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Data updated October 22, 2026

Data updated October 22, 2026

Zone AH flood zone: shallow ponding with a base flood elevation

Updated October 22, 2026

Zone AH is a Special Flood Hazard Area where the 1% annual chance flood is shallow, averaging 1 to 3 feet deep, usually as ponding, and where FEMA has set a base flood elevation. Flood insurance is required for federally backed mortgages.

Zone AH is FEMA’s label for shallow flooding that collects in low areas. The 1% annual chance flood there is expected to average 1 to 3 feet deep, and the Flood Insurance Rate Map (FIRM) shows a base flood elevation (BFE), a single water surface elevation for the ponded area.

What Zone AH means

44 CFR 64.3 defines Zone AH as “Areas of special flood hazards having shallow water depths and/or unpredictable flow paths between (1) and (3) feet, and with water surface elevations determined.” 44 CFR 59.1 groups AH with AO and VO as an “area of shallow flooding”: a 1% or greater annual chance of flooding to an average depth of 1 to 3 feet “where a clearly defined channel does not exist,” characterized by ponding or sheet flow.

FEMA’s shallow flooding mapping guidance (December 2020) describes Zone AH as usually ponding, or sheet flow on uniformly sloping terrain, with BFEs from the hydraulic analysis shown on the map. Ponding is runoff that collects in a depression that may have no outlet. Where average depths are under 1 foot, the guidance maps the area as shaded Zone X instead.

Zone AH is part of the Special Flood Hazard Area (SFHA), with Zones A, AE, AO, AR, A99, V and VE.

Is flood insurance required in Zone AH?

Yes. 44 CFR 64.3(b) lists AH among the zones where “mandatory purchase of insurance is required.” Under 42 U.S.C. 4012a, federally regulated lenders, Fannie Mae and Freddie Mac, and federal agencies providing financial assistance may not make or buy a loan secured by a building in the SFHA, in a community where NFIP coverage is available, unless the building is insured for the term of the loan. Coverage must equal at least the lesser of the outstanding principal or the NFIP maximum. See flood insurance requirements.

Building rules in Zone AH

44 CFR 60.3(c) treats AH like Zone AE for elevation. For new construction and substantial improvements, a participating community must require:

  • Residential buildings with the lowest floor, including basement, elevated to or above the base flood level (60.3(c)(2)).
  • Nonresidential buildings elevated to that level or made watertight below it, with a professional certification (60.3(c)(3) and (c)(4)).
  • Enclosed areas below the lowest floor used only for parking, access or storage, with openings that let floodwater in and out (60.3(c)(5)).
  • Manufactured homes elevated to or above the BFE and anchored (60.3(c)(6) and (c)(12)).
  • Adequate drainage paths around structures on slopes, to guide floodwater around and away from them (60.3(c)(11)). This rule applies only in Zones AH and AO.

These are federal minimums (“minimum standards” in 60.3’s words), so check the local floodplain ordinance and building code as well.

What Zone AH means for insurance cost

FEMA states that the NFIP’s pricing approach under Risk Rating 2.0 “does not use flood zones” to determine flood risk. Premiums are based on flood frequency, flood types including heavy rainfall, distance to water, elevation and rebuilding cost. The zone still decides whether the federal purchase requirement applies. Because AH areas have a BFE, an Elevation Certificate can document how far a building’s lowest floor sits above or below it.

How to check a parcel’s zone

Search the address on FEMA’s Flood Map Service Center for the effective FIRM and any Letters of Map Change. If a structure on natural ground is higher than the BFE, a Letter of Map Amendment can remove it from the SFHA.

Zone AH in Miami-Dade County

Zone AH is the most common high-risk zone in Miami-Dade. Of the about 551,600 buildings in Miami-Dade’s 80 ZIP code areas (78 with reports), 116,121 (21%) have their centroid in Zone AH on the effective FIRM, more than in Zone AE (99,269). The figures come from placing FEMA/ORNL’s USA Structures inventory on a July 2026 snapshot of FEMA’s National Flood Hazard Layer. AH dominates in the western suburbs and the south of the county:

New FIRMs for Miami-Dade take effect on February 19, 2027, under FEMA’s final flood hazard determination published October 14, 2026 (91 FR 65238). BFEs and zone limits can change on that date.

Questions

Is Zone AH a high-risk flood zone?

Yes. Zone AH is part of the Special Flood Hazard Area, the land FEMA maps as having a 1% or greater chance of flooding in any year. The expected flooding is shallow, averaging 1 to 3 feet.

Is flood insurance required in Zone AH?

Yes, for buildings secured by loans from federally regulated or insured lenders, loans bought by Fannie Mae or Freddie Mac, and other federal financial assistance, in communities that participate in the NFIP.

What is the difference between Zone AH and Zone AO?

Both are shallow flooding zones with average depths of 1 to 3 feet. Zone AH shows a base flood elevation and usually represents ponding; Zone AO shows a flood depth in feet above ground and usually represents sheet flow on sloping terrain.

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