Thermoplastic materials are distinguished from thermoset materials in that there is no chemical crosslinking. These membranes can be repeatedly softened by heating or hardened when cooled. Because of the materials' chemical nature, thermoplastic membranes typically are seamed by heat welding with hot air or solvent welding.
There are five common subcategories of thermoplastic roof membranes.
Polyvinyl Chloride (PVC)
PVC Alloys or Compounded Thermoplastics
Copolymer Alloy (CPA)
Ethylene Interpolymer (EIP)
Nitrile Alloys (NBP)
Tripolymer Alloy (TPA)
Thermoplastic Olefin (TPO)
Chlorinated Polyethylene (CPE)
The most common thermoplastic roof membranes are PVC and TPO. The following provides general descriptions of these two systems.
PVC sheets are produced by calendaring, spread coating or extruding, and typically are reinforced with polyester or glass-fiber mats or scrim. PVC sheets contain plasticizers and stabilizers, as well as other additives to impart flexibility and achieve other desired physical properties. Some membranes are available with nonwoven fleece backing adhered to the underside of a sheet.
Sheet widths range from 6 feet to 12 feet wide.
Sheets are typically 45 mils to 90 mils thick.
Seams are sealed by heat or chemical welding.
PVC membranes are produced in numerous colors, though gray and white are the most common.
TPO membranes are produced by calendering with lamination, extrusion with lamination, or extrusion-coating techniques. TPO sheets are a blend of polypropylene and ethylene propylene polymers and usually are reinforced with polyester. TPO sheets contain colorant, flame retardants, UV absorbers and other proprietary substances to achieve desired physical properties.
Sheet widths range from 6 feet to 12 feet wide
Sheets are typically 40 mils to 100 mils thick
Seams are sealed by heat welded with hot air
TPO membranes commonly are white
PVC and TPO roof membranes can be installed fully adhered mechanically attached or ballasted. Most PVC and TPO membranes do not receive surfacing.
NRCA does not make any recommendations about which TP product or manufacturer to use; however, NRCA does recommend that TP products meet standards established by ASTM International.
ASTM D4434, "Standard Specification for Poly(Vinyl Chloride) Sheet Roofing"
ASTM D6878, "Standard Specification for Thermoplastic Polyolefin Based Sheet Roofing"
When purchasing a new roof system, there will be two warranties to consider. First, there will be the manufacturer's warranty. In general, these warranties cover defects in the manufacture of the roof membrane, and vary greatly depending up the specific material and products chosen. The Second is the Workmanship. At DC Contractors, we provide a 3 year warranty covering all workmanship unless otherwise specified for your particular project.
Thermoset membranes incorporate principal polymers that are chemically cross linked or vulcanized. Membranes that are vulcanized also may be referred to as "cured." One characteristic of true thermoset polymers is once they are cured, they only can be bonded to similar materials with adhesives.
There are five common subcategories of thermoset roof membranes:
Ethylene propylene diene terpolymer (EPDM)
Chlorosulfonated polyethylene (CSPE)
The most common thermoset roof membrane is EPDM. EPDM principally is composed of two compounds, ethylene and propylene, that are derived from oil and natural gas. The following are some characteristics of EPDM roof membranes:
Sheet widths range from 7.5 feet to 50 feet wide.
Sheets are typically 45 mils and 60 mils thick.
Seams are sealed using liquid adhesives or special formulated tape.
The membranes commonly are black, but white is available.
EPDM roof membranes can be installed fully adhered mechanically attached (using batten bars) or ballasted. Most EPDM membranes do not receive surfacing.
EPDM and polymer-modified bitumen membranes often are confused by consumers because of colloquialisms used by roofing contractors. Contractors commonly call both of these membranes "rubber" roofs. However, in most cases, when contractors specify rubber roofs, they are referring to EPDM.
NRCA does not make any recommendations about which TS product or manufacturer to use; however, NRCA does recommend that TS products meet standards established by ASTM International.
ASTM D4637, "Standard Specification for EPDM Sheet Used in Single Ply Roof Membrane"
ASTM D4811, "Standard Specification for Nonvulcanized (Uncured) Rubber Sheet Used as Roof Flashing"
ASTM D7067, "Standard Specification for Reinforced White PIB Sheet Used in Roofing Membrane"
When purchasing a new roof system, there will be two warranties to consider. First, there will be the manufacturer's warranty. In general, these warranties cover defects in the manufacture of the roof membrane, and vary greatly depending up the specific material and products chosen. The Second is the workmanship. At DC Contractors, we provide a 3 year warranty covering all workmanship unless otherwise specified for your particular project.