Flooding is a significant problem for buildings all around the world, including architectural treasures like the Farnsworth House that have been plagued by the issue time and time again. In particular, one-third of the entire continental U.S. are at risk of flooding this spring, especially the Northern Plains, Upper Midwest, and Deep South. In April of 2019, deadly floods decimated parts of Mozambique, Malawi, Zimbabwe, and Iran as well, resulting in a low estimate of 1,000 deaths while tens of thousands more were displaced. While architecture cannot solve or even fully protect from the most deadly floods, it is possible – and necessary – to take several protective measures that could mitigate damage and consequently save lives.
The first step to take to this end is to identify whether the home or building being designed is in an area at risk for flooding. This can be done by checking flood maps widely available online, including this site run by the U.S. Federal Emergency Management Agency. If it is, the architect and client can decide if they want to relocate or if they would like to stay and take the necessary protective measures. For those who choose the latter, we have delineated nine such measures below.
Elevate Above the Flood Level
To start, architects should build the structure above the flood level to minimize damage if a flood does occur. The flood level elevation for specific areas can be found online using programs such as the Estimated Base Flood Elevation Viewer run by FEMA. With this information, architects can discern how high to raise the building and with what method they should do so. One common way of elevating is by building the structure on columns or stilts. In other cases, the solid foundation can simply be raised higher. For more specific information on what to do, architects should assess the climate and flood history of their area and consult information available online such as this manual on coastal construction in particular.
Build with Flood Resistant Material
Flood resistant materials are those which can last in contact with flood waters for at least 72 hours without significant damage. Flood water can be both hydrostatic (standing water) and hydrodynamic (flowing water), and in most cases will result in displaced foundation walls, collapsed structures, floating fuel tanks, scouring, and more. ‘Significant damage’ suggests any damage requiring more work that cleaning or low-cost cosmetic repair, such as painting. To prevent these damages, flood resistant materials must be durable and resistant to excessive humidity. Examples include concrete, glazed brick, closed-cell and foam insulation, steel hardware, pressure-treated and marine-grade plywood, ceramic tile, water-resistant glue, polyester epoxy paint, and more.
Apply Coatings, Sealants, and Waterproof Veneer
There exist two different types of floodproofing: dry and wet. Dry floodproofing prevents the entry of flood waters, whereas wet floodproofing allows flood waters to enter the house. Coatings, sealants, and waterproof veneer belong to the former, as they prevent water from reaching the interior. A waterproof veneer can consist of a layer of brick backed up by a waterproof membrane, sealing the exterior walls against water penetration. In the interior walls, architects should use washable closed-cell foam insulation in areas below the flood level. Similarly, coatings and sealants may be applied to the foundation, walls, windows, and doorways to prevent flood water from entering the house through cracks, as these openings are rarely designed to be watertight or resist flood loads as they are.
Raise or Floodproof HVAC Equipment and Mechanical, Plumbing, and Electrical System Components
Locating service equipment above the flood protection level is generally the best way to protect it. Such equipment includes heating, ventilating, air conditioning, plumbing appliances, plumbing fixtures, duct systems, and electrical equipment including service panels, meters, switches, and outlets. If these components are inundated in floodwater for even a short period of time, they can become severely damaged and will need to be replaced. Electrical equipment in particular can potentially cause fires if short circuited. It is best that these components are raised above the flood level, but if necessary, they may be designed to prevent damage from flooding, whether through waterproof enclosures, barriers, protective coatings, or other techniques to protect vulnerable components. For precise requirements, architects should consult municipal codes.
Anchor Fuel Tanks
Unanchored fuel tanks are easily moved by flood waters, which could drive the tank into walls, damage other property, and cause contamination if the supply line tears free and fills the water with oil. Even buried tanks can be pushed to the surface due to buoyancy. Thus, it is imperative that fuel tanks are anchored, either by attaching them to concrete slabs that are heavy enough to resist flood water forces, or by running straps over them and attaching them to ground anchors.
Install Foundation Vents or a Sump Pump
An example of wet floodproofing is to install foundation vents, which allow flood water to flow through the home rather than pool around it. While this solution may seem like a counterintuitive one due to the damage it could do to the interior of the property, it actually provides an outlet for the flood water and relieves the damaging pressure that flood water puts on the windows and walls. If the interior – usually a subgrade basement – is prepared using flood damage resistant materials, hydrostatic openings, and protected key equipment, the damage can be limited, although post-flood clean-up will be necessary. Similarly, a sump pump is a type of equipment that pumps water out of basements where flooding happens regularly. Sump pumps with battery backup are highly recommended to allow them to continue functioning when the power goes out.
Construct Permanent Barriers
Placing a permanent barrier around the structure in question can prevent flood waters from reaching it. Such barriers should be constructed using a floodwall made of concrete or masonry, or by using a levee made of compacted layers of soil with an impervious core. While this solution may seem like the simplest or most obvious, both floodwalls and levees require extensive maintenance, and levees need a significant amount of land and usable soil materials for construction.
Install Sewer Backflow Valves
Sewer backflow valves prevent flooded sewage systems from backing up into a home. In certain flood-prone areas, this issue is common, and can cause damage that is both difficult to repair and hazardous to occupants’ health. Generally, gate valves are preferred over flap valves because they provide a better seal against flood pressure.
Grade the Lawn Away from the House
One final method that architects can use to mitigate damage from flooding is to grade the lawn away from the house. If the lawn tilts toward the house, rainwater will pool around the home. Conversely, tilting it outward directs rainwater away. To this end, the lawn should use a heavy soil that contains clay content and sand, allowing the surface runoff to empty into a more appropriate place such as a street gutter.
- http://www.fema.gov/library/viewRecord.do? id=1720
- http://www.fema.gov/library/ viewRecord.do?id=1580
Editor's Note: This article was originally published on May 27, 2020.