Six Strategies to Increase Building Resilience, Reduce Vulnerability to Extreme Weather
Hurricane Harvey, which first came ashore on Aug. 25 as the most powerful hurricane to hit Texas in 50 years, has displaced more than 1 million people and damaged nearly 200,000 homes in a path of destruction stretching for more than 300 miles. Low-income and vulnerable communities located in the area’s floodplains have been particularly hard hit. The affected region has many subsidized housing complexes and public housing developments within the hurricane’s path and the 100-year floodplain.
Texas Governor Greg Abbott has estimated damage from Hurricane Harvey at $150 billion to $180 billion, calling it more costly than that of Hurricane Katrina, the storm that devastated New Orleans and surrounding areas in 2005, and Sandy, which overwhelmed New York City and the U.S. Northeast in 2012. The Trump administration has asked Congress for an initial $7.85 billion for recovery efforts.
And HUD Secretary Ben Carson, has reaffirmed his agency’s long-term commitment to Houston’s recovery, saying that it is “a mammoth issue and it’s going to be something we’re going to be involved in for many months, and maybe even a few years.”
As the scope of the damage from Hurricane Harvey and the subsequent flooding caused from foot after foot of rain on Houston and its neighbors becomes clearer, the recovery efforts serve as a stark reminder of the increasing frequency of extreme weather events and the resulting damage done to affordable sites that are not designed or prepared to withstand such extreme climate events. This type of damage not only causes a substantial financial burden for site owners but also jeopardizes the safety and comfort of their residents.
In this article, we’ll cover strategies you may consider employing to reduce your building’s vulnerability to extreme weather, in particular water-related disasters. According to FEMA, water-related disasters account for approximately 85 percent of all disaster declarations, and flooding risks are expected to increase over time. These strategies are based on a HUD-funded multifamily resilience manual released by Enterprise Community Partners that draws on lessons from Superstorm Sandy and other extreme weather events. It provides guidance to owners on retrofit strategies that will help make their buildings more resilient against the effects of extreme weather events.
According to statistics from the Multihazard Mitigation Council, each dollar invested in pre-disaster mitigation leads to an average $4 in savings from avoided damages. You may consider some of the following building resilience strategies as part of a planned series of capital improvements or as part of an action plan for future building upgrades when funding allows.
Determining Exposure to Water-Related Hazards
Housing in coastal areas or next to bodies of water is at the greatest risk of flooding, but heavy rainfall can drastically damage buildings in any area. It’s most likely impractical for sites undergoing retrofit projects to elevate buildings or their building systems above the flood elevation.
To help determine your site’s risk of this type of hazard, you may consider how much damage your site has incurred over the past 10 years due to flooding and evaluate your site’s location and elevation based on the most current flood and sea-level rise data.
The U.S. Department of Homeland Security’s Federal Emergency Management Agency’s (FEMA) flood map service center (MSC) can be found at https://msc.fema.gov/portal. It’s the official public source for flood hazard information produced in support of the National Flood Insurance Program (NFIP). You can use the MSC to find your official flood map and take advantage of its tools for better understanding flood risk.
Another resource is the National Oceanic and Atmospheric Administration Sea Level Rise Viewer at https://coast.noaa.gov/slr. This web mapping tool helps visualize community-level impacts from coastal flooding or sea level rise (up to 6 feet above average high tides). Photo simulations of how future flooding might impact local landmarks are also provided, as well as data related to water depth, connectivity, flood frequency, socio-economic vulnerability, wetland loss and migration, and mapping confidence.
Finally, if the tools show further inquiry is needed, you should hire a surveyor to provide you with an elevation certificate and your flood zone determination. The elevation certificate, which is required when purchasing flood insurance, determines where your buildings lie in relation to the Base Flood Elevation (BFE) level. The BFE is measured from the crest of expected wave height. It doesn’t take into account future sea-level rise from climate change. The surveyor may also give you information if your site is located in an area with a combined sewer-storm water system. Areas with these types of systems are at risk for flooding, even if not located within the flood zone.
Strategy #1: Wet Floodproofing
Wet floodproofing allows unoccupied portions of a building to be flooded during a storm. Compared to dry floodproofing, which makes building and site modifications to prevent water from entering, wet floodproofing involves making a series of modifications to a structure to allow an enclosed area below the BFE to flood through use of openings such as vents or breakaway walls, which are designed to break free from the building when subjected to flood forces. Allowing the unoccupied portions of a building to flood reduces internal and external hydrostatic pressure, or pressure that’s exerted by the water, reducing loads on walls and floors and lowering the risk of damage to the structure.
This strategy can greatly reduce damage and recovery time. Older buildings may not be designed to withstand the hydrostatic pressure that occurs with dry floodproofing (blocking water from entering the building). With these buildings, or when dry floodproofing is prohibited by code, it is important to allow water to flow through a building in a controlled way. The space can then be dried after flood water has receded.
With this strategy, you should relocate or protect equipment that cannot be exposed to water. Electrical panels, mechanical equipment, gas and electric meters, and shut-offs should be relocated from flood-prone areas to locations above the design flood elevation (DFE), the BFE-plus safety buffer dictated by local codes. If that’s not possible, they should be protected in place.
A retrofit project will include using water-resistant building materials below the DFE. Building materials installed in floodable spaces should be able to survive water exposure without major damage, promoting mold or mildew, or absorbing contaminants.
Also, with this strategy, wet floodproofed buildings may require extensive cleanup after a flooding event. Building contamination can occur if floodwater carries sewage, chemicals, or other pollutants into the building.
Strategy #2: Dry Floodproofing
Dry floodproofing encompasses techniques for sealing buildings to keep water out. Dry floodproofing may be less disruptive and have less impact on the building because equipment doesn’t need to be relocated above the DFE.
This method requires a design by a qualified engineer and an operations and maintenance plan, and should include sealing cracks or openings on exterior walls or the foundation, covering entry points below the DFE, protecting against seepage inside the building, and protecting mechanical and electrical systems.
Under dry floodproofing methods, impermeable membranes and sealants can be used to seal walls to reduce or prevent the penetration of floodwater through walls. Another dry floodproofing technique is to use flood shields to make a structure watertight below flood elevation. Flood shields are temporary, watertight barriers erected in front of building openings such as doors and windows prior to flood events, constructed of aluminum, stainless steel, or plastic and use neoprene rubber or similar materials to seal the barrier. The shields are then put in place in preparation for potential flooding or after flood warnings are issued. Most flood shields are able to effectively protect buildings from floods of 1 to 2 feet.
It’s important to note that water pressure of floodwaters places enormous stress on the structure of a dry floodproofed building, so this technique isn’t suitable for buildings with wood frames or which share party walls.
Strategy #3: Site Perimeter Floodproofing
Deploying physical barriers may prevent floodwaters from reaching the building and doesn’t require modifications to the building structure. Flood shields and other permanent flood barriers can be expensive to install and aesthetically displeasing.
A wide range of temporary flood barriers are available as alternatives to traditional sandbags for building owners to set up quickly in preparation for a potential flooding event. A selection of the types of temporary flood barriers include and modular barriers. Inflatable flood barriers are set up prior to a potential flood event and use incoming flood waters to inflate automatically and create a barrier to divert water. And modular barriers can be constructed from a wide range of materials and use floodwaters to deploy.
Compared to sandbags, most temporary flood barriers can be reused and easily deconstructed and redeployed for multiple flood events. In selecting a temporary flood barrier, it’s important to consider the amount of setup time and labor needed to prepare the barrier in addition to factors like cost and protection. Some barriers can be set up by a few people in a short period of time while others will require teams of 12 or more workers and several hours to set up.
Strategy #4: Resilient Elevators
If your site has buildings high enough to utilize elevators, you must provide special consideration to them in your building resilience plan. Elevators are often the only way vulnerable residents have to reach higher floors, making them a critical building system.
Flooding to any building can cause extensive damage, but elevators tend to be the most susceptible because the pits of the elevators are usually one of the lowest points in a building, giving rise to floodwaters. Even outside flood zones, elevators can be damaged by plumbing failures, sprinkler system runoff after a fire, and sewer backup. Here are some important items to consider if you have elevators on your site:
- Ensure elevators have a surge protection system;
- Ensure the standby power generation system works. Sizing of elevator motors are an important consideration when determining backup power requirements;
- Inspect vents, windows, and doors in the machine room for leaks. Elevator shafts that extend below the DFE should be designed and built to resist the hydrostatic pressure of floodwater. Appropriate shaft construction materials include reinforced masonry block and reinforced poured concrete;
- Replace corroded doors and add weather stripping around doors that open to the outside in the machine room;
- Check that sump pumps are operating or purchase one to use after the storm; and
- Install a float switch to stop elevators from running to the bottom landing if the pit floods. Install flood alarms in pits. Install controls to keep the elevator cab out of a flooded shaft.
Prior to a flood, bring elevator cabs to an upper floor above the DFE, park them, and shut off power. If one elevator is kept operational on emergency backup power, it should be prevented from descending to a flooded floor.
After a storm or flooding event, make sure no one is trapped in elevators. If they are, call emergency personnel. Also, you should not resume elevator operation until your elevator has had a thorough inspection. Inspect machine room and pit for water and check for water on control panels and in the machine room before restoring power. If water is found, call your elevator service company. If there’s any damage, record as much information about damage as possible. Take photographs of any damage and save damaged components in case insurance companies need evidence. If an elevator has been damaged, ensure that a technician services it before it’s returned to use.
Strategy #5: Backwater Valves
Sewage backflow occurs when storm water backs up into a building basement because of sewer line blockage or storm drain overflow due to flooding. A backwater valve is a relatively inexpensive retrofit that can prevent significant problems from sewer line failure by blocking reverse flow from entering the building through wastewater pipes.
Backwater valves are installed where the wastewater pipe exits the building, so sewage only flows outward. Valves have a hinged flapper that remains open to allow outward flow, but seals tightly if there is backpressure.
Backwater valves are situated above the external sewer line and should be installed in buildings that have sewer connections below the highest manhole cover in the sewer system, especially if the property is within a Special Flood Hazard Area (SFHA). Although sewer blockage can occur any time, it’s most likely to happen during storms when large amounts of water and debris move through the system.
Municipal codes often require the installation of backwater valves in new construction sited in flood zones. Property owners outside flood zones should also consider backwater valves because sewers can back up any time, not just during extreme weather events. Building codes may also prohibit backwater valves. A plumbing professional will be able install a code-compliant system.
Once installed, you need to inspect backwater valves frequently to ensure there’s no debris in the device or cleanout port and the valve functions properly. And cast-iron backwater valves may be damaged in areas with salt water and heavy minerals in the water. Check them regularly for rust and internal corrosion.
Strategy #6: Sump Pumps/Internal Drainage Systems
Even with the use of dry floodproofing techniques, water may enter a building during flooding events and from general basement leakage. Sump pumps discharge water collected in a small pit that extends through the building foundation from the basement out of the building and directly into a sewer. Internal drainage systems can supplement sump pumps by helping to capture wall and floor seepage. Sump pumps are powered by electricity, and backup generation or battery-operated backup may be necessary in the event of power outages during extreme storms. It’s crucial to ensure that the sump pump has a properly sealed lid. Otherwise, moisture and other pollutants such as radon can enter the building’s basement and crawl spaces, leading to potential health problems and mold growth. Maintenance may be necessary to remove sediment and debris from the sump pit to prevent clogging. Sump pumps remove water that accumulates in the low points in a building, typically the basement. They’re an effective and affordable way to reduce costly flood damages.
Sump pumps can handle moderate flooding but not catastrophic flooding such as a coastal storm surge. Power supplies for sump pumps should be rated for submersion, and wiring should extend up from this equipment rather than along the floor. Locate controls for the system need to be above the DFE. And pumps should be connected to an emergency backup generator to maintain power during outages.