EPDM Introduction

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EPDM Introduction

Due to the complexities involved in non-bituminous flexible membranes, “generic” application specifications and details are not possible. This section of the manual contains both an overview of the products, their composition, usage, and design considerations, and the accepted membrane manufacturer's written submissions. In all cases, the membrane manufacturer should be contacted for further recommendations and details.

In order to formulate materials to satisfy the requirements of a roof membrane, the manufacturer must ensure:

  • Strict Quality Control
  • Proper Mix of Ingredients
  • Consistency of Batches
  • Minimum Physical Properties are Obtained

The chemical formulations of specific flexible membranes can be complex, but the end product can generally be defined as either a THERMOSET (Section 6.1) or THERMOPLASTIC (Section 6.2).

Thermoset is defined as a material that solidifies or “sets” irreversibly when heated (vulcanized). This property is usually associated with cross-linking of the molecules induced by heat or radiation. Once the material is cured, it can only be bonded to itself by adhesives; new molecular linkages cannot form. Some thermosets are not cured during manufacture (ie. EPDM flashings) and are intended to cure over time after they have been installed. This allows the material to cure into the specific shape required for the roofing application.

The generic membrane types defined as cured thermosets include:

  • EPDM (Ethylene Propylene Diene Monomers)
  • Neoprene (Chloroprene Rubber)
  • CPE+ (Chlorinated Polyethylene)

Uncured thermoset membranes include:

  • CSPE (Chlorosulphonated Polyethylene)
  • CPE+ (Chlorinated Polyethylene)
  • PIB (Polyisobutylene)
  • NBP (Nitrile Alloy)

+CPE's may be formulated to be used as either a cured or uncured membrane.


EPDM is a thermoset, synthetic rubber membrane formulated from ethylene, propylene, and a small amount of diene monomer. Although most commonly available as a cured sheet, EPDM can be formulated as an uncured membrane for specific purposes (i.e., flashings).

EPDM roof systems are single-ply membranes available in thicknesses ranging from a nominal 1.1 mm (0.045") to 1.5 mm (0.060") and are usually black or white in colour. The membrane may be applied loose-laid and ballasted, mechanically-fastened, or fully-adhered. Seams are joined with contact splicing cement or seaming tape (or a combination of both), and are sometimes caulked (see manufacturer's requirements).

EPDM membranes should conform to CGSB 37-GP-52M 1984, “Roofing and Waterproofing Membrane, Sheet Applied, Elastomeric” which lists two types of membrane, according to manufacture:

  • Type 1
  • Type 2

and two classes, according to end use:

  • Class A
  • Class B

This standard covers requirements such as “thickness, tensile strength, breaking strength, lap joint strength, elongation, tensile set, low temperature flexibility, water absorption, dimensional stability after water absorption, heat aging, ozone resistance, resistance to accelerated weathering, dynamic impact test, tear resistance, and tearing strength.”

EPDM Roof Systems

Definition and Terms