Understanding Single Ply Roofing
Types of Single Ply Roofing
The term single ply roofing can be used to describe quite a few very different roof assemblies from modified bitumen to
PVC. Primarily this term is used to describe newer roof membranes such as EPDM (ethylene propylene diene monomer), a typically
black rubber membrane; PVC (polyvinyl chloride); and TPO (thermoplastic polyolefin). In simple terms, they are sheet products
delivered to the roof in roll form. These sheets or membranes are then rolled out and attached to the roof via adhesives
("fully adhered"), screws and plates ("mechanically attached") or weighted down by means of rock or pavers added on top of
the sheet ("ballasted").
Various types of Single-Ply membranes have been used for over 25 years. Some have performed extremely well while others
are non-existent today. Even membranes of the same type, such as PVC, have different characteristics from manufacturer to
manufacturer and have evolved tremendously over the more than 25 years that they have existed. Some early PVC membranes
failed so badly in Colorado's harsh environment that we still hear people refer to them as “those sheets that shatter.”
The chemical make-up of the modern PVC’s, as well as the processes used to manufacture them, have improved tremendously,
and current PVC membranes are completely different from those early versions. The primary differences between the new
generation of these white roofs and those that failed years ago are the improvements in plasticizers and UV stabilizers.
The fact that they are reinforced with fiberglass or polyester scrims also makes a noticeable difference. The new generation
of single ply roofs stay flexible, strong, and tear resistant.
PVC and TPO membranes are both thermoplastic sheets, which means that they can be heat welded. The welded seams of a
properly installed thermoplastic membrane are usually stronger than the sheet itself. In the past, it was the seam on the
thermoset membrane, such as EPDM, that failed far before the membrane itself had lost its waterproof quality and flexibility.
In recent years, the manufacturers of EPDM membranes have improved the seaming procedure and materials so that seam failure
is much less an issue with a properly installed EPDM roof.
Both PVC and TPO membranes are usually white although many manufacturers are now offering these in a variety of colors.
The white sheets have benefits due to their reflective nature. The Department of Energy as well as many other testing and
certification entities have labeled these as being “cool roofs” due to their ability to lower interior temperatures and
utility costs as compared to a darker roof type.
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