Premium self-adhering underlayment didn’t replace felt but added another level of protection at vulnerable roof areas such as ridge peaks, valleys and edges — particularly roof edges above rain gutters.

Most roofing materials carry warranties that protect homeowners from manufacturing defects and premature failure over the life of the product. But there is no guarantee against the elements themselves. The best — and perhaps only — defense against the forces of nature, regardless of the type of materials used, is a properly installed roof.

Often, however, even a good roof is not enough. High winds, hail, heavy rain, snow loads, ice dams and other naturally occurring hazards can defeat even top-quality roof coverings. Because roofing materials for most homes are designed to shed water or snow from sloped roofs, the problem is usually water backing up or being forced up between the roof covering and the structural roof deck. That’s why smart installers today add an extra layer of protection under typical roof coverings to prevent unseen damage.

Up until the past decade or so, the only other protective barrier a homeowner could install under a roof covering was tar paper or asphalt-impregnated felt. An improvement came from a blend of styrene-butadiene-styrene (SBS) and asphalt that could be made into an SBS-based membrane, a premium self-adhering underlayment with a peelable release film. Premium self-adhering underlayment didn’t replace felt but added another level of protection at vulnerable roof areas such as ridge peaks, valleys and edges — particularly roof edges above rain gutters.

Unlike felt, which will shed water on a pitched slope but is not waterproof (it doesn’t seal against the roof deck, and nail penetrations further reduce its shedding capability), self-adhering underlayment is elastic enough to cling like a second skin and seal effectively around nails, providing a highly water-resistant barrier. When rain or snowmelt is forced up and under roof coverings by strong winds or ice dams in gutters, these membranes stop the water from penetrating to the roof deck, preventing damage to the structure or to the house interior.

What is a Self-adhering Underlayment?

The latest generation of self-adhering underlayments benefit from today’s technologies and offer significant improvements. Typically, these membranes are made of bitumen compounds such as asphalt that have been modified with polymers to be more rubber-like and easier to handle. Better products are made from superior-quality asphalt sources. Most of these underlayments have a peelable release film that simplifies installation (see below).

The blend of SBS and asphalt is something like spaghetti and meatballs mixed with sauce. As illustrated in Figure 1, the butadiene is the “spaghetti,” and the “meatballs” are styrene. Strands of rubbery butadiene run between spheres of styrene, giving the membrane rubberlike properties. The “sauce” is the asphalt, which imparts water-resistance to the membrane. This entire mixture is spread upon a sturdy fiberglass mat, which can be compared to the dinner plate.

The thick, mostly-asphalt membrane resists water yet is easy to apply. The tough fiberglass mat gives strength against rips and tears and makes it easy to handle the membrane. The SBS polymer soaks up asphalt like a sponge, fixes its shape and form, and imparts flexibility and resilience to the membrane. As a result, the membrane is self-sealing around nails. Imagine driving a nail through a rubber ball. The flexible membrane pushes tightly against the nails, blocking moisture from penetrating.

Where to Use

To maximize the life of a roof, premium self-adhering underlayment should be applied directly on the roof deck prior to the installation of other roofing materials such as metal, tile, wood or shingles. This underlayment is not intended for use as the primary roof covering.

In areas where the average daily temperature in January is 25 degrees F (-4 degrees C) or less, the use of a self-adhering modified bitumen sheet is recommended (International Residential Code, Section R905.2.7.1 Ice Protection). This creates an effective barrier against water intrusion typically caused by snow, ice and water buildup, melting and freezing, and expansion and contraction of shingles and other roof coverings.

Ice dams in rain gutters along the eaves of homes are difficult to prevent, especially in climates where freezing and thawing occur repeatedly during winter months. Figure 2 illustrates an ice dam on the eave of a residential roof.

While premium self-adhering underlayment is essential in cold climates, it is also being widely installed by contractors and homeowners in practically every region of the country. Wind-blown rain and water intrusion resulting from leaf- and debris-clogged gutters can plague homeowners year-round in any climate. All of these conditions contribute to the failure of roofing materials to fully protect a home against leaks.

Even worse, any water that gets under the roof covering can cause serious damage to both the roof deck and the house structure below it, as well as to the interior of the home itself. Premium self-adhering underlayment is the last line of defense against leaks “when nature prevails and shingles fail.” It provides an additional barrier against water intrusion and damage due to ice and snow dams, water “wicking” and wind-blown rain.

Even in warmer climates where ice dams are rare, there are countless everyday uses for premium self-adhering underlayment. It can be used as a flashing material for edges and valleys of roofs. Chimneys, skylights and vents require special treatment and premium self-adhering underlayment is ideal for guarding against leaks around these vulnerable areas. Figure 3 shows typical areas that can benefit from the installation of a premium, self-adhering underlayment.

For metal roofing systems, traditional underlayments have not held up well under the heat. Some manufacturers supply high-temperature formulations of self-adhering underlayment, which have a high softening point and can withstand extreme temperatures underneath a metal roofing system.

How is Premium Self-adhering Underlayment Installed?

As always, you should check with the manufacturer’s guidelines when installing any product. With Tarco’s LeakBarrier Ice and Water Armor, the first step is to determine the areas to be covered. The International Residential Code recommends extending coverage from the eave’s edge to a point at least 24 inches (610 millimeters) inside the exterior wall line of the building.

Rolls typically are supplied in sizes of 1, 1 1/2 or 2 squares. Before installing the underlayment, the roof deck should be clean, dry, and free of dust, oil and grease. Do not install this product directly on old roof coverings. Once the materials are purchased and the roof deck is prepared, installation is easy. The self-adhesive underlayment backing is covered by a two-piece release film that makes handling and positioning a snap. No other adhesives or heat are needed. For re-roofing applications, all old roofing and other loose materials must be removed. Apply when ambient temperatures are 40 degrees F (5 degrees C) or higher.

Step 1: Roll out a sufficient length of premium self-adhering underlayment and cut it to fit the roof edge or area to be covered.

Step 2: Position this strip on the roof deck with one end of the release film facing up. Peel off 1 to 2 feet of film, exposing the self-stick backing.

Step 3: Align the membrane along the gutter edge of the roof deck. Press down to adhere the membrane to the deck and continue along the edge, peeling away the protective backing as you go. Side laps must be a minimum of 3 inches and end laps a minimum of 6 inches. (See Figure 4.)

Better Roofs Bring Peace of Mind

Premium self-adhering underlayment is a relatively new product for residential roofing. Its modified-bitumen technology and manufacturing methods are only now becoming standardized and widely adopted in the roofing industry. As a result of its increased availability, builders, contractors and homeowners are increasingly installing this added layer of protection for peace of mind. Homeowners can protect their homes by avoiding roof leaks, property damage and emergency repair calls. Contractors can protect their reputation with higher-quality work, fewer call backs and satisfied customers.