The level-up strategy: Responding to sea level rise in coastal communities
April 02, 2020
April 02, 2020
To adapt to the growing threat of floods, low-lying communities must change the way they build
People have been building next to bodies of water for centuries, whether out of economic necessity or simple desire. While building in these low-lying areas has always carried a heightened flood risk, that risk has increased and continues to grow exponentially due to climate change and sea level rise. Each year, hurricanes and tropical storms wreak havoc on coastal communities with increasing frequency and intensity. These events take serious financial and social tolls on their citizens, businesses, and governments.
After a storm, private rebuilding costs are split among the National Flood Insurance Program (NFIP), Federal Emergency Management Agency (FEMA) grants, and private funding. As flood and storm surge events have become more prevalent, the current model for repairing and rebuilding is no longer financially sustainable. According to the U.S. Government Accountability Office, FEMA’s debt alone reached $20.5 billion in September 2018 even after Congress canceled its $16 billion debt the previous year. As of December 2019, the NFIP owes $20.525 billion to the U.S. Treasury.
The desire to build by and live in coastal areas that have a high flood risk may never change, but over time it will become more expensive for both private owners and public agencies. It is imperative that we build and adapt in a way that allows affected areas to recover quickly and affordably, while maintaining the beneficial connections to street-level activity and community engagement.
Building on the coast or in flood-prone areas requires adherence to FEMA guidelines, which are designed to reduce flood damage and costs. The agency determines the base flood elevation (BFE) on each site, which defines where a building’s ground floor must be built to qualify for a building permit and the National Flood Insurance Program.
When building on low-lying sites, developers turn to flood proofing strategies—the most common of which is dry flood proofing. In a dry flood proofed building, all elements of the structure are protected from rising water by hydrostatic slabs and walls, while flood panels are utilized at all entrances prior to flood events. This strategy has two major drawbacks.
My home—Miami—and others must adopt a strategy that allows for flooding to occur while reducing the costs of rebuilding.
First, the cost of hydrostatic construction and flood panels is often substantially higher than wet flood proofing—allowing water into the building. Second, and more importantly, there is no guarantee that it will work.
FEMA post-storm evaluations document significant failures of dry flood proofing systems. These systems are only as effective as their weakest link, and there is a serious potential for failure, especially when storm surge is higher than the BFE of the site. All it takes is one weak link in the system to negate all the work that went into preparing for a flood. As growing coastal communities face a future of increased flooding and storm events, my home—Miami—and others must adopt a strategy that allows for flooding to occur while reducing the costs of rebuilding.
Several years ago, while working on a project in St. Thomas, a hurricane struck the island. I flew in after the storm to discuss a rebuilding strategy for my project. While I was there, I noticed that all the electrical poles had been blown over. I found it strange that the poles had been installed only a few feet into the ground—not enough to withstand the hurricane winds. The reason, I learned, came down to cost and efficiency. Burying the polls deeper would only increase the risk of them breaking in a storm, and it would cost more to ship a new pole to the island than to simply reinstall those blown over. Therefore, installing the poles and cables in a way that would minimize the damage and cost of recovery was just common sense. We can apply a similar strategy to buildings.
We call this the “level-up strategy,” and the concept is simple: move all critical building systems above the damaging flood waters to the second floor, while converting the ground level into floodable exterior space. Also known as wet flood proofing, it’s perhaps the most cost-effective and efficient way to deal with sea level rise. In a wet flood proofed building, the ground floor is built in a way that will minimize the cost of refitting the space after a storm. This includes the of use concrete, stone, and other materials that can handle flood conditions. Additionally, minimizing the amount of enclosed air-conditioned space at ground level can greatly reduce the time and cost of recovery.
By accepting that flooding is inevitable and adapting accordingly, the level-up strategy will also minimize the cost and time associated with getting buildings and businesses up and running after a serious storm. Major building systems, such as electrical switch gear and fire alarm panels, damaged by flood waters take up to a year to source and replace. By protecting critical elements from damage, the work to reopen the building is limited to drying a structure and replacing limited ground-level elements that were damaged by water. The level-up approach would minimize insurance costs for storm reconstruction and mitigate the economic impact from loss of business.
With critical building services relocated to the second level, the ground plane again becomes available for public or private use. Rather than meeting the street with an rated walls concealing sensitive equipment, the building can engage its context with open public spaces. The dual benefit of the level-up strategy is that is can improve building recovery times during a flood event and improve the urban condition around the building in fair weather. In coastal communities like Miami Beach, this strategy could connect the beach to the urban context.
Despite the benefits, adopting a level-up strategy comes with several challenges—the largest are the need for regulatory changes and economic incentives to encourage property owners and developers to embrace this approach.
For owners, the ground level of a building has significant economic value. A transfer of development rights and other incentives will be needed to mitigate the loss of revenue-generating area at the ground floor. If an owner will give up floor area (FAR) to build exterior spaces under their building, they should be allowed to transfer that unused FAR elsewhere in the building. They can still generate income from the exterior ground-level uses such as bars and restaurants, pool decks, reception areas, and parking—all which work well as exterior spaces and can be serviced by utilities and kitchens on level two.
Fire departments will also need to allow the fire command rooms to be located at level two. A dedicated stairway extending to the ground level provides priority access. Similarly, utility providers will need to allow their transformer to be at level two. Some are already doing this on certain projects and for years have allowed stacked transformer vaults in high-rise buildings. Access to this equipment will need to be provided, which will require cooperation from power-regulation agencies as well as state and local building and fire officials.
In many ways the level-up strategy is a return to our roots of coastal construction. Raised houses that were built decades ago still stand along our coastlines and serve as examples that wet flood proofing is a viable and sustainable option for flood-prone areas. Perhaps the greatest opportunity in this strategy is the possibility to producing better resident and tourist experiences that enhance the street-level fabric of our cities while creating more resilience.