Volume 6 Issue 7 August 2005
Attendees are Bowled Over by
Presented on WindBorne Debris Protection
by Alan B. Goldberg
Sanding room only, generally synonymous with special events, might be considered unusual for a meeting of architects, contractors, building officials and window and door manufacturers. That is, unless the topic is windborne debris protection and hurricane codes, as Oldcastle Glass and its cosponsors, Solutia and Weather Shield, learned recently. The meeting was held on June 22, 2005 in Destin, Fla.
"We could have had more than 200 people today, but the meeting room holds only 140. We had people standing," said Nanette Lockwood, market manager, specialty products for Solutia.
Exterior Building Materials
The program began with a presentation by Vinu Abraham, managing partner for Hurricane Testing Laboratory LLC in Riviera Beach, Fla. He said there are some typical effects from a hurricane:
• Flying debris breaks glass in the building;
• Wind and rain enter the building through breached openings;
• The formation of a 1 percent opening on a windward wall can lead to a 200 percent increase in pressure on the underside of the roof and a 50 percent increase in pressure on the exterior walls.
Abraham described impact and cyclic air pressure as two types of tests his company performs on samples of windows, doors, roofs and garage doors. The impact test involves three missile levels (depending on the degree of protection required by the standard test method being followed): a small cannon firing a two gram steel ball at 130 feet per second or 89 mph; a large cannon firing a medium, or 4.5 lb., 2 by 4 inch lumber missile at 40 feet per second or 27 mph; or a large can non firing a large, or 9 lb., 2 by 4 inch lumber missile at 50 feet per second or 34 mph.
The cyclic wind load test, which can last four to five hours, replicates the pushing and pulling forces of wind found during hurricanes. It applies to all uses of the building envelope for which windborne debris compliance is sought.
Abraham pointed out that the American Society of Testing and Materials (ASTM) and the Florida Building Code (FBC) standard test methods require two basic tests: a series of impacts to the entire assembly followed by the application of cyclic air pressure for several hours. He said both methods use a load spectrum comprised of 9,000 for several hours. He said both methods use a load spectrum comprised of 9,000 air pressure cycles for glazed assemblies which resembles the force of a hurricane.
Abraham outlined the pass/fail criteria for ASTM (E-1886/E1996) and the FBC (TAS201).
While explaining wind zones that have been established as a measurement for product performance, he said a product that meets the requirements of a particular zone does not necessarily mean it can be used anywhere.
“A product tested to the requirements of Wind Zones 1, 2 or 3, does not meet the requirements of Wind Zone 4 (the large missile test). But a product tested to meet the requirements of TAS 201 meets the requirements of all wind zones,” he said.
Abraham emphasized that products must pass both tests to be considered valid and that the tests evaluate the entire assembly.
“You get what you test,” he cautioned. “There is no substitution for components. No two interlayers are the same. No two structural sealants are the same.”
Describing glass fabrication, John Bush, director of laminated products and development for Oldcastle Glass, said the operation begins with large sheets of glass.
“We heat it, bend it, strengthen it, insulate it and laminate it,” he said.
Bush showed how laminated insulating glass is made and he defined each of the glass surfaces so architects would understand how to specify laminated units clearly. He reinforced Abraham’s message that products must be tested as a system and that a component cannot be changed without testing the entire unit. He also described and defined the interlayer types and their thick-nesses, referring to glass-clad polycarbonate as “the ultimate product.”
Wind Loading Criteria
Bill York who is president of WH Consulting Inc. and a teacher of hurricane preparedness classes at the University of Florida, asked the audience to identify the causes of failure from photographs of homes destroyed by hurricanes. They were: poor installation, sheathing failure, roof covering failure and cladding failure. Referring to pictures of garage doors that were blown out, he said they get pulled in and out from high winds because they are fastened at the sides.
York described the characteristics of hurricanes as increased wind speeds, wind gusts, slow-changing wind direction, storm surge, waves, extensive rainfall, tornadoes and atmospheric pressure change. He defined a hurricane as a special type of windstorm, gusting turbulent winds, changing slowly in direction and carrying wind-borne debris. Building designs must consider all of these forms as well as internal pressure, he said.
“When hurricane warnings are posted, watch the cone,” York said.
“Understand where you are in relation to the eye of the storm. The tidal problems are going East of the eye. Know what happens on your coast and where they come from. When a storm make landfall, the wind speed dies down because it loses its source of heat. Keep your eye on the storm because it will come back.”
He emphasized that hurricanes do not only take place in Miami-Dade counties but throughout the state, including the Panhandle. He showed a map of Florida pointing out recorded wind-borne regions and wind speeds (see map on page 25). What is felt on the ground is not as high as the winds at higher elevations. He showed a chart with various heights and the wind speeds from five to 33 feet, including building heights and the various wind speeds. He identified zones of wind and structural interaction as they relate to a structure.
For example, wall covering is zone one; eaves, zone two; ridges, zone three; and roofs, zone four. He said when wind blows on one side of a building, it causes negative pressure on the other sides, and can double the loads on the negative side, causing failures. He defined structures as being open, partially enclosed and enclosed to help architects meet specifications of the Florida code. Impact ratings vary with each region of the state, he said.
York emphasized the importance of following the same protocol from specification through installation.
“If you supply (or specify) a product and you use the Miami-Dade protocol, then you must install the product based on that protocol,” he said.
York briefly described the types of window covering from steel storm panels, which he said were the least expensive, to polycarbonate shutters. He added that damage to a building envelope is a critical factor and wind-borne debris must be considered in design.
An update on current legislation related to construction in the Florida Senate and House was provided by Kari Hebrink, Solutia’s legislative consultant. She mentioned House Bill (HB 835) which deals with wind-load protection and codes. It requires the Florida Building Commission to adapt the most current edition of the wind protection requirements.
State Senator Charlie Clary, who represents the Panhandle and is an architect, discussed a dilemma that is presently being reviewed—affordable housing versus the cost of adhering to strict building codes. Echoing concerns of the Florida Home Builders Association, he said, “We have to figure out how to make affordable housing affordable.”
Clary acknowledged that conforming to all the codes is difficult, yet there is a responsibility to do the right thing. He presented a brief history of hurricane damage in the region which, he pointed out, was mostly storm surge and not high winds.
“We evaluated everything and made a convincing argument that northwest Florida does not get the same wind speeds (as Miami-Dade) and that state building codes were based on impacts on those areas most severely affected.”
It’s all about the protection of property and insurance companies trying to minimize exposure; and this is understandable. But, he emphasized that damage from previous hurricanes in this area was due to storm surge.
“I think there is a fine line between our building code and protecting our citizens and making structures that are affordable,” he said.
These sentiments were also shared by Harold Owens, a local county building official. “Our problem is that we are being compared to Miami-Dade which is flat. We are 250 feet above sea level. The terrain is very different here.”
He said this was an issue that required continued discussion and more serious thought about affordable housing but with adequate protection.
When it was time for attendees to ask questions of the speakers, there were several. One person asked about wind loads over the roof, specifically gables and soffits.
“The building code will be modified prior to Oct 1, 2005 to address the construction of non-vented attics and the water intrusion issue,” said Jack Glenn from the Florida Home Builders Association.
In response to a question on base flood elevation, Glenn said there is consideration in the Panhandle for 16 inches to three feet. He said the Federal Emergency Management Agency is studying the issue.
In response to a question on the position of the laminate in a window unit, Bush explained that repositioning the laminate would have no effect on impact.
“The glass will still break,” he said.
He added that tempered or laminated glass can be used in an impact unit.
The meeting concluded with a demonstration by the Hurricane Testing Laboratory of a missile impact test using a standard window unit. In a nearby field, a cannon shot a wooden 2-inch by 4-inch missile, eight feet long, at the speed of 50 feet per second or 34 mph.
Judging by the success of its wind-borne protection sessions, the sponsors will continue to offer them in hurricane zones. It is a topic worth the time and a meeting worth attending.
Alan Goldberg is a contributing writer for DWM. He has more than 30 years of experience in the insulating glass industry.
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