Section 6: SINGLE-PLY ROOFING SYSTEMS
Single-Ply Roofing Description. A membrane, sheet or
liquid-applied, with only a single layer of material designed to
resist water penetration.
Single-Ply Sheet-Applied Materials. Sheet-applied
membranes can be chemically classified in one of the following
categories: elastomers (synthetic rubber), plasticized
thermoplastic polymers, uncured elastomers, or modified bitumens.
(Refer to Table 1 for membrane adaptability to different roof
Elastomeric Sheet. The most common elastomeric sheet
is ethylene propylene diene monomer (EPDM).
Field lap seams are the most vulnerable component in
elastomeric sheet systems. EPDM is a thermosetting polymer and
requires use of contact adhesive and tape. Contact adhesive
thorough cleaning of the material with solvent-
b) a waiting period for the contact adhesive to attain
thorough pressure-sealing of the lap; and
d) application of a side lap sealant for temporary
protection while the contact adhesive cures.
Defective seams are vulnerable to rainwater ponding,
especially frozen water. Prolonged water intrusion impairs the
performance of neoprene-based contact adhesives. Non-neoprene-
based adhesives are significantly less vulnerable to moisture
Plasticized Thermoplastic Sheets. Plasticized
thermoplastic sheets are represented by PVC membrane sheets,
reinforced and unreinforced. Watertight field lap seams are
formed in PVC sheet by comparatively easily installed solvent-
welded or heat-welded lap seams. These seams are true fusions of
base and jointing material.
A major liability of PVC sheet membranes is that they
may, under certain exposures, become embrittled and shrink from