Learn how a building's unique characteristics affect the amount of damage flooding can cause.
Editable building details
A property's Flood Factor is a measure of its likelihood of flooding, not the likelihood of damage to the home. Just because water may reach your home does not necessarily mean water will enter the home and cause damage. For the majority of homes in the US, the elevation of the first floor of living space corresponds to its footprint, but this varies from home to home. Homes with basements may experience more flooding at lower depths, while raised homes may be better protected from higher depths of flooding. Because the damages associated with flooding are greatly affected by property’s specific characteristics, Risk Factor Pro allows you to adjust your home’s property details to see how your home’s unique characteristics, such as building material, number of stories, and square footage directly affect its risk.
Historical data on flood damage costs from the United States Army Corps of Engineers (USACE) is used to identify significant building characteristics.
Flood damages by depth
The damage caused by flooding varies based on depth. Higher depths of floodwater typically causes greater and more costly damage to a home. Even a few inches of water can cause major damage and require costly repairs or replacement of items. Select a depth of flooding from the drop down to see how the property’s likelihood of flooding, estimated repair costs and repair time damage change based on the depth selected.
It's important to note that minor floods are more common than major floods, so lower flood depths have higher likelihoods. Based on the depth of flooding selected the chart tells you the annual probability that depth of flooding reaches the home in a single year.
Estimated repair costs
Estimated cost to repair refers to the estimated cost a property owner can expect to pay as a result of structural damage to their building from a certain depth of flooding over a selected period of time. These cost estimates consider the depth of flooding, property value, number of stories of a structure, the presence of a basement, and the first floor elevation. Using historical records from actual insurance claims, the relationship between depth of flooding and the amount of damage caused is analyzed to estimate a property’s cost to repair flood damage. Estimated repair costs are then calculated by adding each year's annual flood damage estimate over the selected period of time. For example, if a property’s annual flood damage is estimated to be $100 every year, the potential loss to that building would be $1,500 in 15 years.
Estimated repair time
Estimated days for damage repair reflect the total number of days needed to repair the amount of damage caused by a particular flood depth. Estimated repair time is calculated through a process similar to structural damage estimates. However, instead of calculating the cost to repair damaged building materials, repair time estimates evaluate the time needed to repair damaged building materials, as well as factors that delay the start of building repairs. Factors that impede repair start include time for floodwater recession, building restoration, contractor and engineer mobilization, and equipment long lead times. Once the impending delays are resolved, repair time estimates are calculated by averaging repair times for each damaged building component.
Flood damages by likelihood
Flood scenarios describe the recurrence interval of floods. The average number of years between floods of a certain size is the recurrence interval or return period. For example, in any given year there is a 1-in-500 (0.2%) chance that this area will suffer severe flooding. Flood scenarios are used to categorize the likelihood of different severities of flooding. The chart below shows flood recurrence intervals and probabilities of occurrences.
Based on a location’s history and geographic information (such as elevation, climate, proximity to water, and adaptation measures), the First Street Foundation Flood Model calculates multiple annual probabilities, 0.2%, 1%, 10%, 20%, 50%, which consider different depth scenarios. Lower probabilities (0.2%, 1%) represent deeper floods that are less likely to occur, but more likely to reach a building and cause greater damage.
Estimated water to reach first floor
A property’s Flood Factor is based on the likelihood of experiencing flooding and the potential depth of that flood. It considers water depth that reaches the lowest point of the building footprint. 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. Based on the information entered into the Flood-specific property details calculator, the actual amount of water that may enter a home based on its specific ground floor elevation can be calculated.
Say, for example, there is a 1% chance that 3 feet of flood water impacts a given neighborhood this year. One home in that neighborhood has a ground floor elevation of 2 feet, meaning their front door is approximately 2 feet of the ground. Another home has a ground floor elevation equal to its building footprint, meaning their front door is equal with the earth's surface. In this flood scenario, the home with a ground floor elevation of 2 feet will only have 1 foot of water enter and damage their home. Comparatively, the home that is not elevated will have 3 feet of water enter and damage their home.
The depth of floodwater has a big impact on what could be affected in a flood. If 1 foot of water enters a home, electrical outlets, furnaces, and HVAC systems can be damaged. At 3 feet, floodwater can cause damage to the building's infrastructure, water supply, sewage, and plumbing systems; resulting in a much greater cost to the homeowner.
Estimated repair costs
The estimated repair costs are based on the depth of flooding projected to reach a building in a certain flood scenario. Lower probabilities represent deeper floods that are less likely to occur, but more likely to reach a building and cause greater damage. A rare flood event has a only 0.2% chance of occurring in a single year. However if this scenario were to occur, the depth of flooding and amount of damage caused would be much greater than the depth of flooding from very regular events that have a 50% likelihood of occurring.
Estimated repair time
Estimated repair time is the number of days needed to repair damaged building materials, caused by a particular flood scenario. Rarer flood scenarios not only cause greater damage to a home, but the entire area impacted surrounding it, such as time for floodwater recession, building restoration, contractor and engineer mobilization. For this reason repair time estimates consider factors that delay the start of building repairs. Once the impending delays are resolved, downtime estimates are calculated by averaging repair times for each damaged building component.
Annual flood damage estimates capture a homeowner’s expected cost per year to repair flood damage to their home. Historical data from the U.S. Army Corps of Engineers 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.
The increasing cost of flooding
Due to changing environmental factors estimated repair costs generally increase over time as the risk of flooding to a property increases. Changes in the environment have already increased flooding across the United States, particularly in coastal and low-lying areas. As these trends continue into the future, 1.7 million more American properties will be at risk, and the damage and cost of flooding will continue to add up.
If a property’s flood risk is projected to increase in the future, the estimated annual flood damage in 30 years will be higher than the estimated damage this year. However, future annual flood damage estimates do not consider inflation or home improvements that might increase building value, both of which would increase flood damage costs.