Testing real-world conditions: To measure the
actual withdrawal strength of sheathing nails, researchers have
pulled thousands of individual nails out of existing
When Hurricane Andrew struck South Florida in 1992, it broke
through unprotected windows, blew off flimsily built roofs, and
turned weakly attached shingles into clouds of damaging
Lessons learned from the 200,000 damaged or destroyed homes or
businesses spurred big improvements not only in hurricane-resistant
building techniques and materials but also in on-the-ground
construction practices and code enforcement intensity. Hurricanes
in later years prompted further progress, and though Florida
remains the national leader, homes built along much of the Gulf and
East Coast today are unquestionably more hurricane-worthy than
those built two decades ago.
But large gaps remain.
Despite months of front-page Hurricane Katrina news coverage in
2005, building codes and enforcement practices continue to vary
greatly from state to state or municipality to municipality.
Moreover, surprisingly little is known about how hurricane winds
pull apart and drive rain into homes — and what affordable
measures can seal them tight. Plus, existing homes, which comprise
the majority of the coastal housing stock, may have few (if any) of
the hurricane protections standard in new homes.
Fortunately, a small community of building scientists at
universities and in the public sector is working to close at least
some of these gaps.
According to these experts, when it comes to storm surge flooding,
protecting new homes is more a matter of smarter public policy,
more conservative building site choices, and better construction
quality than new building science. The story, however, is different
for wind and wind-driven rain. New insights, from field
observations following land-falling hurricanes and laboratory
research at universities, are enhancing construction techniques,
materials, and building codes, these experts say.
"Twenty years ago, we couldn't do the work we are doing now because
it would have been impossible or cost prohibitive," says Forrest
Masters, an assistant professor of civil engineering and wind
researcher at the University of Florida in Gainesville, who last
year designed and built the world's largest portable wind machine.
"But technology has reached a point where we can create hurricane
conditions in a laboratory."
Taming the Wind
Wind, the core subject of today's most fast-moving hurricane
research, is not the steady force often imagined — a
misperception only encouraged by the Saffir-Simpson Hurricane
Scale's categorization of hurricanes by maximum wind
"Wind to me," says Masters, "represents uncertainty."
The Saffir-Simpson scale describes wind speeds over open ocean. But
on land, low-level winds arrive in gusts whose forces and
directions are influenced by topography and the hurricane's
dynamics, Masters explains. What determines whether a house faces a
painless puff or a crippling body blow depends as much on intensity
as the placement of nearby structures, landscaping, and the
presence of micro-bursts, downbursts, or tornadoes, he says.
To simulate the erratic nature of hurricane-force winds, Dr.
Forrest Masters of the University of Florida developed this
Portable Hurricane Simulator designed to test the water-intrusion
resistance of full-scale building assemblies. Outfitted with a bank
of red "rain injectors," the monster bank of eight 5-foot-diameter
hydraulic fans can simulate wind-driven rain delivered at a rate of
44 inches per hour under air pressures of more than 35 psf —
as close to real-world hurricane conditions as any test apparatus
Getting a handle on wind's complexities is important because most
tests for product standards, such as those used by Factory Mutual
and ASTM International, consider wind a static, uniform pressure,
notes David Prevatt, another wind engineer at UF.
"As anyone who has ever been through a hurricane knows," he says,
"wind is anything but static, and anything but uniform."
Accurately portraying wind and its influences on homes is a
daunting challenge, in large part because the focus of greatest
interest — a real house facing a real hurricane — is
also the most dangerous to observe. But Masters, Prevatt, and
fellow wind-engineering researcher Kurt Gurley are taking what they
call a "wholistic" approach: laboratory experiments, field
experiments and observations, and post-hurricane wind-damage
One goal is to improve the testing methodology at the heart of
codes and standards.
As part of an initiative called the Florida Coastal Monitoring
Program, the researchers measure hurricane wind speeds and other
variables using portable towers erected in the path of land-falling
storms. They also collect measurements from hurricane-buffeted
homes equipped with pressure sensors, among other devices.
The team started chasing hurricanes in 1988 and has gathered data
from 18 storms so far. According to Prevatt, the researchers are
now checking this data against the equivalent measurements obtained
with scale-model homes in wind tunnels — measurements that
have long been the basis for the American Society of Civil
Engineers (ASCE) wind-load provisions underlying the International
Building Code (IBC) and International Residential Code (IRC) and
have been widely adopted by cities, states, and
The Florida Coastal Monitoring Program, run by a consortium of
wind research universities, has set up portable weather towers
(left) in advance of every hurricane and tropical storm that has
made landfall in the southeastern U.S. since 2001. Combined with
data from sensors installed on houses near the predicted landfall
site (below), researchers have evolved a much more accurate profile
of the wind-pressure characteristics that buildings must survive
than was available from previous data collected from ocean buoys
Prevatt says the mean pressure coefficients in the field
observations and wind-tunnel experiments match, but that the wind
tunnel may underestimate peak loads on roofs.
"The fact that the means are tracking fairly well is a sign that we
are modeling the macro, overall loads appropriately," he says.
"However, there is a question of whether we are actually capturing
Prevatt stresses that more research is needed before drawing
conclusions, but confirmation could encourage revisions of the ASCE
The researchers also examine the performance of building
components, such as windows, doors, and soffits.
In a project headed by Gurley, the team scrutinized how 200 homes
held up against the four 2004 Florida hurricanes. Among its
conclusions: While homes built to Florida's then-most-recent 2002
code sustained less damage than earlier homes, soffits were a major
point of failure. Wind damaged or blew out soffits, allowing
wind-driven rain to enter the attic, soaking insulation, collapsing
ceilings, and ruining interiors.
The 2007 Florida Building Code, the most recent version, requires
soffits designed to withstand the same wind pressures as walls,
Masters says. At this point there are no prescriptive measures for
how soffits should be detailed. However, the UF research has helped
builders develop better soffit-building methods, which relies on
strong blocking behind soffits rather than just J-bead (see
"Securing Soffits," January/
February 2007; www.coastalcontractor.net).
The UF team is also seeking to identify the most important upgrades
for existing homes built with no or few hurricane protections. They
use the hurricane wind machine, pressure-measuring nail-pullers,
and load sensors suspended from cranes to assess the performance of
homes built before Florida's first Andrew-inspired codes in 1994.
Prevatt says findings confirm that many such homes have extremely
weak roof-to-wall connections. Metal connections that transfer the
load path from truss to plate to studs to ground are essential.
However, retrofitting these connections, as any remodeling
contractor knows, is usually easier said than done.
"One needs to find a way in which you can attach [connectors] on
the interior and exterior faces without removing things, but it's
not easy," Prevatt notes.
Keeping Attics Dry
The improvements that followed Andrew — shutters or
impact-resistant windows, for example, and nailed rather than
stapled shingles — took care of the most glaring
home-construction deficiencies in new homes.
Since then, engineers and building scientists have been focused on
the "next weak link," in the words of Tim Reinhold, director of
engineering and vice president for the Tampa-based Institute for
Business & Home Safety. After the 2004 Florida storms, that
weakness was a home's ability to resist water intrusion.
Using sensors to measure the uplift force, researchers test the
resistance of framing connections in houses slated for demolitions.
The results will help determine the real-world performance of
retrofit connections needed to strengthen older homes.
Many homeowners complained of soaked carpet or moist drywall
despite roofs and walls remaining intact. The water not only seeped
through soffits, windows, and doors: it entered through gable-end
vents as well. When enough shingles disappeared, rain also poured
through gaps in intact roof sheathing.
What's needed, Reinhold says, is a moderately priced "backup
system" — a modification that would keep most of the rain
out, for a long enough period, to allow homeowners to repair the
roof or to cover it securely. Otherwise, he says, even with little
apparent exterior damage, homeowners may face complete renovations
One potential solution is to cover the joints in the plywood
roofing sheets with water-shielding tape during reroofing jobs. A
second is to spray closed-cell foam on the underside of the roof,
As for attics, Reinhold says the 2004 Florida storms also showed
wind could blow off ridge vents, leaving "a nice big place for
water to pour into the attic."
Florida's code now requires the vents to withstand the same design
pressure as the walls. But Reinhold says installing vents —
and soffits — per the manufacturers' guidelines is critical.
Most manufacturers recommend that workers install soffits against
wood backing strips, but installers sometimes ignore the
recommendation because the work requires a carpenter, he
Reinhold adds that homeowners can avoid worrying about vents and
soffits entirely by building sealed attics, with no vents or other
penetrations. While unusual in the past, sealed attics are becoming
more common, thanks in part to closed-cell foam insulation and
better understanding of the need to seal thermal bypasses (see
"Insulation That Works," January/February 2008;
No matter how well homes may be fortified against wind and
wind-driven rain, all are essentially defenseless against another
hurricane danger: storm surge.
"Wind, we build buildings to resist," says Chris Jones, a Durham,
N.C.-based engineer and consultant who co-wrote the current edition
of the Federal Emergency Management Agency's Coastal Construction
Manual. "Flood, we build them to avoid."
Storm surges flood structures in their path, batter them with
waves, tug at them with currents, and slam them with floating
debris. Their awesome destructive power was obvious in the
aftermath of Hurricane Katrina, which destroyed an estimated
300,000 single-family homes in Louisiana and Mississippi.
"Raise it or lose it" summarizes the basic tenet of new home
construction along the Gulf Coast in the aftermath of Hurricane
Katrina's surge topped base flood elevations by as much as 15 feet
in coastal Louisiana and Mississippi and produced the highest storm
surge recorded in U.S. history (27.8 feet in Pass Christian,
Mississippi). Below-sea-level New Orleans was a special case, but
in Mississippi, the result was "tens of thousands" of homes lost to
surge alone, Jones reports.
Unlike the case with wind, Jones says, few new materials or
research-inspired design advances will change the traditional
approach to surge: elevating homes, or placing them atop ground
high enough to remain clear of flooding.
"I think we've known for decades what to do," he says. "We just
don't always do it."
That said, there is growing recognition in some coastal regions
that homes may be exposed to harsher flood conditions than long
thought, he notes.
As a result, there is some possibility that more "A Zone" homes may
be built to tougher "V Zone" standards. "V" zones are threatened by
fast-moving waves 3 feet or higher, while "A" zones are areas where
such waves are not expected or are less than 3 feet.
Slab after slab was wiped clean, as the surge of Hurricane
Katrina advanced along the Mississippi coast near Gulfport.
According to a December 2005 report by the National Hurricane
Service, the maximum high-water mark was 27.8 feet at Pass
Christian, just west of the area shown (above). The surge
penetrated at least 6 miles inland in many portions of coastal
Mississippi and up to 12 miles inland along bays and
The National Flood Insurance Program, which underwrites all coastal
flood insurance policies, is trying to toughen coastal homes by
providing discounts to communities who switch to V zone standards
in A zones, Jones notes. New flood insurance rate maps, meanwhile,
make it easier for builders to locate the most vulnerable region of
the "A Zone," ending one source of past difficulty, he
Whether or not those inducements work, Jones says he always
encourages builders to be conservative, building higher and
stronger than the code allows.
It's an admonition with relevance for the coastal building industry
and construction related public policy in general. That's because
the research and recommendations of building scientists like
Reinhold, Masters, and Prevatt represent only part of the solution
to fortifying homes. Responsibility also rests with the elected
officials, regulators, builders, and inspectors, who control
everything from where homes are built to quality of workmanship to
maximizing compliance with codes.
Before Katrina, Alabama, Louisiana, and Mississippi lacked
statewide building codes for residential structures. Three years
later, Reinhold notes, Alabama has yet to adopt a statewide
residential building code. Mississippi, which lost 68,729 homes to
Katrina, now requires coastal counties to enforce the 2003 IBC and
IRC, but enforcement is questionable, Reinhold says. Louisiana,
where 283,838 homes were destroyed, today requires the latest codes
"but they are struggling trying to get up to speed on getting
building departments in place and enforcing the code," Reinhold
Says Reinhold, the only solution to protecting coastal homes "is
through mitigation and making sure we build as smartly as we can.
We need to give these buildings the best chance we can of going
through these storms." ~
Aaron Hoover writes about science and the
environment from his home in Gainesville, Fla., and is a regular
contributor to Coastal Contractor.