St. Louis Commercial and Residential
Modified Bitumen Roofing System

low slope modified bitumen roofing system options

Photo: GAF Low Slope Options Brochure

For roof repairs with flat areas that are hard to access, a self-adhering modified bitumen system has increasingly become more popular in the low-slope commercial roofing market. But, this type of system requires particular attention during installation to ensure that it will be watertight.

Weather is one of the most critical factors for self-adhering modified bitumen roofing systems. For most roofing systems 40 degrees Fahrenheit or 4 degrees Celsius and rising are the most common temperatures. However, self-adhering roofs require 50 degrees Fahrenheit or 10 degrees Celsius or above and rising through the day. The bond of self-adhering membranes will not be at full strength immediately; it will require time and heat to gain full strength. In addition to the surrounding climate, the substrate and temperature of the materials is also critical.

Materials stored on the roof are often exposed to very cool night time temperatures. These materials will be allowed to warm and relax for proper installation. Just as cool weather can have a negative effect on bond strength, extremely high temperatures can have a detrimental effect on self-adhering roofing systems. The ideal temperature range for self-adhering systems is between 50 degrees Fahrenheit or 10 degrees Celsius and 100 degrees Fahrenheit or 38 degrees Celsius. The nature of the self-adhering compound is softer than conventional flat roof systems. So in extreme heat, the sheets will be softer and will require special protection, especially in traffic areas.

Since extreme St. Louis temperatures can affect the application of self-adhering modified bitumen roofing systems, if there is ice, snow, moisture or dew present; a delay in installing the application will be likely because it’s crucial that the substrate is clean, dry and free of dust or other inhibitors that will prevent proper adhesion.

Most self-adhering roofs will have one or more layers of roof insulation. Cover boards are recommended for adhesion over self-adhering modified bitumen roofing systems. Acceptable cover boards have a powder or residue on their surface. The surfaces of the boards are lightly primed with an asphaltic or coat primer to improve the bonding between the base sheet and cover boards.

For laps, flashing, or wherever a self-adhering membrane touches a mineral surface, a uniform application from 1/8 to ¼ of flashing bond to the end laps to ensure adhesion is needed. T-joints are critical for self-adhering systems. Flashing heights should not exceed 24 inches.

GAF bitumen self-adhered roofing system

Photo: GAF Self-Adhered Technologies

It will be necessary to install insulation board if the flashing substrate is a block or plywood with flashing in a cold process adhesive. A heavy weighted roller working outward from the center of the sheet is rolled over the area to prevent voids. A hand-held hot air welding gun is used to warm the lap areas and improve adhesion especially when temperatures during installation are cooler.

Self-adhering modified bitumen roof systems are here to stay. When installed properly, these roofing systems provide building owners with long-term, leak-free buildings. It’s also a complementary fit for customers who want an environmentally sensitive application.

Ridge Top Exteriors located in Florissant, MO has extensive experience in the commercial and industrial roofing market in St. Louis, all of St. Louis County and nearby Illinois cities. The roof on your business is as important as the one on your home.

Browse our site and give us a call to talk to one of our residential and commercial flat roofing specialists to plan a course of action that will best suit your needs.