A Closer Look at Gypsum-Fiber Roof Board: Why Does It Move? (How Is DEXcell®
BRAND Coverboard Different From Competing Coverboards?)
–From DEXcell’s Above Board newsletter, Fall 2017
Two roof boards, manufactured by two different companies, may be compared to one another, but they are worlds apart when one board has “fiber” and the other does not. The materials that comprise a gypsum coverboard make all the difference in how it reacts to the elements, like fluctuations in humidity, condensation or moisture from a leak. Since 1986, inorganic fiberglass mat coverboard (and sheathing) has proven its ability to perform well under the harshest of weather conditions. National Gypsum’s DEXcell®BRAND Roof Boards are comprised of inorganic materials – and that sets us apart from some competitors’ boards. It is our great differentiator: fiberglass and gypsum, which has the same moisture expansion and contraction properties as steel or concrete, will not cup or bow. This has given our products their stability. On the flip side, when a roof board contains paper fiber, even a small amount, its long, cylindrical cells will expand and move, resulting in edges compressing each other and eventually cupping. Another issue: Even if a contractor properly gaps a gypsum-fiberboard, it can swell up at the edges or allow solvent-based adhesives to flow under the coverboard. This can deteriorate some insulation and lock in vapors that could lead to blisters later on. Regardless of how you market it, you cannot change the facts surrounding the components (or fiber in the gypsum board) –paper will do what paper will do. There’s just no way around it.
Building Envelope Specialties 