Buoyant Foundations - Not ready for prime time!

Patricia Skinner  |  9/29/2007 7:49:37 AM

Buoyant foundation on the bayou.

The buoyant foundation, floating-house concept for avoiding flood damage has been around for many years and is practiced widely in the Netherlands. There are examples as well in south Louisiana, just as there are examples of homeowner-designed and constructed personal levees, floodwalls and other flood-protection devices. These systems are generally employed to protect older buildings where flooding became a problem long after the building was constructed. The protection they provide is not recognized by the National Flood Insurance Program. (You get no premium discount and likely will not be able to buy a policy.) These systems, including buoyant foundations, cannot be used as an alternative to elevation for new construction, for buildings that have been substantially damaged or for buildings that are being substantially improved.

You should expect your local permit office to deny a permit application for building or substantially improving a residential or non-residential building in a special flood hazard area on a buoyant foundation. Even if the building is to be built at the required elevation, granting a permit for buoyancy would involve waiving the anchoring requirement of the flood ordinance and possibly of the wind provision of the building code. The potential penalties for routinely waiving requirements would be felt by the community and its residents.

Minimum Flood-Related Requirements for Foundations in Flood Hazard Areas

The minimum requirements of the community's flood-damage prevention ordinance for new construction in flood hazard areas are a) that the lowest floor be at or above the flood-protection elevation and b) that the building be "designed, constructed and anchored to prevent flotation, collapse and lateral movement resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy." If the elevation requirements are met, the ordinance provision related to anchoring would have to be waived in order for a buoyant foundation to be permitted. Since anchoring is required for wind uplift resistance, not just to prevent flotation, the waiver could have broader implications and consequences for building safety and insurability.

Repairs and remodeling must meet the current requirements for new construction when the original building is subject to an elevation requirement because the damage or improvement is substantial.
  • A building is substantially damaged if the cost to restore the building to its pre-damaged condition would be 50% or more of the pre-damage value of the building. Some communities lower the 50% threshold to 40% or lower.
  • A building is being substantially improved if the cost of the improvement is 50% or more of the pre-improvement value of the building. Some communities lower the 50% threshold to 40% or lower.

When is a buoyant foundation a violation?

A buoyant foundation would be a violation in your community when either of the following is true:

  1. Your local government has adopted specific ordinances banning their use.
  2. The building or construction activity is required to meet the wind uplift provisions of building codes or the elevation and anchoring provisions of the flood-damage prevention ordinance.

The second is always true for new construction and repair of a substantially damaged or substantially improved building in a special flood hazard area. It is sometimes a requirement for remodeling. The specific floodplain regulations that apply to remodeling and additions depend on the flood zone designation (A or V) and the type and cost of improvement.

These are some buildings and projects that are required to meet the locally adopted flood-damage standards that apply to new construction:

  • Substantial vertical additions in A and V zones: The entire building must meet the requirements for new construction (i.e., the entire building would have to be elevated and anchored).
  • Substantial lateral additions in V zones: The existing building and its addition must be elevated and anchored.
  • Substantial lateral additions in A zones: Only the addition must be elevated and anchored, provided that no remodeling is done in the existing portion of the building other than cutting an opening to allow passage between the building and its addition.

For non-substantial lateral additions to a post-FIRM structure in A and V zones, the addition must meet the elevation requirements that were in effect when the building was built. The required elevation may be lower than the current elevation requirement in that area.

Flood-damage ordinances apply to additions even when the state or local government exempts additions from other residential building codes. The flood requirements were in effect prior to the state's adoption of the International Residential Code and related codes and remain in effect regardless of changes to interpretation and implementation of those codes.

When is a buoyant foundation not a violation?

The compliance of buoyant foundations with all aspects of the International Residential Code (as adopted by the state of Louisiana) has not been investigated. There may be electrical, plumbing, energy or other provisions that would have to be waived if buoyancy were added to the foundation. However, the non-compliance of buoyant foundations with the flood-damage provisions of the code -- and with the flood damage prevention ordinance adopted by each community -- is clear. A buoyant foundation is not a violation of the flood ordinance ONLY when the building or construction activity is not required to meet the flood-damage prevention elevation and anchoring requirements for new construction and substantially improved structures.

These are some buildings and projects that are NOT required to meet the locally adopted flood ordinance elevation and anchoring requirements:

  • An existing Pre-FIRM building that is not substantially damaged.
  • An existing Pre-FIRM building that is not being substantially renovated or improved.
  • An existing Pre-FIRM building that is having a non-substantial addition. If the building is Post-FIRM and subject to elevation requirements when originally built, the addition must be elevated to that original height, even if it is not a substantial improvement.
  • A building that is not being built in an identified flood hazard area (an A or V zone), unless the community has added the building location to its regulatory floodplain and is managing that area as a special flood hazard area. (A common example is adoption of ABFEs).

Don't get your hopes up!

Widespread media coverage of student work at LSU may have created unrealistic expectations for many people who yearn to return, restore and rebuild in south Louisiana. This buoyant foundation technique, however attractive, is not a legal alternative to meeting elevation requirements in the flood damage prevention ordinance and in the International Building Code. Additional study and experimentation with buoyant foundations, such as that going on at LSU and in other academic settings, may lead some day to an acceptance of these foundations and a recognition of buoyant foundations as code-compliant construction. At this time -- and for the foreseeable future -- buoyant foundations do not meet the minimum code requirements for construction in flood hazard areas. Whether a buoyant foundation would meet the minimum code requirements for building outside the special flood hazard area has not been determined.

If the cost of adding a buoyant foundation does not meet the substantial improvement threshold in your community, there may be nothing in the law to prevent you from experimenting with buoyancy on your existing Pre-FIRM home -- especially if that home was not built under any building code. Check with your local permit office.

At this time, and without more study, buoyancy is not recommended as a method of protecting homes from floods that exceed the elevation to which they have been built. Building at higher elevations and using flood-damage resistant materials and methods below and above the elevation of the first floor remain the better options.

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