Decoding Disaster Resistant Construction: What is a hurricane proof house?
Characterized by heavy rain and extreme wind, hurricanes are violent storms fueled by the energy of tepid (above 80°F) ocean waters. These storms cannot maintain their intense energy for long once out of the water. Unfortunately, hurricanes are often on land long enough to devastate coastal communities.
Although we can't always predict the weather, with new technology in the building and construction industry, homeowners can build stronger and more storm-resistant homes or retrofit existing homes with disaster mitigation in mind.
The quality of every construction component is important, but it's the sum of these parts that keep homeowners safe. A hurricane proof house is a seamless house. Every element (roof, foundation, walls) must be securely attached to the next. A small hole or gap is enough to allow wind to enter a structure during a hurricane. When wind or water enters a home during a storm, enough pressure can be created inside the building to push the walls and roof apart potentially causing structural collapse.
Components of a Hurricane Proof House
Spray Polyurethane Foam & Wind Uplift Protection:
The roof is a home's first line of defense in a hurricane and often the first failure. If a roof fails, the likelihood of complete structural failure is heightened. For new homes and old homes, using closed-cell spray polyurethane foam (SPF) insulation as an adhesive can reduce your energy bills and more than double the wind uplift resistance of your roof (where most hurricane devastation occurs).
Miami Dade County in Florida has a hurricane resistant product certification process to help guide builders and homeowners in the construction process. BASF SPRAYTITE® insulation are the only closed-cell spray foams that are currently approved for use in the "High Velocity Hurricane Zone (HVHZ)" from the Miami Dade County Building and Neighborhood Compliance Office and provide nearly two times more resistance to wind uplift than standard code-built homes. This is due to their rigid closed-cell composition, which adds structural integrity to roofs (and walls) and adheres directly to all surfaces, creating a chemical bond between the roof and the vertical walls.
Closed-cell SPF is also a proven solution as an air, vapor and wind uplift barrier on flat roofs. In June 2006, the National Institute of Standards and Technology (NIST) released Performance of Physical Structures in Hurricane Katrina and Hurricane Rita: A Reconnaissance Report a documentation of damage to major buildings, infrastructure, and residential structures resulting from wind and wind-borne debris, storm surge, surge-borne debris and surge-induced flooding. SPF roofs scored well above the average when it came to weathering Katrina and Rita.
The NIST report states:
"A number of spray polyurethane foam (SPF) roofing systems were observed ... Some of these roofs were estimated to be about 20 years old. With one minor exception, all were found to have sustained Hurricane Katrina extremely well without blow-off of the SPF or damage to flashings."
Hurricane Straps and Anchor Bolts:
An additional tool to reduce wind uplift, hurricane straps made of galvanized steel exist to help keep a roof attached to the frame of a building during a hurricane. They are also used to strengthen the connection between multiple floors.
A similar safety measure, anchor bolts secure a home's walls to the foundation.
Impact Resistant Windows:
Often the most vulnerable part of a home in high winds, windows can easily shatter, allowing strong winds to enter a home, creating pressure and greatly compromising structural integrity. Impact resistant windows can help eliminate this danger and can act as a home's defense against structural failure in a hurricane. Impact resistant windows are comprised of several layers of laminate material sealed by heat between two panels of glass.
To meet building codes, high resistant windows must undergo extensive testing. This testing involves firing a 9 pound 2x4 wood missile at both the center and corner of a window unit at 50 feet per second (in Florida, windows must remain intact after being hit with missiles traveling at a speed of 80 feet per second). The window is expected to crack but must not shatter or leave the frame to be deemed "impact resistant."
To be certified as an impact resistant window, the unit must also pass inspection after exposure to simulated 200 mile per hour winds.
A common fixture on homes in hurricane prone regions like Florida, hurricane shutters cover both windows and doors during a high wind storms. Shutters can be permanently affixed to a home or can be stowed away until storm warnings begin.
Although permanently installed hardwood or metal shutters (either aluminum or steel) are a homeowner's most dependable option during a hurricane, plywood can also be used as a less expensive option to provide minimum protection to exposed windows.
The Federal Emergency Management Agency(FEMA) encourages homeowners to install permanent hurricane shutters if you live in an area where hurricanes are common and you may not have ample time to prepare your windows before a storm starts.
The same care should be taken to protect garage doors as any other entrance or window. This is critical for homeowner's with attached garages. An attached garage is a part of the framework of a building. If wind enters through a flimsy garage door, the entire structure is vulnerable to severe damage. Supports can easily be attached to existing garage doors at a low cost to the homeowner. The Federal Alliance for Safe Homes (FLASH) estimates an average garage door retrofit can be achieved for around $300. FLASH also recommends that the retrofit be done by a professional to maintain the appropriate balance of the door system.
When it comes to building or retrofitting a hurricane proof house, knowledge is power. That is why organizations like the Federal Alliance for Safe Homes (FLASH) and the Federal Emergency Management Agency (FEMA) exist to educate homeowners in disaster preparedness and hurricane damage mitigation.