What’s new in residential metal roof underlayments?
A roofing underlayment is a membrane that prevents water penetration. Compared to exterior roof-covering materials like metal or shingles, underlayment is the secondary barrier to moisture penetration. It is the one piece of a roofing system that is expressly designed to be waterproof. Without a correctly installed, fully functional underlayment, water from wind-driven rain or ice dams can infiltrate under a house’s shingles and severely damage the roof, or even worse, the inside of a home.
About 30 years ago, they were simply temporary home protection against the elements with one-size-fits-all usability. Today underlayments are more multi-dimensional and come in multi-varieties, which help to produce more durable, longer-lasting, residential metal roofs.
Taking the heat
With the popularity and advances in metal roofing systems being applied to residential structures, be aware of the unique heat-generating properties created by these systems. High heat can easily break down an underlayment, which can lead to water damage and future call-backs to the job site for repair.
“Proper ventilation is the first priority,” stresses David Delcoma, product marketing manager,
MFM Building Products Corp., Coshocton, Ohio, “but when it comes to protecting the roof deck from any moisture damage, a high temperature-rated underlayment is required. In terms of a self-adhering underlayment, the asphalt adhesive system must be able to withstand temperatures as high as 250 F. If it is not rated for under metal roofing, the adhesive system will break down, and the underlayment will not be properly adhered to the roof deck and lose its waterproofing capabilities.”
New, high temperature-rated, self-adhering underlayments are available designed specifically for metal roofing systems. MFM Building Products’ Ultra HT Wind & Water Seal has an extremely tough and durable cross-laminated polymer film backed with a specialized adhesive system to withstand extreme temperatures. It helps fully protect the roof structure in the event of water or moisture intrusion under the metal roofing system. It’s tested to ASTM D 1970 and has Florida Building Code approval.
Fabric and film
Self-adhesive metal roof underlayments with fabric and film surfacing are recent innovations aiding residential metal roofs. Self-adhesive metal roof underlayments consist of a rubberbased
(SBS polymer) asphaltic adhesive formulation, which has a self-sealing characteristic. This feature greatly enhances the watertightness of the membrane.
Fabrics, typically based on polyester, provide a good walkable surface enabling safe installation. Additionally, they allow the membrane to be left exposed for extended time periods, up to six months. They also tend to be non-abrasive, an added benefit when used in conjunction with metal panels. “Self-adhesive metal underlayments do not require the use of a propane torch or hot kettle or cold-process adhesive to install,” says Steve Ratcliff, president of Tarco, Little Rock, Ark. “The adhesive compound on these membranes is protected by a siliconized release film, whereby all that is required at the time of installation is for one to remove the release film and apply the exposed side to the roof substrate. Self-adhesive compounds require ambient heat such as sunlight, as well as pressure to activate. So, once the membrane is installed at 40 F or above, the sheet will adhere to substrate when these conditions occur.”
The synthetics
Synthetic underlayments are growing in usage on residential metal roofs. A higher-end product that can hold up well to the abuse residential roofs face, synthetics can even be safer for roofers to work with. They are commonly used in other parts of the world, such as Europe and Asia, where oil prices are significantly higher and roofs are often expected to last a minimum of 50 years. Synthetic underlayments can be made of various polymers and can be single or multiple layers for a variety of purposes from strength to a safe-gripping walking surface.
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“There is a tendency toward premiumunderlayment products-referred to by Atlas as ‘engineered underlayment’-synthetic underlayment products and more quality underlayment products in general, for several reasons,” says Brian Short, business unit manager for Atlanta-based Atlas Roofing Corp.’s business division. “First, to keep the roof deck protected while it is open, as well as providing additional protection over the long term as part of a complete roof system. It is an additional layer of protection should any penetration of the surface take place at any time during the life of the roof.”
However, Ratcliff says they are not asphaltbased and usually do not possess self-sealing characteristics. “They also tend to be thinner than asphalt-based roofing underlayments and do not provide the flexibility in installation method as traditional roofing membranes; synthetics are typically installed by mechanical attachment,” he says. Delcoma believes that while synthetics can be less expensive than self-adhering underlayments, they do not provide whole roof protection in the event of a roofing failure as self-adhering products can.
Glass fibers and exposure
During Atlas Roofing’s 2013 road trip, in addition to allowing contractors to actually walk on steepsloped displays of its underlayment to see how strong the traction is, it showed off a new high-quality roofing underlayment with glass fibers. Its product, Gorilla Guard EVERFELT, is a high-performance roof underlayment for steep-slope roofs. It out-performs typical organic felt because of the glass that saves time and labor costs. It lays flatter on decks in wet conditions and is highly resistant to wrinkling. It resists tear away from fasteners when walked on or in strong wind when properly installed.
Extended exposure offers roofing contractors more flexibility in planning residential roof underlayment installation. Vancouver, British Columbia- based InterWrap’s CPSU-30 underlayment provides roofers the ability to dry-in construction projects, or tear off re-roof projects and cover the roof deck with it as a temporary waterproof barrier until the primary roofing can be installed. This enables roofers to effectively manage multiple projects without tarps or rushing the project to avoid bad weather. This eliminates blow-offs and callbacks. Its tear strength, unique lap seal system and high-strength durable adhesive make it suitable for heavy traffic applications such as installing under metal residential roofs.
Atlas Roofing’s Summit Synthetic underlayment offers longer exposure time, allowing roofing contractors to more efficiently plan their work schedule without the concern of weather. The unique woven material is considered a non-breathable underlayment allowing the product to protect the roof deck for a longer period of time. “The UV coating throughout the product enables it to stand up to the harshest UV rays, which is why we offer a six-month exposure rating,” Short says.
Installation innovations
Residential metal roof underlayment manufacturers are finding innovative ways to more efficiently install their products. Cambridge, Mass.-based WR Grace and Co. has a unique Ripcord feature that makes Grace Ice & Water Shield easier to apply by giving the applicator a split release on demand. Faster application of the membrane in the straightaways, as well as ease of membrane positioning in detailed areas (valleys, around dormers, etc.), are just some of the benefits. “For valley and ridge application, peel the release liner, center the sheet over the valley or ridge, drape, and press it in place,” says David Baur, WR Grace and Co. product manager of residential waterproofing. “Work from the center of the valley or ridge outward in each direction and start at the low point and work up the roof.”
Stay updated
A great way to stay abreast of new product innovations in residential metal roofing underlayments is to be familiar with their manufacturers’ approved substrates. This can be easily done by contacting the underlayment manufacturers directly or visiting their website and learning more about their products.
