When warnings of a major storm or heavy rain are in the news, do you wonder how much your home is at risk of flooding? A critical piece of information for understanding a structure’s flood risk is the first floor elevation (FFE), or the elevation of the lowest finished living space of the house. If you know a building’s FFE, you can determine if the structure is likely to be damaged by the height of predicted flood waters. At a locality or regional level, this information helps decision-makers evaluate mitigation options in terms of cost and loss avoided.
Currently less than 1% of structures in the Hampton Roads region have an official survey recording FFE. FFEs are typically reported through an elevation certificate completed by a licensed surveyor. However, individual structure surveys can be time intensive and costly to collect at a large scale. To help improve our knowledge of residential building FFEs, HRPDC staff has been working with Hampton Roads’ local governments to create a database of existing survey data (now available by searching “Hampton Roads Elevation Certificates” at HRGEO.org). HRPDC staff is then using this data to develop predictions of FFE for structures that lack this information.
A structure’s risk to flooding is dependent not only on where it is located, but also how it is built. For example, a house with a crawlspace foundation will be higher above the ground than a slab-on-grade structure. Using information about a building’s foundation type, the year it was built, and where it is located, HRPDC staff developed a predictive statistical model that estimates residential building FFE. Currently models have only been developed for Hampton and Chesapeake because of data limitations.
For both case study cities, foundation type was the most important component of estimating FFE. However, sufficient detail about building foundation is not always available. Foundation type is also not reported in the same format across the region, which poses a challenge for the current modeling approach. HRPDC staff is beginning to explore alternative estimation approaches and options for improving and expanding the model to other areas of the region.
For more details about the FFE project, check out the full report on the HRPDC’s website. This project was funded, in part, by a Virginia Coastal Zone Management Program (CZM) grant from the National Oceanic and Atmospheric Administration. Funding has been awarded from the Virginia CZM program to continue this work and begin applying FFE estimates in vulnerability assessments to coastal hazards, such as sea level rise, tidal flooding, and storm surge.
Image Source: City of Hampton Property Information Parcel Viewer (2017)