Roofing Systems

Single-Ply Membrane Systems

Single-ply membrane roofing systems account for just over 40% of all new low-slope construction and about 32% of re-roofing. Single-ply membranes are factory-manufactured roof coverings compared to BUR membrane systems that are constructed on the roof from bitumen and reinforcing fabric materials. Single-ply membranes are generally categorized as either thermo-plastic or thermo-set, and are usually identified by their chemical acronyms, such as ethylene propylene diene monomer (EPDM) or polyvinyl chloride (PVC). The membranes may contain reinforcement layers of polyester fabrics, glass fiber or felt. The finished membrane thickness is referred to as mil thickness where 1 mil equals 0.001 inch. Typical membrane thickness range from 30 to 60 mils; however, greater thickness can be produced depending upon manufacturer and product type.

Single-ply thermo-plastic membranes will soften when heated and harden when cooled while thermo-set membranes are irreversibly set and will not soften when heated. Because of these fundamental differences single-ply membranes may be installed in the following ways:

  • Ballasted
  • Mechanically Attached
  • Fully Adhered

EPS roofing insulation can be installed as a component in almost all single-ply roof membrane systems. Polystyrene foam is subject to deterioration when subjected to petroleum-based solvents. Several single-ply membrane systems contain solvents that will attack EPS. Consult the membrane supplier to determine the compatibility of the membrane and installation adhesives with EPS foam.

EPS insulation can be mechanically fastened or fully adhered directly to a concrete roof deck with no thermal barrier and depending upon the membrane, the installation system may or may not require a coverboard. Ballasted systems may not need a coverboard, where as mechanically attached or fully adhered membrane systems typically will require a coverboard to provide additional strength for attachment fasteners or a barrier to petroleum vapors released from membrane sealing adhesives.

EPS insulation is available in thickness up to 40 inches, typically with square edges. Tongue and groove and shiplap edge details are also available. It can be tapered to 1/8 inch per foot to allow for adequate drainage on structurally flat roof decks. Typical thicknesses for roof applications are up to 12 inches. EPS insulation is available with a variety of compressive and flexural strength properties. Consult the current edition of ASTM C578 for the physical properties of specific EPS products types.


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