Volume 29, June 1997 PVC Membrane Shattering — A Reminder Benchmark

Volume 29, June 1997 PVC Membrane Shattering - A Reminder Benchmark

PVC Membrane Shattering — A Reminder

by: Jeff Evans, RRC

In preparation for a recent arbitration hearing for a dispute over a troubled non-reinforced PVC membrane roof, it struck me that the PVC shattering issue has received less discussion in roofing trade and other building management magazines. When a non-reinforced PVC roof shatters, the building can suddenly be left without a roof, and completely exposed to the elements. If you have a non-reinforced PVC membrane roof system on your building, or are not sure you do, read on.

Non-reinforced PVC membranes were marketed in the United States by a number of different companies. Dynamit Nobel (Trocal pre-1988), Barra Corporation, Plymouth Rubber, and General Tire (Genflex), were a few of the manufacturers. The marketing of non-reinforced PVC membranes gradually diminished to near zero by the late 80s. So if your PVC roof is less than 10 years old, it is probably reinforced with fiberglass or polyester scrim and is not the subject of this article.

Identifying Non-reinforced PVC

Most non-reinforced membranes were installed in either a ballasted or mechanically fastened application. The membrane is typically gray or white if exposed (mechanically fastened), or may be beige, if covered with gravel ballast. A close examination of clean membrane shows it to be smooth in texture, with no fabric or textile pattern on the sheet. The perimeter metal and roof penetration flashings may consist of gray PVC coated metal, but not always.

Mode of Failure

PVC membranes start as a rigid material, and are made flexible by adding plasticizers. The plasticizers add not only elastic qualities, but cold temperature flexibility. UV stabilizers, colorants, biocides, and filler are also added to the plasticized PVC formula.

As a PVC membrane ages, some plasticizer is lost through migration, evaporation and hydrolysis. A certain amount of plasticizer loss is anticipated, without affect on the membrane’s performance. If low cost, low molecular weight plasticizers are used in the formulating of the sheet, the rate of loss of plasticizers can be unacceptable. This can result in membrane embrittlement, shrinkage and an increase in temperature-induced loading.

Failure begins with loss of plasticizer, which causes the roof membrane to lose thickness and induces shrinkage. Tension on the membrane caused by plasticizer loss is added to by normal temperature variations. Shattering can occur during periods of cold temperature, and is often precipitated by walking on the membrane, hail, wind, or some other mechanical damage. There are cases where no precipitating event was noted, and the roof membrane fractured without warning. Membrane damage may be localized splits, or may be widespread, fragmentation of the membrane.

Signs of Failure

There are not always tell-tale signs predicting PVC shattering. However, of the hundreds of PVC shatters documented, some did indeed show premature failure signs,including:

  • Displacement of flashings/failure of nailer attachment
  • Discoloration of the membrane
  • Volume 29, June 1997 PVC Membrane Shattering - A Reminder Benchmark
  • An unusually taut membrane
  • Elliptical holes in baseflashing coverstrips
  • Half moon tears in the membrane, around fastener heads (on mechanically attached systems)

There are also reports of otherwise flawlessly performing roofs shattering without signs of failure.

Action Plan

The level of care of a non-reinforced PVC membrane system has only a marginal affect on the system’s longevity, since the main cause is plasticizer loss. There is little an owner can do to influence this loss rate; it is inherent to the product. There are a few loss prevention techniques that can minimize the possibility of shattering:

  • Do not allow roof traffic when roof temperatures are below 50 degrees Fahrenheit
  • Remove all sharp objects, debris, etc. from the roof
  • Be certain all roof mounted equipment is well secured against wind forces

It’s our opinion that shattering is the most likely mode of failure of this type of roof system, if the system is allowed to go to failure. This opinion is shared by many in the industry. As a result, when non-reinforced PVC membranes reach their 8th to 12th year of service, it may be most wise to consider proactive replacement.

The shattering problem with non-reinforced PVC membranes will eventually work itself out, as these roofs are no longer being sold today, and older non-reinforced roofs are being replaced. We should also note that reinforced PVC membranes are not subject to sudden shattering, and we have not observed similar problems with these systems.

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