Decoding Disaster Resistant Construction: High Performance Materials in Safe Room Construction
We count on our homes to shelter us from the elements and keep us safe. Unfortunately, as we’ve seen from the destruction caused by the tornadoes in Alabama and Missouri, sometimes our homes are no match for Mother Nature. Fortunately, when houses fail, safe rooms exist to provide homeowners and their families with protection against the most powerful tornadoes and hurricanes.
The right place at the right time
Because tornadoes can strike with little to no warning, safe rooms are most effective when they are readily accessible. A safe room can take several forms. Functioning rooms on the ground floor of a home such as a bathroom or closet can be reinforced to double as a shelter in severe weather as long as the walls, ceiling and foundation of the room are structurally independent of the rest of the home. Basements or garages can also be retrofitted to meet federally regulated storm shelter guidelines.
Safe rooms can also exist outside of the home, but the Federal Emergency Management Agency (FEMA) recommends an “in-residence safety room” in a basement, in a centrally located room on the first floor of a home or on a “concrete slab-on-grade foundation or garage floor”. Homeowners with in-residence safe rooms don’t have to go outside during severe weather and risk exposure to high winds and flying debris. FEMA also notes that homeowners living in flood zones should not build safe rooms for hurricane protection or for tornado protection where heavy rainfall may cause flooding.
Safe rooms add value to your home
Although storm shelters can be installed in a pre-existing home, they are significantly less expensive when included in the initial blueprint. According to the Federal Alliance for Safe Homes, when installed during the construction of a house, a homeowner can expect to spend between six and eight thousand dollars. When an existing home is retrofitted for a safe room, the cost is generally closer to ten thousand.* Although the cost can be significant, adding a safe room increases a home’s value and in some regions can qualify a homeowner for tax breaks. Federal grants also exist to assist homeowners with construction costs.
Choosing the right materials
In 2003, researchers at Texas Tech University’s Wind Science & Engineering Research Center conducted a series of trials during which a variety of wall assemblies were tested for hurricane and tornado resistance. Researchers simulated 250 mile per hour winds and the impact of storm debris on a home by firing a 15 pound 2×4 wood missile at 100 miles per hour at several different wall panels to see which materials could absorb the impact without being perforated. The results of these trials were used to create the publication, FEMA 320: Taking Shelter from the Storm, a homeowner’s guide to safe room building materials and procedures.
Traditional safe room materials
Walls built with concrete masonry units and reinforced with rebar are a classic solution for safe room construction. Economical and durable, one trial at Texas Tech tested the resiliency of this wall by firing missiles at the same assembly over thirty times.
Wood-framed safe rooms reinforced with metal sheathing provide homeowners with a way to add protection to an existing home with a concrete slab foundation. According to the Wind Science & Engineering Research Center at Texas Tech, plywood and heavy-gauge sheet metal can be added to a room’s existing walls and securely anchored to the foundation to create a durable storm shelter.
Insulated concrete forms (ICFs) were among those materials tested by Texas Tech University. ICFs are created by pouring concrete into a mold made of foam insulation. When the ICF wall assembly was tested, the concrete was completely unharmed by the flying debris. Used to construct safe homes in addition to safe rooms, ICFs also provide stellar insulating performance. According to the Insulating Concrete Form Association, houses built with ICFs require 44% less energy to heat and 32% less energy to cool than traditional frame homes.
Another emerging technology in tornado and hurricane resistant building design are structural insulated panels (SIPs). SIPs are produced by sandwiching rigid foam insulation between two sheets of oriented strand board (OSB) or metal substrate. Some have been specially engineered to meet the wind and debris impact guidelines set by FEMA 320. This means that safe rooms built with SIPs are strong enough to withstand 250 mph winds and the impact from resulting debris. Because they come in pre-fabricated panels, SIPs can increase construction efficiency and reduce cost when compared to traditional materials.
Doors and hardware
A storm shelter is only as safe as the sum of its parts. When building a safe room all building materials must be carefully selected and installed. This includes doors and hardware. During a tornado, an open door or window makes a structure significantly less sound. In addition to the walls, ceiling and foundation of a safe room, the door must also be able to weather the same impact to keep occupants safe. “FEMA does not certify specific products for use, but any manufacturer can have their products tested to demonstrate that the FEMA criteria have been met.