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Hurricane Hugo: Building methods have made structures more durable in 25 years since the storm
By Jason Lesley
Robert Cox went to work for Georgetown County just weeks after Hurricane Hugo struck in September 1989.
Now the county’s chief building official, he has seen building standards evolve to make houses in hurricane zones less vulnerable to wind. The building techniques being employed on beachfront houses today use mathematics and science to keep them in place when the next big blow strikes.
Cox remembers seeing houses that floated off their pilings into Pawleys Creek 25 years ago. He examined a house under construction on Myrtle Avenue in the middle of Pawleys Island this week and pointed out design changes that will hold it together in all but a cataclysmic storm. “If you could put a hook on top and lift that house by the roof,” he said, “it would all stay together. That’s called continuous tie.”
Hugo got insurance companies and builders to thinking, Cox said, but it was Hurricane Andrew hitting Florida just south of Miami that changed standards nationwide.
“What caused these houses to have their roofs blow off and walls collapse? he asked. “They started picking up the roofs on the ground and looking at them and found no tie-down straps to walls at all except for toe-nailing, or they found clips that had one or two nails. It’s not the clip that gives the resistance. It’s the number of nails. You can get a clip that says it will withstand thousands of pounds of uplift, but if you’ve got 16 holes and only put two nails in it, it’s no good.”
Today’s technique calls for framing to be completely sheathed in plywood. Before Hugo, Cox said, only the corners of new houses were sheathed in plywood, and either black felt board or blue insulation board connected them.
“Science came out with the numbers that said how to manage wind loads,” Cox said. The pilings, the floor system, the walls and the roof are all tied together. “That’s when the wrapping in plywood became popular,” Cox said, “and the nail pattern meant something.”
Carpenters abandoned previous habits of putting a few nails to hold a sheet of plywood in place to putting nails every 6 inches. “There’s resistance there that holds plywood together if you nail it right,” Cox said. “Builders went from ‘Let’s nail them good’ to a lot of science and mathematics.”
That thinking extended to the design itself. The size of the overhang made a difference in the uplift force. New houses on the beach don’t tend to have roofs that overhang their walls very far. “It’s math, not guesswork,” Cox said.
A saltwater environment presents additional problems. Straps, nails and bolts all rust unless they are galvanized or stainless steel. “In the old days, they would buy any kind of strap,” Cox said. “Now there’s a strap for everything calculated on the amount of uplift.”
Cox has seen standards rise from resisting 80-mile per hour winds to 130. Pilings have to be deeper. Even the type of framing lumber changed. “Southern yellow pine will grab that nail and you can hardly take it out with a hammer. Put it in soft wood, and all of a sudden the strap is doing no good,” he said.
Improvements in windows came along around the year 2000. “You don’t want the windows to blow out,” Cox said. “They set windows up and shot 2-by-4’s at 100 miles per hour.”
The new house on Myrtle Avenue will survive high winds better than most, Cox predicted. “If this one goes,” he said, “there won’t be anything left.”