Flood Risk Is a Site Constraint That Affects Siting, Foundation, and Code Compliance
Floodplain development is one of the most tightly regulated aspects of building design. Federal, state, and local floodplain management regulations restrict what can be built in flood-prone areas and how buildings must be constructed to protect occupants and property. The ARE PA exam tests candidates' understanding of flood zone classification, base flood elevation, and the constraints that flood-prone sites impose on building design.
FEMA Flood Insurance Rate Maps (FIRMs)
The Federal Emergency Management Agency (FEMA) produces Flood Insurance Rate Maps (FIRMs) that identify flood hazard areas across the United States. These maps are the primary reference for floodplain analysis in architectural practice. Key concepts from FIRMs:
- Special Flood Hazard Area (SFHA): The land area subject to inundation by the 1% annual chance flood (the 100-year flood). Shown on FIRMs as Zone A (approximate) or Zone AE (detailed analysis with established BFE).
- Base Flood Elevation (BFE): The computed elevation to which floodwater is expected to rise during the 100-year flood event. BFE is the benchmark elevation for flood-resistant construction requirements.
- Floodway: The channel of a river or stream and the adjacent land area that must be reserved to discharge floodwaters. Development in the floodway is the most severely restricted.
- Floodway Fringe: The area between the floodway and the boundary of the 100-year floodplain. Some development is permitted with mitigation measures.
- 500-year Floodplain (Zone X): Moderate flood hazard area; less regulated but still carries risk.
Construction Requirements in Flood Zones
Buildings in the SFHA (Zone A or AE) must generally: have the lowest floor (including basement) elevated to or above the BFE (plus freeboard required by local ordinance); use flood-resistant materials below the BFE; have openings (vents) in enclosed areas below the BFE to equalize hydrostatic pressure; and for critical facilities, be elevated even higher than the BFE. Basements in the SFHA are strongly discouraged and in some cases prohibited.
Elevation Certificate
An Elevation Certificate documents the elevation of a building's lowest floor relative to the BFE. It is prepared by a licensed land surveyor and is required for flood insurance purposes and for building permit issuance in flood zones. The architect coordinates with the civil engineer and surveyor to ensure the finished floor elevation meets or exceeds BFE requirements, and the Elevation Certificate documents compliance.
Impact on Site Planning
When a project site is in or near the SFHA, the architect must: obtain the applicable FIRM panel(s) for the site, determine the BFE for the site, design the building floor elevation to comply with freeboard requirements above BFE, and consider the impact on parking (surface parking may be allowed below BFE with appropriate drainage), mechanical equipment (should be elevated above BFE), and site grading.
Key Exam Points
- 100-year flood = 1% annual chance flood; defines the SFHA on FEMA FIRMs.
- BFE = base flood elevation; lowest floor must be elevated to or above BFE.
- Floodway: most restricted zone; development generally prohibited.
- Floodway fringe: some development permitted with mitigation.
- Elevation Certificate: required for flood insurance; prepared by licensed surveyor.
Study PA on AREprep
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