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Material and system description
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.
Polyvinyl Chloride (PVC)
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.
Thermoplastic Olefin (TPO)
- 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
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.
Example of a TPO roof system
- 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 surfacings.
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 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. Please read NRCA's consumer advisory bulletin addressing roofing warranties
for more information. Once the project is complete, be sure the contractor provides
you with a certificate for your records.
Second, the roofing contractor will provide you with a warranty covering his workmanship.
Typically, this will cover installation and related issues. The warranty should
contain what items are covered and what will void them. Many contractors offer one
year or two years of coverage; however, there is no industry standard.