There are well over 500 roofing materials and systems currently in use. The purpose of all of them is to prevent rain water from entering the building structure. The classical roofing materials, such as clay tiles, cedar and asphalt shingles, and metallic panels such as galvanized steel, copper and tin sheets, have all been and are being used successfully for sloping roofs. The bituminous built-up roofing system consists of three or four layers of asphalt (hot melt or emulsion) in conjunction with layers of bitumens saturated or not saturated roofing felts, and a topping of protective gravel. Such a coating was common and for the most part the only roofing system choice for the construction of flat roofs during the past 100 years.
However, technological advances have brought about a new generation of roofing materials consisting of single-ply roofing membranes. These membranes are basically classified into four major groups, as follows:
1. Modified Bitumens: are composite sheets consisting of bitumen, modifiers (APP, SBS) and/or reinforcement such as plastic film, polyester mats, fiberglass, felt or fabrics. The modifying compounds impart flexibility and elasticity while improving cohesive strength and resistance to flow at high temperatures. The reinforcement may be laminated to one surface or embedded within the modified bitumen.
2. Thermoplastics (PVC, ethylene interpolymer): are similar to non-vulcanized elastomers in that there is no cross-linking of the molecules. They can be repeatedly softened when heated and hardened when cooled. PVC membranes may be welded together with heat or solvents and will develop bond strengths which equal or surpass the strength of the base material.
3. Vulcanized Elastomers (EPDM, Neoprene), also referred to as thermosets: are the chemical cross linkage of polymers (chains of molecules) which occurs during the manufacturing process. A distinguishing characteristic is that it can only be bonded to itself during installation by use of an adhesive because once cured, new molecular linkages cannot be formed.
4. Non-Vulcanized Elastomers (chlorinated polyethylene, chlorosulfonated polyethylene, polyisobutylene, acrylonitrite butadiene polymer): are manufactured without any cross-linking between chains of polymer molecules. Although exposure to the elements may naturally cure some of these polymers during their lifetime, all non-vulcanized elastomers can be heat welded during initial installation.
See Roofing Magazine, Single Ply Systems Index, April 1986, pp. 17-42 (D & H Publications, Inc.).
All types of single-ply roofing membranes are applied in one of four ways:
1. Fully adhered to the substrate PA1 2. Loosely laid and ballasted PA1 3. Mechanically fastened PA1 4. Used under insulation board as a protected membrane system.
Typical rolls of these membranes have a width as large as 10 feet and a length cut and rolled to between 30 or 100 feet. During application the membranes are usually lapped two to five inches in the machine direction and up to six inches at the end of the rolls to form a waterproof seam at the overlap. Joining is accomplished by one of the following techniques:
1. Heat, with propane torch or hot air gun (by hand, semi automatic, or self-propelled welding machines)
2. Adhesives, as with solvent, emulsion or solvent based adhesives, double-sided adhesive tapes, or pre-applied adhesive with removable release paper
3. Ultrasonic, microwave, or heat-pressure techniques.