Elevate the building on fill

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, on columns, and on piles. Two variations to achieve elevation are: on engineered fill (as described here) 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 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 looking to elevate on fill, be aware there may be state or local regulations that prohibit fill anywhere in the floodplain.

Structures located within Coastal V Zones cannot be elevated on fill. Elevation on fill is only appropriate for structures located outside of Coastal V Zones with shallow to moderate flood depths and low to moderate flood velocities. The property on which the structure sits must have enough access for the equipment to install the fill and enough space between their lot and surrounding lots to avoid impacting flooding on neighboring properties. This elevation technique, also known as landraising, is most suitable for rural areas due to the amount of fill required to elevate the building and the area required for the side slopes of the fill material.

As with most elevation techniques, when elevating on fill, 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 construction equipment? Is it worth the expense of lifting? If the proposed project moves forward, and once necessary permits are acquired, the structure is then temporarily moved aside while the existing foundation is removed and compacted clean fill material is placed to a height that lifts the building above the Base Flood Elevation.

The placement of the fill material should be in compliance with all aspects of the National Flood Insurance Program (NFIP) and not cause adverse impacts to adjacent properties by increasing flood height or flood velocities. Once the fill material has been placed, the structure is reinstalled on the new foundation. Additionally, the fill can be covered in grass or other vegetative cover to help guard against erosion.

An annual inspection of the entire site is recommended in order to ensure that the fill material is showing no sign of erosion, particularly around the foundation of the structure and the side slopes, where floodwater could cause erosion.

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 assist in evaluating the building and building site for the feasibility of undertaking 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, then construct permanent access. All utilities and plumbing will be reconnected.
7. New landscaping can be conducted by contractor or owner.

Special Considerations:

• This mitigation option type is not recommended within the regulated floodway or 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 or if your proposed fill site is located in the floodway, 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 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 less than fair 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.