Singly-ply membrane are roof coverings manufactured in a factory and make up over 40% of new low-slope roof construction and 32% of re-roofing. These membrane are different than BUR membrane systems, which are built upon the roof from bitumen and other reinforcing fabric materials. Single-ply membranes can be thermo-plastic or thermo-set. Often these categories are identified by their chemical names, ethylene propylene diene monomer (EPDM) or polyvinyl chloride (PVC). Sometimes the membranes use reinforcement layers of polyester fabrics, felt, or glass fiber. The standard thickness of a membrane is usually between 20 to 60 mils (1 mil is equal to .001 in.) but can be thicker depending on manufacturer and product type.
Thermo-plastic single-ply membranes become harder when cooled and softer when heated, unlike thermo-set single-ply membranes which are fixed and cannot be hardened or softened. Single-ply membrane installation can be Ballasted, Mechanically Attached, and Fully Adhered.
When using EPS foam be sure to ask the membrane supplier if the membrane and installation adhesives are compatible with EPS foam. Polystyrene foam can deteriorate with the use of petroleum-based solvents and many single-ply membrane systems use solvents that will also compromise the integrity of EPS.
When using EPS the insulation can be fully adhered or mechanically fastened directly to the concrete roof deck without a thermal barrier. The installation may not require the use of a coverboard depending on the membrane. The coverboard typically provides additional strength for attachment fasteners for mechanically attached or fully adhered membrane systems. They can also act as a barrier to petroleum vapors released from the adhesives used to seal the membrane. Ballasted systems may not need a coverboard.
The thickness of EPS insulation is up to 40 inches and usually has square edges. Tongue and groove and shiplap edge details are also available. The foam can be tapered to ⅛ inch per foot in order to achieve adequate drainage on structurally flat roof deck. Generally, the thickness for roof applications are up to 12 inches. A variety of compressive and flexural strength properties for EPS insulation are available. For the physical properties of specific EPS products types consult the current edition of ASTM C578.
From: EPS Industry Alliance