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Know Your Metal Roof Underlayment Options

Best practices for selecting and installing metal roof underlayments

Mcn Kyp Firestone Oct17 1
Metal roofing systems bring beauty and functionality to a building, often acting as the first line of defense against moisture, and in some cases, even the spread of fire. Without a proper underlayment, which separates the roofing material from the roof deck, the roof and interior structure are exposed to potentially damaging elements including chemicals, resins and moisture. Selecting the right underlayment is vital for ensuring that the metal roof system performs at its best throughout the life of the commercial building. To reap the full benefits underlayments offer, keep these tips and best practices in mind prior, during and after installation.

Familiarize Yourself
Becoming familiar with the metal roof underlayment options available can help you decide what’s best for your commercial building. Whether you’re opting for a traditional underlayment, or a selfadhered option, the average life span of a metal underlayment will vary depending on the product that’s selected. In most cases, you’ll want to choose an underlayment that meets testing and code requirements, UL certifications and is available with a minimum 20-year warranty to ensure your building is protected long term.

Traditional underlayments, such as ones composed of asphalt-saturated felts or asphaltcoated fiberglass, can be much more labor-intensive due to their weight, and tend to deteriorate more quickly than rubberized products. Premium, self-adhering underlayments, however, are typically thinner and lighter than traditional offerings, making them easier to install. These products are made up of non-reinforced, rubberized asphalt, which provides excellent flexibility, adhesion and traction. Their skid-resistant material also creates a safer and more secure surface for maintenance workers and other rooftop foot traffic.

Prep for Installation
Once you’ve selected the proper metal underlayment, it is important to ensure the roof’s surface is prepped and ready for installation. It is imperative the underlayment is fully supported by a roof decking material, as underlayments aren’t meant to be used as the primary roof deck. Here are a few other important considerations:

Gather equipment: While there are no special tools needed for installing metal underlayments, keeping the following equipment on-hand can help streamline installation: knife for cutting, tape measure, heavy broom or roller, and rags.

Prepare the surface: Prior to application, make sure to sweep clean any and all debris from the surface of the roof. The roof should also be completely free of grease, water and moisture to ensure a proper bond. Additionally, all roofing materials should be stored in a clean, dry area in their original, unopened packaging at the manufacturers-listed minimum and maximum temperature range.

Refer to the manufacturer’s installation instructions: Installation may vary slightly depending on the manufacturer. In some cases, a primer may be necessary to ensure an adequate bond.

When installing a self-adhered underlayment, start at the lowest part of the roof deck, and install valley conditions first. Lay the underlayment flat in place with the print side up. The underlayment should then be cut to a length that can be easily managed; allow for about 3-inch side laps and 6-inch end laps. Next, diagonally peel half of the release liner off of the roll and install by applying heavy, even-hand pressure or using a broom from the center of the sheet toward the outer edges. Remove the remaining release liner from the other half of the roll and apply pressure in the same manner to ensure complete adhesion. In very steep-slope applications, back nailing may be recommended. In that case, it’s important to make sure all nails are covered by the next overlapping sheet.

Avoid Common Pitfalls
Knowing what common challenges can occur during installation can make them easier to avoid. For instance, not all underlayments can be installed at the same temperature. In general, application temperature can range from 40 to 140 F, depending on the product. Another important factor to keep in mind is geography. For example, if your commercial building is exposed to high winds, it’s best to consult a technical representative for the correct attachment recommendations such as fastener size and attachment pattern. Understanding the product you’re installing, preparing the surface of the roof for installation and communicating regularly with the manufacturer can help you select and correctly install underlayments on your commercial building to keep it protected and free from moisture.

Bob Griffiths is product marketing manager at Firestone Building Products Co. Inc., Indianapolis. To learn more, visit www.firestonebpco.comor call (800) 428-4442.