Skip to Main Navigation Skip to Content

Under One Roof

Canadian Roofing Reference Manual

7.2 Thermoset Membranes

Thermoset single ply membranes include:

  • Ethylene Propylene Diene-Monomer (EPDM)
  • Neoprene
  • Polyiso Butylene (PIB)
  • CSPE (Chlorosulphanated Polyethylene) [also called by its trade name – HypalonTM

Thermoset membranes are generally made of synthetic rubber (elastomers), formed in wide sheets and applied as single layer systems. They are called “thermoset” because the material solidifies, or “sets” when heated. This process is called vulcanization. Once the material has been cured, it cannot be re-melted or reshaped as can a thermoplastic material. For this reason, thermoset material cannot be heat welded, but must be bonded to itself using adhesive or tapes. In the case of EPDM, the curing takes place when it is being manufactured, before it arrives to the site. In some cases, as with CSPE (Hypalon™) or uncured EPDM flashing, the material arrives to the site uncured or semi-cured. In this state Hypalon@trade; is heat weldable and the curing occurs over time with exposure to the heat of the sun and air. Once fully cured, you can no longer heat weld the material.

The curing process produces a chemical change in the material, known in scientific terms as the cross-linking of molecules. It is this process that gives the material its rubber like qualities. Elastomeric membranes, such as EPDM, can be stretched repeatedly and they will recover their original shape.

Thermoset membranes come in a variety of thicknesses and colours and can be either internally reinforced or non-reinforced and may have factory bonded facings or adhesives such as fleece backing (fleeceback), pressure sensitive adhesive (self-adhesive) or velcro backing. They are used in loosele-laid, fully adhered, and mechanically fastened systems.

They can also be used for waterproofing foundation walls, tunnels, basements, and other underground structures or as reservoir linings.

The most widely used thermoset single ply roofing membrane is EPDM. EPDM roof membrane is typically available in either black or white although some specialized products may be available in other colours. Black EPDM sheets are the most common, as carbon black is a key ingredient of thermoset membranes and the carbon black gives the membrane the properties of UV resistance (weatherability) and strength.

Thermoset membranes are available in various thicknesses typically ranging from 1.1 mm (45 mils) up to 2.3 mm (90 mils). When speaking of thermoset membranes, it is common to measure thickness in mil (thousandths of an inch). By example, 60 mils would be 60/1000 in or 1.5 mm. Thermoset membranes can be both reinforced and non-reinforced. Normally, the non-reinforced material is used in loose-laid and ballasted systems. Thermoset membranes are also available with fleece backing for adhered applications, factory applied bonding adhesive for pressure-sensitive (self- adhered) applications, and with a special fleece backing intended for connection to velcro faced insulation panels. Non-reinforced thermoset sheets also come in a variety of sizes that typically range from 3 m to 15 m (10 ft to 50 ft) in width and up to 60 m (200 ft) in length.

Despite its excellent weather resistance, thermoset membranes are vulnerable to chemical attack from oils, fats and can degrade when in contact with asphalt or tar.