Monday, December 12, 2011
Spray Foam Adhesives Strengthen Your Building’s Roof (Part 1)
More and more hurricanes continue to slam to the U.S. eastern coastline each year. In the past decade, billions of dollars worth of property damage and lost lives have prompted research and product development to help prevent this continued destruction to our homes and businesses.
Since 1989, over $130 billion in losses were filed due to hurricane related insurance claims. A startling $85 billion of destruction occurred in 2004 and 2005 alone. A large percentage of these losses were directly caused by severe wind and rain exposure from failed roof decks, according to a 1998 study by Clemson University. Many of these roof deck failures can be traced to outmoded nailing schedules or poor workmanship. Even well constructed roofs are often sorely unqualified to deal with the kind of weather extremes experienced in the southeastern coastal states.
Spray polyurethane foam (SPF) is most widely known for its superior energy saving insulation qualities in residential and commercial building. Unknown to many folks, is that spray foam (like the one made by Conklin) is also being used a construction adhesive to make residential roofs stronger and resist the wind and water damage effects of hurricanes and high winds.
Roof uplift is the main threat to an overhanging roof in a high-wind event. In hurricane force winds, roof system failure occurs when the roof cannot withstand the uplift pressure exerted on the eaves and overhangs. When the wind is blowing perpendicular to the ridge of a roof, positive pressure is created on the windward side and negative pressure is created on the other side. This produces high uplift forces in these areas, which can cause all or parts of the roof to blow off.
In this application, spray foam is applied from inside the attic to the underside of the roof structure. Specifically, the SPF is applied into the corner areas where the joists (trusses) meet the roof sheathing. Instead of traditional ”one-point” adhesion from just the nails through the sheathing, there is now ”three-point” adhesion. This comes from the nails at the top, and foam adhesive that spans nearly three inches down the joist and out onto the sheathing, on both sides of every joist. The foam adhesive also runs the entire length of the joist in a continuous glue-like bead, or fillet.
The spray foam adhesive creates a tenacious bond between the roof sheathing and joist structure that helps to resist and protect the roof structure from severe winds.
According to tests conducted in 2007 by the University of Florida and various spray foam manufacturing companies, spray foam provides up to three to four times the amount of uplift wind resistance over roof construction that uses nails alone.
* Please check back for Parts 2 and 3 of this blog post series. *
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