Allentown, PA Environmental Rules: Flood Elevation Requirements (2026)

Chapter 298's definitions section, § 298-9, defines REGULATORY FLOOD ELEVATION as "the base flood elevation (BFE) or estimated flood height as determined using simplified methods plus a freeboard safety factor of 1 1/2 feet," and specifies that "the freeboard safety factor also applies to utilities and ductwork." BASE FLOOD ELEVATION itself is defined as the water surface elevation shown on the FIRM for Zones AE, AH and A1-30 for a flood with a 1% or greater annual chance of occurring.

Section 298-27 applies that regulatory flood elevation to construction. For residential structures in AE, A1-30 and AH Zones, any new construction or substantial improvement must have the lowest floor, including any basement, elevated up to or above the regulatory flood elevation; in A Zones lacking mapped base flood elevations, the lowest floor must instead reach the regulatory flood elevation as determined under § 298-22C, which can default to three feet above the highest adjacent grade absent better data. In AO Zones, the lowest floor must sit at or above the highest adjacent grade, at least as high as the depth number on the FIRM. Nonresidential structures follow the same elevation standard or may instead be floodproofed watertight below the regulatory flood elevation, with an engineer's or architect's certification and, for floodproofed buildings, an annual inspection and maintenance plan plus a flood emergency operation plan filed with the Floodplain Manager before a certificate of occupancy issues.

Section 298-27C flatly prohibits basements in the floodplain and requires any fully enclosed space below the lowest floor to have flood vents equalizing hydrostatic pressure, at least two openings totaling one square inch per square foot of enclosed area, with opening bottoms no higher than one foot above grade. Accessory structures are exempt from elevation but must keep power lines and wiring raised to the regulatory flood elevation and stay under 200 square feet, or a variance is required.