Roof Report

Installation Guideline Tips For Modified Roofing Part I: Asphalt & Adhesive Applied Membranes featured image

Installation Guideline Tips For Modified Roofing Part I: Asphalt & Adhesive Applied Membranes

The birthplace and development of modified roofing began in Europe. Although the original patent has been destroyed, there is evidence that the first designed modified sheet used Whale Oil as a modifier, in Scandinavia in 1929. The launch of modified roofing into the mainstream did not happen until the 1960s throughout Europe. APP was first introduced in Italy and made it to the market in 1967. Modified membranes continued to grow in Europe, and by 1972, it had taken its place in the marketplace.

The North American market saw its first introduction of the domestic produced membrane by WR Grace in 1972, in the US. The Koppers Company in 1975 introduced an APP modified bitumen (KMM). Soprema committed to the modified market in North America, opening its first facility in Drummondville, Québec. Although modifieds entered into the US Market in the early to mid-’70s, Roofing Contractors were hesitant to adapt to the use of the product. It was not until the early to mid-1980s that modified started to gain in popularity among installers.

In Part I of this series, we are going to discuss modified installed with asphalt and cold adhesives. We will cover torch-applied modified systems in Part II. Below are some guidelines and tips from manufacturers, contractors, and my observations over the years to assure a successful and long performing installation.

Deck Preparation

Modified membrane systems can be installed over most types of decks, including structural concrete *, wood decks, lightweight insulating concrete, cementitious structural wood fiber decks, and metal. * Lightweight structural concrete is a high moisture content deck that should not be confused with structural concrete or lightweight insulating concrete. Lightweight structural concrete, with its high moisture content and prolonged drying times, makes it very difficult to determine when a roof can be installed appropriately over these decks. The designer of record must make appropriate design accommodations to address high moisture content encountered in lightweight structural concrete decks to prevent roof failure and other performance deficits.

Regardless of the designed deck, all surfaces that modified bitumens are to be installed on must be smooth, dry, free from contaminants or debris, free from settling or distortion, and any other defects.

On nailable decks, base sheets can be mechanically attached directly to deck following manufactures and local code requirements. On non-nailable decks or over insulation with an appropriate cover board base sheets can be applied in hot asphalt or with a self-adhering base sheet. Concrete decks must be properly primed with manufacturers recommended asphalt primer meeting ASTM D-41 and the primer must be thoroughly dry.

The above recommendations are for new construction or roof replacement with a complete tear-off. We will cover the considerations, evaluations, and procedures for a roof over an existing system left in place in Part III of this series.

Roof Layout

As with most types of roof installations, modified bitumen roof installation starts at the low point of the roof with each successive ply or rolls installed so that no laps are against the flow of water. When the membrane is applied with hot asphalt, manufacturers recommend where roof slope is 1″ (2.54 cm) per foot (30.48 cm) or less, sidelaps will be installed perpendicular to the direction of the roof slope. In conditions where the roof slope exceeds 1″ (2.54 cm) per foot (30.48 cm), rolls should be installed with the sidelaps running parallel to the slope direction. Slopes greater than 1″ (2.54 cm) per foot (30.48 cm) will require “back-nailing” of membrane for SBS hot-applied and self-adhered. Refer to the manufactures specifications for detailed requirements and guidelines.

Endlaps are to be staggered. While different details of endlap staggering are permitted and used by manufacturers and installers, I have always preferred the endlaps staggered three feet apart from each other. In multi-ply applications, membrane sidelaps must also be staggered.

Hot Asphalt Application

Roofing asphalt shall comply with ASTM D-312 Type III for slopes up to 1″ (2.54 cm) per foot (30.48 cm) or Type IV for slopes up to 3″ (7.62cm) per foot (30.48 cm). Asphalt must not be heated to or above the actual flashpoint or held above the finished blowing temperature for more than 4 hours. All ply moppings shall be uniform and free from voids. Bitumen temperature shall be at the Equiviscous Temperature (EVT) ±25°F (±14°C), at the point of application, minimum 425°F(218°C). EVT is defined as the temperature at which asphalt attains the proper viscosity for application (this information is typically found on the product labeling). Adequate heat at the point of application is critical to appropriate adhesion of the membrane plies. Apply asphalt uniformly and evenly without voids; a small bead of asphalt should be visible at all lap areas. Solid moppings require a min. of 25 lbs./100 ft2 (1.2 kg/m²) hot asphalt application

Cold Adhesive Application

SBS modified bitumen adhesive is used to apply SBS modified bitumen membranes, cap sheets, and coated base sheets. Applications rates of required coverage will be found in the manufacturer’s written technical datasheets. Use manufacturers recommended squeegee or spray equipment for adhesive application. Modified adhesives should not be used with SBS modified bitumen membranes designed for torch applications or fiberglass ply sheets.

Membrane application requirements such as endlap and sidelap widths are the same for both hot and cold applications.

Cold Weather Application Recommendations

Roofing systems applied during cold weather poses unique challenges but specific challenges to modified bitumen materials, include maintaining proper temperatures of membranes, adhesives, and asphalt time of application. Cold temperatures cause the sheets to be less pliable, reduce the curing or flash-off rate of adhesives, and reduce the bonding of self-adhesive materials as well as cause mopping asphalts to cool prematurely. Following proper procedures and applying precautions, cold weather applications can be installed as a high-quality result.

  • Adhesives are to be stored at a minimum temperature, typically a minimum of 50°F (10°C). Consult manufactures specific requirements
  • Self-Adhered products at the time of installation, temperatures should be at or above the minimum application temperature specified by the manufacturer. Typically, the minimum temperature range for application is 40-50°F (4-10°C), but you should consult the specific manufacturer for recommendations for material storage and handling during colder weather application.
  • In hot asphalt applications, be sure that all plies are well embedded. Mop-leads should be no more than five feet in front of the roll as a general rule of practice. Using insulated hot equipment will also help prevent premature cooling.

Following these guidelines for SBS membrane roof systems and referring to the manufacturer’s specification manuals, as well as always incorporating internal quality control measures in your installations, will give you a quality and long-lasting roof every time.

In Part II of this series, we cover the Torch Applied APP and SBS membranes, and Part III will include the considerations, evaluations, and procedures for a roof over an existing system left in place.

John Kenney has over 45 years’ experience in the roofing industry. John started his career by working as a roofing apprentice at a family business in the Northeast to operating multiple Top 100 Roofing Contractors. As Chief Operating Officer, John is intimately familiar with all aspects of roofing production, estimating, and operations. During his tenure in the industry, John ran business units associated with delivering great workmanship and unparalleled customer service while ensuring strong net profits for his company prior to joining Cotney Consulting Group. If you would like any further information on this or another subject, you can contact John at