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 simliar 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 surfacings.
Example of a fully adhered EPDM roof system
Example of a ballasted EPDM roof system
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 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
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.