SEA 



SCIENCE 



Spent t-r Rogers 



Likewise, buildings don't 

 simply blow over in the wind, as 

 many people imagine, Rogers 

 says. The damage is most often 

 caused by inadequate connections 

 and the wind's forces of uplift. 



Wind uplift forces cause 

 airplanes to fly, and the same 

 principle applies to roofs. When a 

 high-speed wind blows across a 

 low- to moderately sloped roof, it 

 creates a lift. The roof pulls off 

 when the lift force exceeds the 

 roof s weight plus the capacity of 

 its connections to the walls. 

 Without the roof, the walls 

 collapse. But you can counter the 

 problem by using metal straps and 

 hurricane clips rather than nails 

 alone to secure the roof. Hardware 

 and building supply stores sell 

 these connectors, which cost as 

 little as a quarter each, and 100 of 

 them can tie down an entire house. 



"They can make the 

 difference between a roof that 

 might take off at 85 to 90 miles 

 per hour versus one that could 

 stand at 1 10 to 120 miles per 

 hour," Rogers says. 



Accessibility to the nooks 

 and crannies where straps and 



clips are needed will make the task of installing connectors easier in 

 some houses than others. The connections between the roof and the 

 top of the wall is often most important, but the overall storm 

 resistance is only as good as the next weakest link. To be effective, 

 the connections must extend from the peak of the roof to the bottom 

 of the foundation. But overconnecting a single link isn't worth the 

 effort if other links are weaker. Paying a professional designer or 

 knowledgeable contractor to check the building's weak links might 

 be worthwhile, Rogers says. 



Another uplift problem that caused major damage in Hurricane 

 Andrew in south Florida was insecure roof sheathing or roof deck 

 — the plywood that the shingles are nailed to. Since that's the 

 highest structural part of the building, it must be well nailed to the 

 roof framing. Typically, however, the buildings damaged by the 

 1992 storm had too few nails in place to properly hold the sheathing. 



The solution is simple: Add more nails. Normally a difficult 

 task, this becomes quite easy when shingles are being replaced. Just 

 ask the roofing contractor to inspect the nails and add as needed 

 before he installs new shingles. And while you're on the roof, 



Sheathing wider the eaves has been removed to allow 

 installation of straps between the rafters and exterior wall. 



Spencer Rogers 



Brackets have been installed. 

 These brackets will help the building withstand high winds. 



Rogers recommends other 

 techniques to improve the wind- 

 resistance of asphalt shingles. He 

 can provide these guidelines free. 



Below the roofline, 

 windows and doors are also 

 important to maintaining the 

 integrity of the building 

 envelope. Homeowners should 

 note how strong and well- 

 attached they are. French and 

 sliding-glass doors — with wide 

 spans and poor connections in 

 the middle — are troublesome. 

 And large picture windows and 

 double garage doors are often not 

 strong enough to survive fierce 

 storms. 



These are problems best 

 addressed before a storm arrives 

 because the consequences of a 

 broken window or door can be 

 dire, Rogers says. As wind enters 

 the house, it increases pressure 

 inside, which pushes up the roof. 

 Meanwhile, the forces of uplift 

 try to pick up the roof from the 

 outside. Combined, internal 

 pressure and external uplift can 

 overwhelm a poorly connected 

 building. 



Commercial shutter 

 systems can help prevent broken windows. Other less expensive 

 alternatives include temporary shutters made of plywood or metal. 

 Homeowners should make sure that temporary shutters are well 

 connected to the building, Rogers advises. 



"A poorly connected shutter is more dangerous than no shutter 

 because you have a large piece of wood flying around," Rogers 

 says. The American Plywood Association offers design guides on 

 its World Wide Web site at www.apawood.org. 



Ultimately, strengthening these connections and the building 

 envelope can pay off. Rogers says insurance claim losses due to 

 wind-blown water damage inside buildings are often three to seven 

 times higher than the cost of repairing structural damage. E 



Contact Rogers for free copies of a homeowner's guide to 

 hurricane retrofitting, Is Your Home Protected From Hurricane 

 Disaster? or Project Blue Sky's construction guidelines for asphalt 

 shingles. Call 910/256-2083 or write North Carolina Sea Grant, 

 Center for Marine Science Research, 7205 Wrightsville Ave., 

 Wilmington, NC 28403. 



COASTWATCH 33 



