01 May 1999
(5) Familiarity with the System and Site. EPDM is well known by many commercial roofing
contractors. Only manufacturer-approved contractors should install these systems. All membrane
components should be from a single source. Since primers and adhesives use toxic, flammable
solvents, avoid fume intake into the building's air handling system.
(6) Life Expectancy. EPDM systems typically last 15 or more years although some have had
seam and flashing problems much sooner. Wind erosion of ballast and shrinkage problems occur on
(7) Costs. EPDM systems are very cost effective on both initial and life cycle bases.
Ballasted systems using MEPS (molded, expanded polystyrene) insulation are one of the most cost-
effective membrane roof systems, especially on roofs where there are few penetrations. Fire retarded
(FR) EPDM is more expensive and is used in unballasted systems only. (The rock ballast protects the
non-FR EPDM membrane against external fire exposure.)
6-2. BUILDING ELEMENTS.
a. Slope. A minimum slope of 2% (1/4 in./ft.) is required.
b. Low-Sloped Roofs. Moisture and vegetation attack can occur where water ponds and root
growth occurs. Laps joined together with self-adhesive tape are more resistant to moisture than seams
made with liquid neoprene or butyl adhesives.
c. Steep Roofs. At slopes above 16.7% (2 in./ft.), ballasting is no longer feasible. Mechanically
attached and fully adhered systems have been used on barrel vault and folded plate roofs.
Mechanically attached systems should not be used on steep roofs in windy areas.
d. Structural Considerations. Ballasted EPDM systems are heavy with ballast at 49-108 kg/m
(10-22 psf) depending upon expected wind force. Mechanically fastened membranes weigh
approximately 5-10 kg/m2 (1-2 psf). They are subject to wind flutter and increased fastener density is
required at corners and perimeters. The heavy EPDM rolls require appropriate hoisting equipment.
Dunnage should be used to distribute the weight so that the structure is not overloaded.
e. Expansion Joints, Seismic Joints and Area Dividers. Joints should be located at high points
where practicable, and placed on curbs above the water line. Expansion joints should be provided only
at each expansion joint in the structure. Structures need expansion joints at intervals not over 60 m
(200 ft.) in length or width. If a structure does not contain enough expansion joints, it is inappropriate to
solve that problem by just adding expansion joints to the roof system. Joints should also be used at
changes in deck direction or material. Because of the flexibility of EPDM, the membrane material
(supported by flexible foam) is sometimes run directly over the curbs of the joint without a change of
material. Raised joints should be used rather than flush joints at water level.
Re-entrant Corners. EPDM systems require no special treatment.
g. Roof Access. Roof access is essential to maintenance and inspection functions; however,
unauthorized access should be controlled (provided that it does not interfere with means of egress in
an emergency). Heavily trafficked areas should use either pavers installed over protective matting or
h. Roof Venting. Roof vents have been proven to be of no value in drying wet materials and their
efficacy for pressure relief is questionable. However, pressure-reducing vents have been used in
single- ply systems to reduce under-membrane uplift pressure.