|More Strength= Less Damage,
along South Carolina Coast
"If you build it, they will come". Yes, that is a line from the Kevin Costner movie
"Field of Dreams", but it can also apply to that of the building
of homes along the South Carolina coast.
Let's go back to September 21st 1989. It was 11:30pm as a Hurricane Hugo rolled into the
Charleston Harbor with a point to prove. And that point was that anything in its way
would be destroyed. At landfall Hurricane Hugo a Cat 4 hurricane on the Saffir Simpson
hurricane scale packed winds of 140 mph and a pressure of 934mb. Hugo caused 10
billion dollars in 1998. However in today's money that would equate to 16.6 Billion Dollars.
The home I lived in at the time had 15 trees that were totally destroyed along with $27,000 worth of
damage to the house. Even though I was in the SW sector of the Eye, the strongest winds recorded
in my area were 109mph winds. Sustained winds of 100 mph on a flat surface will result in the
pressure of 50 pounds per square foot or 50psf. The NE sector of the hurricane normally has
the strongest winds. In the case of Hurricane Hugo, the strongest winds at the time of
landfall were 140 mph. As the pressure of a hurricane increases in strength, so do
the pounds per square foot of pressure on structures. There is a vast difference in
damage between a Cat 2 hurricane and a Cat 4 Hurricane. By increasing winds from
100 mph to 150mph, the surface pressure will double from 50psf to 100psf. With
a Cat 2 Hurricane there will be some damage to building roofs, doors and windows. There
will also be considerable damage to mobile homes. Flooding will occur and small to medium
trees will be blown down. The more powerful Cat 4 Hurricane will result in more extensive
curtain wall failures. You will also see some complete roof structural failure on
small businesses. Gas station canopies and overhang structures will be blown away
or ripped from their foundations. There will complete destruction of mobile homes
and weak structures. Along the coast, there will be major beach erosion and flooding
will be experienced well inland depending on topography.
Since 1990 there has been a tremendous increase in growth, development and population along the South
Carolina coast. This can be seen in the three coastal counties of Horry, Beaufort, and Charleston
County. Horry County is home of over 150 golf courses and is within a 30 minute drive of downtown
Myrtle Beach. Since 1990 Horry County has seen a 58% increase in population growing from 144,000
to 226,000. The southern most coastal county is Beaufort County, home of Hilton Head Island, which
is one of the South East's most popular resort areas. Beaufort County has seen a population
increase of 60% from 1990 to 2005. Their population grew from 86,000 to 137,000 during that
time period. And finally we have Charleston County, which includes the barrier resort
islands of Kiawah Island, Sullivan's Island and the Isle of Palms. Charleston County has
seen their population increase 12% from 295,000 to 309,000 during the years of 1990 to 2005.
Along with these increases in population have come increases in home values. The Charleston Chamber
of Commerce and the Myrtle Beach Chamber of Commerce state that Charleston County has seen a 120%
increase, and Horry County has seen a 115% increase in property values from 1996 to 2005.
South Carolina has over 150 Billion dollars of insured coastal properties which by the way is the
8th largest in the nation. So with that being said, how does one better protect a home that is
already built along or close to the coast? And how does one build a new home that will withstand
hurricane winds? Lets first start with an existing home. Impact resistant windows are a great
start. These are windows that are made of double pain impact resistant glass with an inner
shatter proof membrane. This is similar to the glass that we use in cars. The windows are
tested to withstand a projectile hitting the glass at 150 mph. The glass may break, but
the membrane will hold the glass in place keeping it in the heavy duty aluminum framing. If
a window is broken out of its frame, it will provide a point of entry for wind to enter the
house. This increases pressure in the house and then the wind must find another way out. "When
a building envelope is breached, the difference in air pressures inside and out will
cause a building to loose a roof or a wall and when that happens, the building is
done for," says Brian Hedlund, national product marketing manager for Jeld-Wen Windows
& Doors. The only way to protect against damage from wind entry is to keep it out. This means
deflecting wind and driving it around the building.
Another way to protect your home is by sealing the roof. If you have a shingled roof, the wind may lift the
shingles along the roof edges. By caulking along the edges, where the shingle touches the wood frame, you
not only seal the roof from water damage on the location, but you also will give more strength to the
single. This added strength will deter winds from lifting the shingles. Once the shingles begin to
lift due to strong winds, they will continue to lift over the rest of the roof.
If you have a gabbled roof, installing additional braces of galvanized metal hurricane strips in the
trusses and at the gable ends will increase the structural strength. The main focus on strengthening
your home is to start from the bottom and go up. All structure must be tied or fastened together. One
of the least expensive ways to strengthen your home is to install heavier bolts on doors along with
bar braces for entrance doors and garage doors as well.
New construction may vary depending on how far you are from the coast. If you build on the coast, you
will want to be elevated at least 20ft. above mean high tide. This may be done on steel beams, reinforced
rebar (steel rods) through cinderblock, and or wood pilings. Tying all areas together with hurricane
strips will be the best way to minimize structural damage. If you are building away from the coast,
the foundation again is the most important first step.
The picture below shows a foundation of new home with starter bars sticking up. They are used for
blockwork wall reinforcing. The foundation is two feet in thickness below the surface. Cinder blocks
are lowered over rods. 16 mm cast iron holds down bolts which are installed into the cinderblocks. The
cinderblocks are filled with cement.
The picture below shows a foundation of new home with starter bars sticking up. They are used for blockwork
wall reinforcing. The foundation is two feet in thickness below the surface.
Cinder blocks are lowered over rods. 16 mm cast iron holds down bolts which are installed into the
cinderblocks. The cinderblocks are filled with cement.
Final step for the foundation is to install Hold-down bolts to truss connection. Notice also metal
bands that are attached from 2x4 to 2x4
Hurricane proof windows and doors along with a well enforced roof (7/8" or greater treated plywood
and 30 year shingles) will complete a home ready for hurricane force winds up to a Cat III and greater.
For many years, homes were built as FHA 235 standards, which used 2x4 on 24" centers. These
homes could only withstand winds of about 70-80 mph. Many homes constructed along the coast
today are built to withstand winds of 130-150mph. More expensive to build, but less to
replace when the winds come. Sometime peace of mind is priceless.
South Carolina Omnibus Coastal Insurance Reform Legislation