Braving the elements: protection against hurricanes
One of the most hurricane-prone parts of the United States is south Florida, which has been hit by more than one out of every four hurricanes that made landfall on US territory in the period 1900-2000. Building codes in the state have long considered the need to mitigate damage from these extremely violent storms. Windows have been particularly vulnerable to damage from windborne debris such as gravel, roofing tiles, and more recently such objects as satellite dishes, which can be hurled against them by winds of up to 200 kph or more.
For most of the past 70 years, the preferred glazing technique used in this part of the state was wet glazing with a PVB-based glass laminate. This involves bonding the laminated glass to a supporting structure using a highperforming architectural sealant, usually silicone. Wet glazing however poses serious challenges. The level of precision and skill required to properly wet glaze a hurricane impact resistant framing system, as well as the specialized materials that are needed, make this an expensive and time-intensive option. What's more, if a glass panel subsequently breaks, additional labor is necessary to cut through and remove the existing adhesive, clean the framing system and re-apply new adhesive - a process that takes yet more time, further increasing costs to the end-user.
In real world applications, the performance of wet glazed systems is somewhat contingent upon skilled workers who understand and follow installation guidelines to ensure a strong structural adhesive bond. For example, if there is a time lag between the installation of the glass panels and the caulking process, dust and other contaminants have time to enter the seal and could affect system performance. Dry glazing with a structural interlayer eliminates this source of variability.
Dry glazing as a cost-effective alternative
Dry glazing with a structural glass laminate differs from other methods in that it relies on rigid, structural glazing interlayers like DuPont™ SentryGlas®, instead of PVB interlayers; such a structural laminate provides sufficient post-breakage stiffness, allowing the adhesive bonding to the framing system to be completely eliminated. This feature makes dry glazing a more economically competitive option than traditional wet glazed systems, since there is no need for the skilled labor that is normally required to apply the structural adhesive bond in the wet glazing scenario. Not only does this labor saving reduce costs, but it also reduces some of the performance variability that is common with wet glazing.
"With dry glazing, you are in and out quicker," explained Sid Miller of Miller Glass, "and your team can move on to the next project." He reckons that for his own company, with some 60 glazing projects a year, this improved flexibility has translated into significant cost savings. Compared to wet glazing in the field, the ease of installation is remarkable, Miller maintains. "A common complaint in our business is that good labor is hard to find. With dry glazing, however, there is no need to manage a team of skilled labor, and thanks to eliminating the entire silicone sealing phase, the speed of installation is greatly increased. We have found that it is possible to do perhaps 20 to 30% more work in the same amount of time. That clearly affects the bottom line." Since retrofits or repairs can be done quickly as well, without having to remove or replace bonding adhesive, here too the end-user benefits from reduced expenses. "Retrofitting can be done in one-third to one-half of the time it would take to restore a wet glazed system," said Miller. "It’s very easy to deglaze these units, which saves time for the contractor and the end-user." Finally, properly designed dry glazed fenestration systems can provide extremely high windload design performance, maximizing the allowable performance levels of laminated glass constructions.