|Image from the NFIP bulletin on Historic Structures|
For non historic houses in communities that participate in the flood insurance program, once the house has been "substantially improved", meaning 50% of its pre improved value, it must be brought into conformance with the National Flood Insurance Program requirements. Note that in many places, "substantial improvement" is cumulative (though not in Massachusetts), so if you renovate your kitchen this year, and upgrade the heating system next year, and re-do the bathrooms in a couple of years, these all count together towards reaching the 50% improvement level.
These images from FEMA's bulletin help to visualize what is required to bring a structure into compliance once it has undergone "substantial improvement" or flood losses worth 50% or more of the value of the home.
However, a structure that meets FEMA's criteria for being a "Historic Structure" is not included in the 50% substantial improvement rule as long as changes or improvements do not result in a loss of the structure's historic designation.
This excerpt is from the following bulletin:
National Flood Insurance Program (NFIP) Floodplain Management Bulletin: Historic Structures
The National Flood Insurance Program (NFIP) gives special consideration to the unique value of one of our Nation’s most significant resources – its historic buildings, landmarks, and sites. It does so in two ways.
First, the NFIP floodplain management regulations provide significant relief to historic structures. Historic structures do not have to meet the floodplain management requirements of the program as long as they maintain their historic structure designation. They do not have to meet the new construction, substantial improvement, or substantial damage requirements of the program. This exclusion from these requirements serves as an incentive for property owners to maintain the historic character of the designated structure (44 CFR §60.3). It may also serve as an incentive for an owner to obtain historic designation of a structure.
Secondly, a designated historic structure can obtain the benefit of subsidized flood insurance through the NFIP even if it has been substantially improved or substantially damaged so long as the building maintains its historic designation. The amount of insurance premium charged the historic structure may be considerably less than what the NFIP would charge a new non-elevated structure built at the same level. Congress requires that the NFIP charge actuarial rates for all new construction and substantially improved structures (National Flood Insurance Act of 1968, 42 U.S.C. 4015).
*changes in 2012 have eliminated this subsidy and a phased increase will bring all structures up to unsubsidized levels for flood insurance.
Does it make sense to incorporate mitigating building criteria to make an historic home more resilient in the event of flooding? You bet! There are many suggestions to help make your historic home better able to withstand flooding (outlined in the NFIP bulletin on Historic Structures). But already, mis-information has resulted in antique homes being demolished because the owner perceives the substantial improvement rule to be too much of a hardship. Historic Homes are unique in their construction and cultural value and FEMA has allowed for them to receive special consideration. This can make the difference in whether an owner decides to preserve a historic home.
So what makes a house "historic"? According to FEMA's bulletin:
So you don't have to be individually listed on the National Register, your house can be listed as a contributing member in a National Register Historic District (like the Old King's Highway). Or your house could be listed on the state listing of historic places (for Massachusetts, this is MACRIS). Or, your house could be designated on a local inventory for communities with historic preservation programs (like your local historical commission which is an arm of the State's Historical Commission).
If you live in an AE zone or V zone, this is welcome news indeed!
For more info on substantial improvement requirements:
NFIP Substantial Improvement/Substantial Damage:Requirements and Definitions