The 9th Edition of 780 CMR requires existing buildings to comply with the Flood Load requirements of Section 1612 if the building is undergoing substantial improvements, is being restored due to substantial damage, or is undergoing a substantial repair of a foundation. Section 1612.1 reads as follows:
1612.1 General. Within flood hazard areas as established in section 1612.3, all new construction of buildings, structures and portions of buildings and structures, including substantial improvement and restoration of substantial damage to buildings and structures, and substantial repair of a foundation shall be designed and constructed to resist the effects of flood hazards and flood loads. For buildings that are located in more than one flood hazard area, the provisions associated with the most restrictive flood hazard area shall apply.
Substantial improvement, substantial damage, and substantial repair of a foundation are defined in Chapter 2 of 780 CMR and by Federal Regulations. Substantial improvement is work that equals or exceeds 50% of the market value of the building before the improvement is started. Substantial damage is damage of any origin that requires restoration to the building to its before-damaged condition that would equal or exceed 50% of the market value of the building before the damage occurred. Substantial repair of a foundation includes work to repair or replace 50% or more of the perimeter along the base of the foundation measured in linear feet, or repair or replacement of 50% or more of the piles, columns or piers of a pile, or column or pier supported foundation.
If compliance is required, the existing building must comply with 780 CMR and the 2014 Edition of ASCE 24. Note that the 9th Edition of 780 CMR amends the definition of Design Flood Elevation to be the same as Base Flood Elevation.