Not All Bitumen Flashings Are Appropriate For All Walls

In the last ten years, self-adhesive flashings (SAFs) have become the predominant flexible flashing product for windows. Their ease of installation and self-sealing characteristics make them popular in all regions of the country. Rubberized asphalt (“RA” also known as bitumen) is the most widely used SAF product because of its lower cost. Much has been written about sealant compatibility and installation of RA products (see; but builders are now finding that RA products may not be suitable for all climates.


The temperature of the wall can depend on numerous factors, including (but certainly not limited to) the following:

  • The climate and sun exposure of the building elevations (southern, northern etc.)
  • The sheathing material (OSB, gypsum-based etc.)
  • The color and type of exterior cladding (fiber cement siding, wood siding, shingles, stucco etc.)
  • The installation techniques (fastener torque/pressure, sealing of siding joints etc.)

It’s not uncommon for south-facing walls in hot climates to generate internal temperatures which are beyond the service temperature of many rubberized asphalt products. Fortifiber publishes “application” and “service” temperature ranges for its rubberized asphalt and butyl flashing products. The application range shows the suitable temperature range for the initial adhesion of the product (and sometimes a primer may be necessary) while the service range shows the suitable temperature range for the proper long-term performance of the product in a wall system.

Which flashing is right for my project?

You can generally count on a higher price for a flashing product with a broader temperature range, but extreme temperature climates may demand a more robust product. Mechanically-attached flashings such as Moistop neXT® and Moistop PF® can provide an economical alternative to the more expensive self-adhesive flashings with comparable performance and no temperature concerns. Visit or call 1-800-773-4777 for information on Fortifiber’s full line of self-adhesive and mechanically-attached flashing products and accessories.

FortiFlash® 40° F to 120° F -40° F to 149° F
FortiFlash® 40 40° F to 120° F -40° F to 149° F
FortiFlash® Commercial 40° F to 120° F -40° F to 176° F
FortiFlex® 45° F to 120° F -20° F to 149° F
FortiFlash® Butyl 25° F to 125° F -40° F to 250° F