What's the Difference: Self-adhesive flashing
Using butyl-based or rubberized asphalt-based depends on temperature, location
Applying self-adhesive flashing around windows, doors, vents, electrical outlets, and other vulnerable areas of a house is an effective way to help prevent moisture and air infiltration. Typically sold in rolls of varying lengths and widths, self-adhesive flashing is most-commonly available in two versions, those that use a butyl-based adhesive and those with a rubberized asphalt-based adhesive.
Temperature ratings vary by brand, not adhesive type
By manipulating the adhesive compound, manufacturers of butyl- and asphalt-based flashing have the ability to control the temperature at which their products best perform. The development process comes with trade-offs, though. Flashing created for use in cold weather doesn’t remain stable at extremely high temperatures. Conversely, as high-temperature resistance is increased, cold-weather adhesion suffers in both butyl- and asphalt-based flashing.
Butyl, however, can be made to withstand much-higher temperatures than rubberized asphalt. For this reason, butyl is often used to create flashing for extremely hot climates like the desert southwest, where building-surface temperatures can reach staggering levels.
Cost: (6 in. by 75 ft.): $45 to $55
Rubberized-asphalt flashing can’t be used everywhere
Asphalt flashing has compatibility problems with flexible polyurethane sealants, certain roofing membranes, and nonintegral PVC window flanges that are found on some wooden windows. These materials contain plasticizers, which are chemicals that help to make them flexible. When the rubberized asphalt comes in contact with the plasticizer, a chemical reaction takes place, and the adhesive liquefies, compromising the flashing’s ability to perform properly.
It’s important to note that not all PVC causes a chemical reaction. Rigid PVC, found on most windows, does not contain plasticizer and performs seamlessly with asphalt flashing. Check with the window manufacturer prior to using this flashing to determine whether the product contains plasticizer.
Cost: (6 in. by 75 ft.): $25 to $35
Top photo: Courtesy of Fortifiber; bottom photos by: Krysta S. Doerfler