Laserfiche WebLink
Floodplain Information Sheet 3 <br />Floodplain Management Series <br />• A structure built before the publication date of your community's first FEMA floodplain map (pre -FIRM) is <br />"grandfathered" with the following conditions: <br />— A structure may continue to be used, repaired, and maintained, but additions must be elevated or properly flood -proofed <br />in compliance with current community regulations. <br />— If a structure is damaged (e.g., by fire, flood, tornado) by more than 50 percent of the pre -damage value or if the <br />cumulative additions and improvements are more than 50 percent of the original structure's inflation -adjusted value, <br />the entire structure would have to be reconstructed to comply with the community's floodplain regulations (thus <br />losing "grandfather" status). <br />What are the key building standards for residential structures in flood fringe? <br />If possible, build outside the floodplain, with your lowest floor (including basement) above the regulatory flood protection <br />elevation (RFPE). This reduces your risk of flooding, and you will not be required to buy flood insurance. Also, if you <br />build outside the high flood risk zone (the 1-percent chance or 100-year flood zone), preferred risk policy (PRP) flood <br />insurance is available at a significantly reduced premium. <br />If you must build in the flood fringe, work with your community to ensure that all local regulations are addressed in your <br />proposed building plan. NOTE: Local ordinances may be more restrictive. <br />The key building standards that meet state and federal law (Figure 1) include: <br />• No placement of fill is permitted in the floodway. <br />• Top (i.e., walking surface) of the lowest floor (including basement or crawl space) is at or above the RFPE. <br />• Fill is at 100-year flood elevation plus floodway stage increase, or higher, extending at least 15 feet horizontally from all <br />sides of the structure. <br />• An "as built" survey is submitted to the zoning authority to verify that the development was built at the permitted <br />elevation. <br />• Must meet all local ordinance requirements, including setback* requirements (i.e., from lot lines, and for shoreland man- <br />agement or wild and scenic rivers ordinances). Many communities also require that the access (driveway and access roads) <br />elevation is no lower than 2 feet below the RFPE. <br />*Setbacks are typically measured from the ordinary high-water (OHW) level, which is the top of the bank of the channel on watercourses. The OHW is <br />not the same as the 100 year floodplain elevation, serves a different purpose, and is usually at a lower elevation. <br />RFPE Formula <br />100 year flood elevation <br />+ stage increase due to floodway <br />+ freeboard (state requires 1 foot minimum) <br />= regulatory flood protection elevation (RFPE) <br />>15 ft <br />1 foot <br />freeboard <br />(minimum} <br />Flood Fringe <br />Elp <br />▪ 1% annual chance flood elevation <br />(including stage increase) <br />OHW <br />Equivalent Terms and Definitions <br />Base Flood Elevation (BFE) — Same as the 1 percent <br />annual chance flood elevation or the "100-year" flood <br />elevation. <br />Regulatory Flood Protection Elevation (RFPE) — The <br />RFPE is the 100-year flood (1 percent annual chance <br />flood) elevation + stage increase due to establishing <br />floodway + freeboard (Minnesota's minimum is 1 foot). <br />The lowest floor must be elevated so that the walking <br />surface of that lowest floor is at the RFPE or higher. <br />11--Floodway-10. <br />Figure 2. Key standards for <br />structures in the flood fringe <br />(picture not drawn to scale). <br />Contact: DNR Ecological & Water Resources in St. Paul (651) 259-5700 <br />http://mndnr.gov/waters <br />Page 2 <br />February 2011 <br />