01 May 1999
ELASTOMERIC (EPDM) ROOFING SYSTEMS
REFERENCE CEGS 07530
6-1. ELASTOMERIC SYSTEMS.
a. Overview. By definition an elastomer is a material that can be stretched to at least twice its
original length and when the deforming force is removed, will return to approximately its original
dimensions. These materials are sometimes referred to as rubber or vulcanized thermosets. Of the
elastomers used in membrane roofing, EPDM (originally ethylene propylene-diene monomer, now
terpolymer) (ASTM D4637) rubber is by far the most popular today. Others that have occasional use
include neoprene (chloroprene), butyl (IIR) and polyepichlorohydrin (ECO). These elastomeric
membranes are true single-ply systems. The polymer is factory compounded with carbon black, other
fillers, oils, processing aids, fire retardants, and curatives and formed into sheets. Commonly, roll
widths are further processed into large tarpaulins and then vulcanized. EPDM is neither remeltable nor
recyclable. In the field the giant rolls are unrolled over a suitable substrate, seamed to adjacent
sheets, and flashed. Because of high elasticity, EPDM roofing can be applied as a loose-laid or
partially- attached system in addition to being fully adhered. The carbon black provides reinforcement
for the polymer as well as UV protection. EPDM membranes may be unreinforced or have internal
scrim reinforcement. (Scrim reinforcement is used in mechanically fastened systems.) Typical
product thicknesses are 1.1 mm (0.045 in.), 1.5 mm (0.060 in.), and 2.2 mm (0.090 in.). Black is the
most durable color but white is available for special purposes. Fire retarded sheets are also available.
b. General. While EPDM sheets are waterproof, seams may be moisture sensitive. The roof
must have positive drainage; seams should not buck water.
(1) Installation. Key steps in installation include hoisting the heavy rolls to the roof, unrolling,
allowing the membrane to relax (to relieve winding stresses), and then:
(a) Attaching it to the substrate with adhesive followed by seaming sheets together and
flashing the system, or . . .
(b) Mechanically attaching the membrane to the substrate followed by seaming and
flashing, or . . .
(c) Seaming the loose sheets together securing them at the perimeter and at
penetrations, flashing the system, and then ballasting the loose-laid membrane to resist wind forces.
(d) Application. Application instructions are provided in industry literature. Field quality
assurance should verify that they are followed.
(2) Substrates. Suitable substrates for adhered systems include solvent resistant thermal
insulation boards (i.e., not polystyrenes) and most flat decks. Polystyrene insulation is used for loose-
(3) Climate/Weather. During installation, rubber sheets require clean, dry substrates and
above freezing temperatures. Excessive wind will make application difficult. Loose-laid membranes
require temporary ballast to prevent blow-off until all ballast is placed. Ballasting may be done in
inclement weather. Black EPDM is very hot to work on under the summer's sun.
(4) Logistics. EPDM rolls tend to be wide and heavy; in some cases they weigh a ton or
more. Proper hoisting equipment is essential, and once hoisted the rolls should be supported so as to
avoid localized overloading of the deck. Adhesives may be flammable and the quantity stored on the
roof should be limited to the day's needs.