How are flood damage estimates and Flood Factor scores related?

Learn about the relationship between a property’s Flood Factor and  annual flood damage estimates. 

A home’s Flood Factor is associated with its risk of flooding and is not based on flood damage estimates. 

A Flood Factor tells you the likelihood of flood water reaching the building structure at least once over the next 30 years. It’s important to note that water reaching the structure doesn't necessarily equate to water entering the home. How quickly the water reaches the building, how long it stays, and the home’s foundation type have a lot to do with the actual damage the home may experience. 

For example, homes with basements may experience more costly flooding at lower depths while raised homes may be better protected from higher depths of flooding. The estimated damage costs provided by Flood Factor take these, as well as other building characteristics into consideration. 

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How is my Flood Factor calculated?

That data on Flood Factor comes from the First Street Foundation Flood Model, a nationwide flood model that calculates the likelihood of a flood based on a location’s history and geographic information, such as elevation, climate, changes in the environment, proximity to water, and adaptation measures.

A property’s Flood Factor is determined by its likelihood of flooding and the potential depth of that flood. Because flood risks accumulate over time, it specifically looks at the likelihood of 1 inch of water reaching the footprint of the largest home or building on a property at least once within the next 30 years. The First Street Foundation Flood Model is used to determine the likelihood of a flood occurring within a given year and the projected depth of a flood.

What are annual flood damage estimates and how are they calculated?

Flood damage  estimates refer to the costs of potential flood damage.These cost estimates consider a number of factors such as projected flood risk, property value, and building characteristics and are calculated either for the annual risk from all flood events, the cumulative expected loss over a period of ownership, or from the expected loss from a specific event probability

  • The First Street Foundation Flood Model is used to determine the projected depth, likelihood and type of flooding the building is at risk for. 
  • The approximate property value, including both the value of the physical building structure as well as the value of the land the property sits on. This data is provided by ComeHome by HouseCanary’s automated valuation model (AVM). Where AVMs are not available from ComeHome, they are estimated using the building characteristics through a peer-reviewed methodology developed by First Street Foundation.  
  • Building characteristics such as the number of stories of a structure, the presence of a basement, and the first floor elevation. This data comes from the National Structures Inventory (NSI) database or Lightbox, a leading provider of commercial real estate data.

These factors are then used together and applied to historical data on flood damage costs from the United States Army Corps of Engineers (USACE). The USACE data analyzes the relationship between depth of flooding and the amount of damage caused, based on historical records from FEMA insurance claims. This then provides an estimate for expected loss per year that a property owner can expect to pay as a result of damage to their home from flooding. Because the risk of loss changes as environmental conditions change, damage estimates generally increase over time as the risk of flooding to a property increases. It’s important to note that these estimates only consider damage costs to the structure of the home and do not include costs to replace damaged contents, and do not consider inflation. 

Are flood damage estimates based on my Flood Factor? 

A home’s Flood Factor is not based on its flood damage estimates. However, because both Flood Factors and flood damage estimates are based on flood risk projections, there may be some correlation. 

While homes with high flood risks are likely to have higher annual flood damage estimates, it is still possible for a home to have a low Flood Factor and high damage estimates, or a home to have a high Flood Factor and low damage estimate. The distinction is that Flood Factors capture risk of flooding, while flood damage estimates the physical impact of that flooding.

For example, a property with a high Flood Factor that is projected to receive 3 feet of flooding may have low annual flood damage estimates if the home is raised higher than 3 feet. While there is still a possibility the home could be damaged, the model would project that flood water would not reach the first floor. 

Homes with similar Flood Factors but at risk from different flood types may also show a difference in damage estimates. For example, a home at risk of flooding from heavy rains may have lower damage costs compared to a home at risk of flooding from a river overflowing, as river flood water typically takes longer to subside and can cause more damage to a structure as a result.

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Home that has been elevated by extending the home’s foundation.

 

Learn more

About Flood Factor scores

Understanding your home’s estimated flood damage costs

Where does the information used to calculate flood damage estimates come from?

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