Elevation of the Entire Structure

House elevation on Union Street, Nantucket

What is elevation?

“This adaptation method involves raising the height of a building by lifting the building from the
existing foundation, constructing a new, higher foundation, and resetting the building on the new
foundation.”

Jenifer Eggleston, Jennifer Parker, and Jennifer Wellock. “Guidelines on Flood Adaptation for Rehabilitating Historic Buildings.” National Park Service, November 2019. https://www.nps.gov/tps/standards/rehabilitation/flood-adaptation-guidelines.pdf.

“When a house is properly elevated, the living area will be above all but the most severe floods (such as the 500-year flood). Several elevation techniques are available.”

“Elevating Your House.” Federal Emergency Management Agency,  June 2014. https://www.fema.gov/media-library-data/1404148604102-f210b5e43aba0fb393443fe7ae9cd953/FEMA_P-312.pdf

Like FEMA says, there are many forms of elevation. However, elevating the entire building is the most common but also the most harmful to the streetscape and neighborhood character. As part of this series, we will eventually discuss all the potential for elevation and its impact on historic locations. But for now, let’s dig into elevating the whole structure.

Process

When deciding how to elevate an entire building, just like with wet floodproofing and dry floodproofing as we have discussed in previous posts, considerations need to be given to the kind of flooding experienced, the structure of the building, and the character of the neighborhood. No one wants to be next to a person who is elevated ten feet while everyone else is elevated five feet. Also, no one wants to put in a closed foundation system when the water velocity could cause potential collapse. These are the kind of things that need to be thoroughly documented and discussed before deciding on elevating an entire building.

FEMA provides a process to follow when looking at elevating through extending the foundation vertically:

As stated previously, using a closed foundation system may not be the best option for elevating the entire structure. FEMA through the National Flood Insurance Program recommends elevating on an open foundation if the building is in a “V” special flood hazard area. This can be determined by the building’s location on the FEMA Flood Insurance Rate Maps. Using Nantucket as an example below is the digital FIRM map. 

FEMA FIRM map for Nantucket Town
FEMA FIRM map for Nantucket Town

This map can help figure out elevation height requirements. The areas in blue are designated special flood hazard areas which are then assigned Base Flood Elevation (BFE). The BFE is calculated by FEMA using historic data and does not take into account projections, climate change, or ice melt. This is why many areas, including Massachusetts and Nantucket, have adopted additional footage, called Freeboard, into their requirements. If a house on Union Street (putting aside the historic designation of Nantucket for this example) were to elevate, the requirement would be from FEMA a minimum of 8 feet, and the Massachusetts State Building Code designates AE zones to add a foot of freeboard, this puts a house on Union elevating to 9 feet in order to be compliant and qualify for lower flood insurance rates. So, what does this mean for historic buildings?

Historic Considerations

The National Park Service document used above also provides direction on what could be acceptable for historic buildings. Elevation disturbs the historic appearance of the building, and can cause more damage than the water if done incorrectly. Luckily FEMA, and using our prior example of Massachusetts and Nantucket, all have built in exceptions and variances into the policies for historic buildings. This means that the height requirements may not apply if it would harm the historic designation of the building or cause substantial change (a project that is more than 50% of the buildings value.) 

There are ways to disguise elevation to lessen the impact such as purposeful landscaping, filling in the entire site, or putting non-functional details (like windows) into the new section to make it blend better. What is allowed to mask the alteration, depends on what is commonly found in the area and deemed acceptable in the design guidelines. 

Obviously, elevating a single-story historic cottage 9 feet is not an acceptable act because it most certainly would interfere with the appearance of the area and building itself. However, elevating it 3 feet would offer slightly more protection and not disrupt the quaint appearance of the building. 

The images below are the recommended and not recommended actions for elevating an entire structure according to the National Park Service, and in alignment with the Secretary of the Interior’s Standards:

 

Conclusion

Elevation can be a long-term solution to flooding depending on the height and circumstances, but for historic buildings, there is an extra layer of considerations that must be taken into account to protect that resource. Federal, state, and local regulations have made those considerations, at least in Massachusetts, that can help the owner in making decisions about elevating their historic resource.

Do research, know the law, and ask questions!

And finally, Lets Take ACKtion!

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