Risk Score Methodology

Factor 1 — Official Flood Zone Classification

Floodfolio incorporates FEMA's official flood zone designation for the property, sourced from FEMA's national flood mapping program. FEMA flood zones reflect hydrologic and hydraulic studies of flood hazard and are the federal government's primary mechanism for communicating flood risk.

Higher-hazard zones carry higher base scores. Special Flood Hazard Areas (SFHAs) — including AE, VE, AO, and AH designations — are scored at the high end of the range. Minimal-hazard zones are scored at the low end.

Floodfolio differentiates between the shaded and unshaded variants of Zone X — a distinction that many consumer-facing flood maps do not make but that is meaningful in the Houston metro, where the 500-year floodplain experienced significant losses during Hurricane Harvey.

Factor 2 — Elevation Analysis

For properties inside a Special Flood Hazard Area, Floodfolio computes the difference between the property's estimated ground elevation and the FEMA-assigned Base Flood Elevation (BFE) — commonly called freeboard. Properties below the BFE receive higher scores; properties with meaningful elevation above the BFE receive lower scores. The direction and magnitude of this gap is the most property-specific factor in the score.

For properties outside the SFHA, Floodfolio evaluates the property's ground elevation in the context of the nearest flood benchmarks in the surrounding area. A Zone X property sitting only marginally above the nearest SFHA boundary carries meaningfully different exposure than one with substantial elevation separation — and the score reflects that distinction.

Ground elevation is estimated from high-resolution LIDAR data sourced from the USGS 3D Elevation Program (typical vertical accuracy ±1–2 ft RMSE). Elevation-based adjustments are not applied when elevation or benchmark data is unavailable for a location.

Factor 3 — Hurricane Harvey Flood History

Hurricane Harvey (August 2017) was a record rainfall event that inundated properties across all FEMA zone designations in the Houston metro — including tens of thousands of Zone X properties that carried no mandatory flood insurance requirement. The storm's actual footprint differs substantially from FEMA zone maps in many areas.

Where storm inundation data is available for a property, it directly informs the score in proportion to the depth recorded. Where property-level data is unavailable, neighborhood-level insurance claim patterns serve as a proxy signal for whether the surrounding area experienced Harvey flooding.

Factor 4 — Historical NFIP Flood Insurance Activity

Federal flood insurance data provides a real-world record of flood frequency that complements — and sometimes contradicts — the FEMA zone map. Floodfolio incorporates two complementary signals from this source:

Multi-storm claim history. Floodfolio counts the distinct named storm events across 14 Houston-area storms (1979–2024) that produced meaningful insurance claims in a property's ZIP code. A neighborhood that flooded in multiple separate events has a documented pattern of exposure that no single storm can fully capture.

Repetitive Loss property density. The federal NFIP program maintains records of Repetitive Loss (RL) and Severe Repetitive Loss (SRL) properties — addresses that have filed multiple flood insurance claims over time. A high concentration of these properties in a ZIP code is an independent signal of persistent, neighborhood-wide drainage or topographic flood vulnerability.

For properties outside Special Flood Hazard Areas, Floodfolio applies additional analysis to both signals, accounting for the possibility that ZIP-level claim activity may be concentrated in lower-elevation parcels elsewhere in the area rather than at the specific property being assessed.

Score Output

The factors above are combined using Floodfolio's proprietary weighting model and expressed as a whole number from 1 to 10. A score of 1 reflects the lowest assessed flood risk given available data; a score of 10 reflects the highest. Not every factor will have data for every address — the score is calculated from the factors that are available, and the report identifies which factors contributed and in what direction. The specific weights and thresholds used in Floodfolio's scoring model are proprietary and are not disclosed.

Known Limitations

• The score is Floodfolio's proprietary analytical output. It is not an official government rating and has not been reviewed or endorsed by FEMA, USGS, or any government agency.
• The score reflects government data as of the query date. FEMA map amendments, new NFIP claim releases, and updated elevation surveys may not be reflected immediately.
• Elevation estimates carry inherent uncertainty (±1–2 ft typical), which can affect scoring for properties with freeboard near zero.
• Property-level storm inundation data is not available for all addresses; the score falls back to neighborhood-level NFIP claim signals where property-level data is absent.
• NFIP claims data is presented at ZIP code level and reflects aggregate neighborhood activity, not individual property claim history.
• The score does not account for local drainage infrastructure, subsidence, building first-floor elevation above grade, or other property-specific conditions not captured in public datasets.
• LIDAR elevation coverage is approximately 87% of the 5-county service area. Properties outside coverage receive a score based on available factors only.