Section R402 addresses construction requirements for buildings in areas at risk of flooding. Flood elevation is the maximum elevation expected to be reached by a 100-year flood (flood with 1 percent annual probability). Buildings must be elevated or floodproofed to be above the flood elevation plus freeboard (additional height for safety margin). Elevation typically requires that the lowest floor, including basement, be above flood elevation. Crawlspace buildings may allow wet floodproofing where water is permitted to enter, with proper drainage and drying provisions. Wet floodproofing buildings allow water entry but protect utilities and structural integrity. Elevation is commonly achieved by raising buildings on posts or piers, with appropriate connections resisting flotation and lateral forces. Mechanical systems including furnaces and water heaters must be elevated above flood elevation. Electrical systems must be protected from water damage or also elevated.