Frequently asked questions



Service & Support


What are perms?

It is a measure of vapor permeability. A high number means a lot of vapor can get through. A lower number means less can get through. In weatherproofing, we want some moisture vapor to be able to move through a weather barrier so when moisture is generated inside a structure it can evaporate to the outside. Too much permeability, however, increases the likelihood that moisture vapor can also come into the structure. Building scientists recommend the “sweet spot” at 5-20 perms for weather-resistive barriers.

What do sound ratings mean?

There are 2 types of sound ratings. STC and IIC. Sound Transmission Class (STC) measures how much a product attenuates airborne sounds. A higher number means you are less likely to hear your neighbor’s TV blaring through the wall of your apartment. Impact Insulation Class (IIC) is a measure of the sound vibrations transmitted through flooring. A higher number means you are less likely to hear your upstairs neighbor tap dancing on hardwood floors. Sometimes you will also see “Delta” listed. This number shows the amount of sound reduced—the difference between using the product and using no product on a given surface.

What is the difference between service temperature and application temperature?

“Service temperature” is the expected temperature that a product will experience when it is in use. Remember that the inside of wall structures, particularly with dark colors and sunny exposure, can get significantly hotter than the outdoor air temperature. “Application temperature” is the air/surface temperature when a product is installed.

What is the difference between trapezoidal tear strength and tensile strength?

Tensile strength measures the force required to pull a material apart. The trapezoidal tear test measures the force required to continue a tear that is already started. Both measures provide an indication of durability.

What products can be used for air barriers?

When properly installed, both WeatherSmart and WeatherSmart Commercial are effective in an air barrier installation. Use our “Air Barrier Installation Guide”, or the installation method provided by a licensed professional.

Is Jumbo Tex an air barrier?

When installed in a specifically designed and constructed wall, Jumbo Tex may be used as part of the wall system to help reach the air barrier requirements. However, Fortifiber recommends using WeatherSmart Housewrap or WeatherSmart Commercial with Fortifiber Sheathing Tape when an air barrier system is required. See Fortifiber’s “Air Barrier Installation Guide” for additional information about air barrier requirements.

Do products meet/qualify for California Title 24?

California Title 24 is the state energy code. All of Fortifiber’s products can be used with California Title 24. Where the weather-resistive barrier is required to also perform as an air barrier, Fortifiber recommends the use of WeatherSmart Housewrap or WeatherSmart Commercial. Consult your design professional for how to meet the requirements of Title 24.

I need high temperature flashing, what should I use?

FortiFlash Butyl is a good option. It can withstand up to 250°F.

I need cold temperature flashing, what should I use?

FortiFlash Butyl can be applied at temperatures as low as 25°F. Once installed, it can withstand temperatures as low as -40°F.


Do I need to tape all the edges when I install a weather-resistive barrier?

When properly installed, seam tape is not required for weather-resistive barriers. However, it is a good practice to seal vertical seams with Fortifiber Sheathing or Commercial Tape. To create an air barrier, all seams need to be sealed. (See Air Barrier Installation Guide for details.)

What kind of fasters should I use?

The fasteners required to properly install Fortifiber’s weather-resistive barriers and mechanically attached flashings will vary depending on the jobsite conditions and exposure levels. Fortifiber recommends using an exterior grade corrosion resistant fastener for any location that may be in contact with water. A cap fastener can be used to provide a larger head surface to prevent tearing of the products. This is important for products that will be exposed for longer periods of time prior to being covered by the exterior cladding. It is up to the installer to determine the best fastener and spacing to use for their project.

Do I need to use sealant?

The use of sealant in a window install is a best practice to ensure maximum gap-free adhesion. Unless you are using a complete system like the one Fortifiber offers, you need to be sure to test any sealant with the other materials you plan to use, as compatibility may be an issue. To qualify for the FortiShield 15 year warranty, you need to use our sealant, and Fortifiber guarantees its compatibility with all other Fortifiber products.

Do I need to use primer?

Primer can increase adhesion to rough or irregular surfaces. It also improves adhesion when the temperature drops. You can rest assured that Fortifiber Primer is compatible with other Fortifiber products. See the data sheet for the particular product you are using for more detailed priming recommendations.

Which sealant should I use?

Compatibility of products is of critical importance. All Fortifiber products have been tested to be compatible with each other. Our 15 year FortiShield warranty requires use of Moistop Sealant and Liquid Flashing. If for some reason you choose to use a different sealant, be sure to test for compatibility before you install.

How long can I leave it up before it should be covered?

UV light exposure can damage the water resistant properties of materials over time. All Fortifiber products are highly durable, but we recommend prudent exposure periods to ensure optimum performance. We also recommend that you use good judgement for the exposure and season; one day in a hurricane is much more threatening to the products than 4 months of mild weather.

What can I use behinds stucco?

In most installations, two layers of a vapor permeable weather-resistive barrier are required, or recommended, when installing exterior three coat stucco. Any of Fortifiber’s weather-resistive barriers can be used as the back layer, closest to the wall framing, of the two layer system. Fortifiber recommends that the exterior layer, applied over the top of the back layer and against the back of the stucco, be a layer of Jumbo Tex or Super Jumbo Tex 60 Minute. These Grade D building papers are well suited for installation behind stucco. In many areas, the two layers can be installed using one of Fortifiber’s two-ply products. Fortifiber offers Two-Ply Jumbo Tex, Two-Ply Super Jumbo Tex 60 Minute, and Hydro Tex as labor-saving products that apply two layers of weather-resistive barrier at once. Check with your local building official to determine which two-ply products are available for use in your area.

Can I use your sealant/flashing with vinyl flanged windows?

There are two types of vinyl flanged windows, rigid and flexible. Vinyl windows typically include a rigid flange that is manufactured as part of the frame of the window. The flange on a rigid window can bend slightly, but can’t be bent significantly without damaging the flange. Think of trying to bend a credit card. A flexible vinyl flange window has a much more flexible flange and is often snapped into the window frame after it is manufactured. The flexible flange can be bent into a 90° angle and back without damaging or deforming the flange. Flexible vinyl is similar in flexibility to sheet vinyl flooring. All of Fortifiber’s flashings and Moistop Sealant can be used with rigid vinyl flanged windows. However, when installing a flexible flanged window, Fortifiber recommends using FortiFlash Butyl and Moistop Sealant, or a mechanically attached flashing, such as Moistop neXT or Moistop PF with Moistop Sealant.

What can I use behind cement siding?

Any of the Fortifiber water-resistive barriers can be installed behind fiber cement siding with excellent results.

I'm installing an entry door, which installation method should I use?

Door assemblies vary greatly, so there is no single best installation method. Please refer to the instructions provided by the door manufacturer.

I'm installing wood/vinyl windows. What installation method should I use?

When installing wood windows, check with the window manufacturer to see if they have any specific installation instructions. Fortifiber also has a wood window installation guide available on the website under the Window and Door Flashing section of the product page.

Do I need to do anything differently when I'm installing in cold weather?

It is a best practice to use a primer when the temperature drops below to the low end of the application temperature range. Primer will improve adhesion in these conditions. FortiFlash Butyl can be applied in temperatures as low as 25°F. We do not recommend installing adhesive products at temperatures below the installation temperature range.

What weather-resistive barriers can be used as an alternative to #15 felt meeting ASTM D226 Type 1?

All of Fortifiber’s weather-resistive barriers, including WeatherSmart, Ply Dry, Hydro Tex, Jumbo Tex, Jumbo Tex HD, Super Jumbo Tex 60 Minute, and all of the two-ply versions of these products are all approved alternatives to one layer of No. 15 asphalt felt complying with ASTM D226 Type 1 as required in Section 1404.2 of the IBC or Section R703.2 of the IRC. Fortifiber Building Systems Group holds an ICC-ES Evaluation Report, ESR-1027, which is available to help building code officials with identifying these products as code approved alternatives. This ESR report can be downloaded from or from the ICC Evaluation Services website.


Service & Support

How do I qualify for the warranty?

Unlike many products on the market, there are no special registration or proof of purchase requirements to qualify for the warranty. You just need to use all three steps of the complete Fortifiber system:

  1. A qualified Weather-Resistive Barrier (excluding Ply Dry)
  2. Flashing
  3. Moistop Sealant and Liquid Flashing

A code inspector needs information-how do I make sure he gets it? Please call (800) 773-4777 and ask for technical support.