Protecting the Roof Investment: Underlayment Strategies for Cedar, Metal, and Asphalt

When designing a home’s roof, it’s critical to not only carefully consider what material the roof is made of but how that material is working as a system with the products underneath to provide protection and ensure proper movement of air and moisture. Roofing systems that don’t properly manage air and water can experience rot, decay, and premature failure.

No matter the material, protecting the roof investment comes down to understanding the different layers of the entire roof assembly, from the shingles to the attic insulation. Consider these underlayment strategies from Benjamin Obdyke, a leading supplier of high-performance building envelope products, to protect the longevity of a wood, metal, or asphalt roof.

How to Better Protect Cedar Roofs

A durable cedar roof starts with well-manufactured cedar. It’s tempting to seek out the cheapest alternatives, but buying off-grade cedar can lead to rapid deterioration. Organizations like the Cedar Shake & Shingle Bureau offer recommendations and guidelines for evaluating grading information and inspection details.

From there, make sure you’re specifying systems that don’t contribute to early failure. Cedar shingles need an air space underneath to ensure trapped moisture can move and escape; cedar that is installed directly to the ice and water shield is likely to trap moisture, particularly on the underside, leading to cupping and warping. By keeping cedar shingles off the underlayment and creating an air space, you can dramatically reduce the moisture underneath and help ensure the moisture content of the shingle is the same on the back side as it is on the face.

The ideal system underneath a cedar shingle roof combines VaporDry SA roofing membrane with Cedar Breather roof ventilation mat over top. VaporDry SA is one of the few self-adhered, vapor-permeable roofing membranes, allowing moisture from the attic to migrate, increasing drying potential of the roof deck. Then, Cedar Breather’s 3D design provides an airflow space between the membrane and the wood shingles, allowing for drainage and drying; it is most effective when used with a ridge vent such as Rapid Ridge 7. Cedar Breather also eliminates the need for furring strips.

How to Better Protect Metal Roofs

Metal roof panels are impermeable, so water vapor will not move through them. This creates a concern about condensation building up on the underside of the metal. Combine this with the outside air against a cold roof and, over time, corrosion may develop. So, just like cedar, metal roofs need to be ventilated underneath to ensure proper airflow and drying.

As a best-case approach, the roofing system below the metal roof will include spray foam insulation in the rafters, VaporDry SA roofing membrane on top of the sheathing, and then Cedar Breather. When combined with a ridge vent, this design will create convective airflow to help reduce the risk of high moisture concentration. The metal roofing can be installed directly to the VaporDry SA membrane, but including Cedar Breather will allow for optimal drying.

Along with more drying potential, Cedar Breather decouples the metal from the roof sheathing, helping to reduce noise transfer from rain and hail. Cedar Breather also can help address oil canning—in which the standing seam metal begins to wave or ripple over long spans of uneven roof framing—by creating a cushion and leveling out imperfections in the roof.

When installing a Cedar Breather system under metal roofing, ensure that the roofing fasteners you use can accommodate the added thickness of the Cedar Breather.

How to Better Protect Asphalt Roofs

Asphalt shingles don’t benefit from airflow as much as wood and metal, so they are often installed directly to the underlayment, with ice and water shield used at the eaves and valleys. The 100% continuous acrylic adhesive of VaporDry SA roofing underlayment is the ideal option for this application: It offers higher performance than asphalt adhesives, which are greatly affected by temperature, and provides sealing around fasteners to create a full air control layer. VaporDry SA also can provide temporary protection in case of shingle blowoff or damage. Also keep in mind that ice and water shield should only be used at eaves and valleys, so it’s typically paired with felt paper; VaporDry SA, on the other hand, can be used across the entire roof, thereby eliminating the need for multiple products while also providing greater resistance to tearing during installation.

For more information on Benjamin Obdyke products, visit www.benjaminobdyke.com.

About Benjamin Obdyke

Since 1868, Benjamin Obdyke has been helping architects, builders, and contractors in the United States and Canada Build Better™ by developing and adding new advances to its product line. Benjamin Obdyke develops, sources, markets, and sells proprietary roof and wall products that improve the building envelope and the performance of other building materials for the new construction, repair, and remodel markets. Innovations from Benjamin Obdyke, such as the first roofing ridge vent on a roll, the first wood roofing underlayment, and the first rolled product to provide drainage and air flow in rainscreen wall assemblies, have helped shape today’s building practices. Headquartered in Horsham, Pa., Benjamin Obdyke partners with a network of distributors, dealers, buying groups, and cooperatives to reach building professionals in the United States and Canada. For more information, visit https://benjaminobdyke.com.

Contact:

Katy Tomasulo – Media Contact – ktomasulo@truedigitalcom.com

Source: Benjamin Obdyke Incorporated