any additions to a structure (exterior façades, attached garages, porches, wings, additions, and chimneys) must either be removed and lifted separately or braced to stay in place. The easiest type of structure to elevate is one that is single-story, rectangular, and wood-frame with a crawlspace; the hardest is one that is multi-story and masonry with a slab-on-grade foundation.
• If the existing building considered for elevation has a crawlspace or basement, the crawlspace or basement would need to be emptied of utilities and mechanical equipment, filled with sand, gravel, or soil and capped with concrete or a vapor barrier. Any removed utilities or mechanical equipment would then be relocated above the design flood elevation, which is often a small addition to the structure.
• You may be required to sign a non-conversion agreement stating any enclosed areas below the BFE will remain unfinished and restricted to specific limited use (i.e. vehicle parking, limited storage, and building access), and acknowledging that the restrictions have been recorded on the deed to the property; since the deed follows the property, future homebuyers will be informed of the restrictions.
• If your building or structure is in less than fair condition, this mitigation option type is not recommended. The only mitigation option types recommended for structures in fair to poor condition are acquisition, demolition, and the purchase of flood insurance or business interruption insurance.
• Ensure compliance with all applicable National Flood Insurance Program (NFIP) requirements and local building codes. The NFIP sets minimum standards and allows individual communities to adopt their own additional or more stringent requirements via local floodplain management ordinances, regulations, and laws.
• If your building sustained substantial damage during a recent flood event, you may be required to bring it into compliance with NFIP and local floodplain management regulations.
• Be careful not to redirect water flow from your property onto another property. No adverse impact (NAI) floodplain management is an approach that ensures the action of any property owner, public or private, does not adversely impact the property and rights of others. NAI calls for any adverse impact caused by a project to be mitigated as part of the project. By following NAI principles, you can: prevent flooding from increasing or damaging others; see a reduction in flood losses over time; and avoid challenges and lawsuits over causing or aggravating a flood problem.
• Contact a local flood insurance representative to learn more and get a quote, if you do not already have flood insurance. (Most homeowner’s insurance policies do not cover flood damage.)
• Renters and those who own specific types of property may be limited in which mitigation options they can undertake or have different requirements to which they must adhere. If you are a renter or own any of the following listed property types, click through to learn more: Renter; Unit in a multifamily residence; Manufactured home; Farm/ranch; Historic property; New construction.