Blowing Up the House

Shifting Sands

Eye on the Sky


Blowing Up the House

When the big one blows through, it'll be the windows and doors that keep the house upright Imagine a house on the beach facing sustained winds of more than 75 mph and periodic gusts reaching above 120 mph. As long as the house remains intact, these hurricane-strength winds will blast the ocean side of the house with pressures measuring over 40 psf. As the winds rise over the rooftop and rush around corners, suction pressures in the wake of the blast will exert even greater pressures on the sides and back of the house. These pressures will reach their peak — as high as 75 psf of suction — at the building's corners, eaves, and ridges, where the wind causes wild fluctuations in pressure that push and tug erratically at cladding and roof coverings.

That's if the house stays intact. Now imagine these winds ripping out the neighbor's fence and hurling it through a window or patio door. "Once you breach the envelope, the air rushing in pressurizes the building just like blowing up a balloon," explains Scott Schiff, a civil engineering professor and director of Clemson University's Wind Load Test Facility. Now you have positive pressure pushing from inside and negative pressure pulling from outside. In the best case, these pressures will blow out all the other windows in the house, equalizing the pressure before severe structural damage can occur. More disastrous (and likely if the house was poorly framed), the entire trussed roof assembly or whole wall sections blow out. "The house literally explodes," says Schiff. "If it doesn't actually come apart, it's drenched by all the wet air racing through the interior."


During Hurricane Andrew, which meted out gusts up to 165 mph, scenarios like this were common enough that damages mounted to over $15 billion in insured losses. This made Andrew the costliest natural disaster in insurance history, according to the Insurance Information Institute. The hurricane destroyed 28,066 homes and damaged 107,380 others. While many of the destroyed homes included house trailers that blew over for lack of foundations, many permanent homes were torn apart by wind-borne debris, and a majority of the damage was related to openings that allowed wind-driven rain to soak interiors. "The insurance pressure after Andrew, and to a lesser extent Hugo which preceded it, has been tremendous. It's brought a new emphasis on property damage in the building codes, not just on human safety and loss of life," remarks Schiff.

In Andrew's wake, a majority of this attention has focused on protecting house openings, including windows, entry doors, sliding glass doors, garage doors, gable-end vents, and skylights. Miami-Dade and Broward Counties were the first to act, issuing impact-resistant safeguards as part of a revamped 1994 South Florida Building Code that also beefed up the requirements for sheathing, nailing, rafter ties, and sill-plate connections to help resist internal pressurization. At the time, the impact-resistant measures amounted to requiring hurricane shutters for all window and door openings and reinforcement for garage doors. "Suddenly everyone's selling 'hurricane shutters,' but there was no standard for what type of shutter would effectively resist the impacts," added Schiff.

Winds whipped up by Hurricane Isabel came rushing in the ocean-side windows and doors of this North Carolina home, pressurizing the interior until the entire back wall blew off. (Photo by Vince Lupo).


It took another three years to develop a test standard for evaluating windows and doors, as well. "The idea was to develop an impact test that would simulate the effects of wind-borne debris on any building product," explained David Hattis, chairman of the committee of the American Standards for Testing and Materials (ASTM) that is responsible for the development of this new standard. Initiated by the Southern Building Code Congress International, the development of the test was soon handed over to ASTM when it became contentious. "The measure was supported by academics and code officials, but opposed by window manufacturers and homebuilders," Hattis said. "The ASTM process is designed to achieve consensus."

The resulting test procedure, ASTM E1886, has two parts — a large missile test that shoots a 2x4 from a compressed-air cannon at a velocity of 50 feet per second (34 mph), and a small missile test that uses ball bearings traveling at 80 feet per second (50 mph). After each impact, the product, which is installed on a test wall or roof assembly, must undergo 9,000 pressure cycles to simulate the damaging pressure fluctuations of turbulent winds. These tests work in concert with a companion standard, E1996, which designates the wind zones where test-compliant products are required and establishes pass/fail criteria for the tests. To pass after impact and pressure cycling, the assembly cannot have a hole large enough to fit a 3-inch sphere, or a tear longer than 5 inches.

Under E1996, which was adopted into the 2000 International Residential Code (IRC), "windborne debris" regions are defined as follows: Hurricane-prone regions within one mile of the coastal mean high-water line where the basic wind speed is 110 mph or greater; or anywhere the basic wind speed is 120 mph or greater. By code, builders working within these zones are required to install storm shutters or laminated-glass windows and reinforced side-hinge doors and garage doors that can pass the missile-impact and pressure-cycle tests. In states that only recently adopted the IRC, the trick has been finding suitable products. A couple years ago, only some aluminum windows held an appropriate Miami-Dade County Notice of Acceptance — the only certification available then — but these single-pane units were not acceptable in cooler climate regions where clients demand the comforts of insulated glass. By this year, however, most of the top window manufacturers have introduced a wide range of insulated and non-insulated impact-resistant products, and manufacturers in other product categories are catching up, though not without difficulty.

"Initially, many coastal counties were shocked by the rules for openings when the IRC was first adopted," said Dean Lewis, certification manager for the American Architectural Manufacturers Association (AAMA). "Many issued a moratorium until there were products available that could meet the standards." In March 2004, AAMA completed a certification program for side-hinged entry doors that gives door manufacturers a third-party certification of compliance with the ASTM standards. According to Lewis, contractors and code officials had little assurance prior to this program that manufacturers were actually meeting the standards.


As recounted by Hattis, the ASTM impact standards have gone through numerous revisions in a few short years and are likely to undergo more. The first revision came after skylight manufacturers argued that roof windows are not as likely to be struck by heavy objects as windows lower on the building, and that skylights make up a much smaller percentage of the vulnerable surface area. The result was a new table in the standard that lists lower impact requirements for skylights. A second revision came from the effort to fold the Miami-Dade county requirements into the ASTM standard. There has been considerable discussion over whether the entire coastline should be subject to the extreme conditions faced in Miami-Dade County, says Hattis. A solution was found by adding a new zone subject to winds in excess of 140 mph. The new wind zone applies to Miami-Dade and Broward Counties, parts of the Florida Keys, some sections of the Louisiana Delta, and the southernmost tip of Texas. Shutter manufacturers brought forward a third revision that sought clarification on how many product specimens had to be tested. Shutters may come in hundreds of different models, even though the basic construction of models is similar.

The standard also has withstood numerous challenges by the National Association of Home Builders (NAHB), which remains the principal opponent to the measure. As an example, a 2001 report by the NAHB Research Center argued that hurricane-force winds at lower speeds are unlikely to launch 2x4-like projectiles, and that in residential areas where gravel is seldom used as roof ballast, ball bearings are not good representations of actual windborne debris. ASTM's Hattis counters that although it is true houses are more likely to be pelted by asphalt shingles than 2x4s, any standardized test must be repeatable. The test missile must be accurately aimed to hit the test assembly in precise locations, such as at the intersection of mullions or near the latch. Attempts to create accurate missiles with asphalt shingles failed, reports Hattis. Eventually the standards committee agreed to shorten the 2x4 to simulate a lighter missile. "Reaching consensus on these standards is always a political and commercial compromise," Hattis concluded. He also conceded that, going forward, it's possible that the standards will evolve to include two different criteria: one for windborne debris regions subject to lower-speed winds, and one for higher. — Clayton DeKorne

Shifting Sands

Engineered beaches redefine U.S. coastlines Most U.S. beachgoers have never heard of the Ash Wednesday storm, which pounded the New Jersey coast in the spring of 1962. But they can thank it for the sand beneath their feet. The storm so eroded Jersey's booming beaches that the U.S. Army Corps of Engineers initiated the feds' first big foray into what has become a billion-dollar effort to continually replenish beaches along U.S. coastlines.

Brevard County, Fla., with assistance from the Army Corps of Engineers, renourished beaches in 2003 using sand leased by the Department of the Interior's Minerals Management Service. (Photo courtesy Marine Minerals Program, Minerals Management Service)


Shaped by tides, currents, and storms, beaches erode, build up, and shift. Over centuries, their nemesis is rising seas, says Bob Dean, a recently retired University of Florida coastal engineering professor. In the shorter term, the prevailing northeastern winds angle waves and sand southward along the entire East Coast. The process depletes some beaches and builds up others, while inlets impede the flow. For example, Dean blames the 19 Atlantic-side inlets in Florida — 16 of them manmade or altered — for 80 to 85 percent of erosion on the state's coastline. Structures such as jetties, initially thought to stabilize beaches, had the opposite effect and now are banned in some states.

As erosion worsened, the Corps' replenishment program intensified. This year's 51 projects include 15 in most-replenished Florida and 9 in runner-up New Jersey — where virtually the entire coast is slated for renourishment. Most projects occur along the heavily developed New York to Miami shoreline, but the Corps also pumps sand onto Gulf Coast, West Coast, and Great Lakes beaches. The annual federal tab: over $100 million. State and local residents kick in millions more through a cost-share arrangement established in 1988, in which they provide 35 percent of the financing for projects; the other 65 percent comes from federal money.

An offshore hopper dredge pumps excavated sand ashore where bulldozers distribute the slurry for Brevard County's Shore Protection Project.(Photos courtesy Marine Minerals Program, Minerals Management Service)


The payoff for renourishment depends on your point of view. Beaches absorb wave impacts. The wider the beach, the more likely storm-driven waves will exhaust their energy. The Corps, which agrees to renourish a beach only if reduction of potential storm damage exceeds half the cost, says its main goal is to protect communities. That's also the chief lightning rod for critics, who say the consequence is that people build where they shouldn't. "These areas are inherently risky," says Kate Costenbader, a Corps-reform advocate with the National Wildlife Federation.

Beach renourishment affords other advantages. "Nourishment stimulates the hell out of development," observes Steve Benton, coastal hazards coordinator for the N.C. Division of Coastal Management. It also means more valuable real estate, which prompts landowners and developers to build more expensive structures, says Professor Dean, a renourishment supporter.

Nevertheless, the growth-spurring mechanism is indirect. To qualify for federal aid, beaches must already be developed. In most states, renourishments aren't allowed to change construction setbacks. Washington and South Carolina are the exceptions, and South Carolina's policy has drawn only one application, says Richard Chinnis, director of regulatory programs at the S.C. Office of Ocean and Coastal Resource Management. The more common avenue for setback relocations, says Chinnis, continues to be the state's once-a-decade review of coastal jurisdictional lines.


With typical renourishments lasting only 3 to 10 years, many Corps projects are planned as 50-year efforts with multiple return visits. No one claims renourishment is a permanent solution. For this reason, critics say it's a waste of taxpayer dollars that is made even less palatable by environmental threats, ranging from the destruction of sea turtle nesting to the muddying of fish habitat. "These are projects that are intended to fail," Costenbader says. Supporters counter that renourishments pump up tourism, property values, and local and state economies, resulting in a net gain. Both the Clinton and Bush administrations have rejected that argument, seeking to reduce the federal contribution. Bush's proposed 2005 budget would slash this year's fund of $106 million to $57 million, eliminating more than 40 pending projects.

But supporters aren't worried. Lobbied intensely by the American Shore & Beach Preservation Association (ASBPA) and others, Congress has repeatedly exceeded presidential requests. The 2004 budget, for example, is $21 million more than Bush proposed. Says Harry Simmons, ASBPA president, "[Legislators] in both parties and both houses are overwhelmingly in support of putting it back in the budget." — Aaron Hoover

Eye on the Sky

NOAA knows weather, so you can, too The night before scheduling a lumber delivery or opening up a roof to tie in an addition, Mike Smith remembers how his father sat hunched over a small transistor weather radio, trying to decipher the staticky signals. "Most of the time, we were listening to nautical reports miles offshore. It was impossible to tell what would actually blow ashore or when," remembers Smith, a second-generation Miami-based remodeler. "It wasn't today's weather service, that's for sure."

These days, Smith and other coastal contractors rely on the many online weather-warning tools produced by the National Oceanic and Atmospheric Administration (NOAA). "It's amazing how much you can gather about the weather online," avows Smith. Smith begins by monitoring the local pages of NOAA's National Weather Service Forecast Office, keeping a link to Miami-South Florida's point forecast map on his Web browser's toolbar, on which he can click to get a general forecast of the week's weather. (Similar maps are available for every locale in the country from NOAA's Southern Region Headquarters' page at: As the summer storm season approaches, Smith monitors the graphic watches, outlook, and daily reports at NOAA's Storm Prediction Center ( These provide a quick visual reference of any activity that might affect a given area of the country. "If I see anything on the maps, I investigate the discussions," Smith explains.

Discussions of all of the weather warnings consist of cryptic text describing the exact nature of brewing storms. (For help deciphering these messages, you may want to refer to NOAA's list of acronyms at: Mostly, Smith says, he is looking for "SVR TSTMS" — severe thunderstorms — common during the summer and fall. According to Dan McCarthy, a warning coordination meteorologist at the Storm Prediction Center, thunderstorms are more dangerous than most people realize. "After tornadoes, lightning is the number one weather killer," says McCarthy. "Because lightning doesn't cause mass destruction like a tornado or a hurricane, it gets far less attention than it should." — Clayton DeKorne


RISING SEA LEVELS? The Intergovernmental Panel on Climate Change has estimated that the global average sea level has risen 4 to 10 inches in the past century, and predicts that sea levels will rise 8 to 34 inches by the year 2100. While that won't cause an inundation quite like that envisioned in "The Day After Tomorrow," it will result in accelerated erosion. Along much of the eastern seaboard and Gulf coasts, a 1-foot elevation in sea level can result in 150 feet of landward erosion.


By now most builders know that the newer pressure-treated woods — Alkaline Copper Quat (ACQ) and Copper Azole — attack ordinary galvanized hardware. But what's the alternative? Use only Type 304 or 316 stainless-steel fasteners with the new treated woods along the ocean, advises the Southern Pine Council.


In hurricane zones, the ultimate amenity may be a "safe room" — a concrete shelter within a home built to withstand winds up to 250 mph. FEMA's "Taking Shelter from the Storm" provides complete instructions for building one. For more information, contact FEMA at 888-565-3896;