01 May 1999
(1) EPDM Membrane. The most common membrane used in ballasted systems is 1.1 mm
(0.045 in.) black, unreinforced EPDM. Reinforced EPDM with a minimum of 0.38 mm (0.015 in.) of
polymer coating over the scrim is required for all mechanically fastened systems. Thicker membranes
are more durable and less likely to wrinkle when installed in fully adhered systems. ASTM D4637
covers EPDM sheeting material and ASTM D4811, nonvulcanized rubber used in some flashing
(2) Surfacing. EPDM membranes have excellent weather resistance and need no surfacing.
While white EPDM may be available the durability is considered inferior to that of black. It is more cost
effective to add additional thermal insulation to a black membrane system to conserve energy than to
rely on white rubber to reduce solar loads or to attempt to apply reflective coatings to black rubber.
When ballasted, EPDM rubber needs no fire retardant. Expensive fire retarded (FR) EPDM is
necessary to meet most fire requirements for unballasted applications.
m. Penetrations and Flashings. Flashing, perimeter securement, and detailing of EPDM systems
is critical. Construction detail plates are available from the NRCA, SMACNA, and individual
manufacturers. Pipe flashings are handled by using molded boots that are clamped to the penetration
and bonded to the membrane. Pitch pockets are filled with a compatible, curing pourable sealer (non-
n. Historical Roof Restoration. EPDM membranes may be very useful in historical renovation.
Adhered and mechanically fastened systems are light in weight and very versatile.
o. Aesthetics. In typical low-slope applications aesthetics is rarely of concern. Ballast and pavers
are relatively attractive with some color choices available. Black membranes are acceptable but not
overly pleasing. EPDM membranes can be converted into PMR's, or plaza decks, when combined
with extruded polystyrene, filter fabric, and ballast.
p. Gaps, Flashings, Joints, and Sealants
(1) Gaps. Spaces in the substrate wider than 6 mm (1/4 in.) should be filled in with thermal
insulation by inserting pieces of insulation or replacing broken boards. Gaps in uninsulated nailable
decks are bridged with sheets of galvanized steel.
(2) Flashings and Termination Bars. Flashings for EPDM systems do not require cant strips
to reduce the angle at the base of the wall or curb. Termination bars are required to secure the
flashing membrane at the top of the wall or curb. Manufacturer details, modified to specific job
conditions, should be followed. Perimeter restraint is necessary to minimize the potential for
(3) Sealants. Sealants are used primarily within seams and at exposed lap edges in
adhesive systems, and to seal the interface between termination bars and vertical walls.
q. Drainage, Valley and Intersection Details.
(1) Drains. Roof drains should be sized to meet the National Plumbing Code. Secondary
(overflow) drains or scuppers should be designed in accordance with ANSI/ASCE 7-95. Over-the-
eaves drainage is acceptable in areas where ice dams are not expected. Interior drains avoid drain
and leader freeze-up. Primary roof drains should be recessed below the roof line by using deck sumps
(uninsulated decks) or by creating a sump out of roof insulation in order to properly collect water.
(2) Drain Clamps. The roof membrane is bonded to the drain bowl using water cut-off mastic
where the clamping ring compresses the membrane.
(3) Ballast Retention. Ballast retainers may be installed around drains. Special perforated
metal ballast retainers are used to retain ballast at eaves and scuppers.