Single-Ply Roofing Systems

Single-Ply Roofing Systems

Today, several varieties of single-ply systems are on the market. Some have now been available for almost two decades. Single-ply systems are categorized into two generic types: First, thermoplastic membranes are sheets where chemical crosslinking does not occur. Thermoplastic materials are seamed by either hot air or solvent welding of one sheet to the next creating a direct bond of the material. Second, thermoset membranes are those that chemically cross-link (i.e. cure). Most thermoset materials are seamed with an adhesive since the cured material cannot be chemically linked. The common formulations of these categories are as follows:

Thermoplastic

• Polyvinyl chloride (PVC)
• PVC Alloys
  • Copolymer alloy (CPA)
  • Ethylene interpolymer (EIP)
  • Acrylonitrile butadiene polymer blend (NBP)
• Chlorinated polyethylene (CPE)
• Polyisobutylene (PIB)

Thermoset

• Neoprene
• Chlorosulfonated polyethylene (CSPE)
• Epichlorohydrin (ECH)
• Ethylene propylene diene terpolymer (EPDM)

EPDM Roofs

Ethylene Propylene Diene Monomer (or Terpolymer which is simply a product consisting of three distinct monomers). EPDM is classified as a Thermoset material which means it is either fully-cured prior to being installed or that it cures during natural weathering after installation. EPDM roofs are single-ply membranes meaning there is only one ply of roofing material, not multiple plies laminated together. 

EPDM has been in use on roofs in the USA since the 1960's and is one of the most common types of low-slope roofing materials. This is because it is relatively inexpensive, simple to install, and fairly clean to work with when compared to conventional built-up roofs. There aren't the odors and fumes that accompany built-up roofs which appeals to many property owners and managers.

EPDM is a rubber material whose principal components consist of the compounds ethylene and propylene. A flexible rubber matrix forms when a small amount of diene is added to the mix. EPDM is available reinforced or unreinforced with both commonly used; it's also available in either a cured (vulcanized) or uncured (non-vulcanized) state. Vulcanized EPDM is the most common with non-vulcanized often used for flashing purposes.

PVC Roofs

PVC membrane is a roof membrane composed of only one layer of material, polyvinyl chloride. PVC roofs are specially designed to withstand ponding water- PVC membrane is welded together with hot air (no open flame) to eliminate all seams so moisture can not pass through.

PVC roofing systems also reflect nearly 90% of the heat of the sun, thus lowering energy costs substantially, especially in high-heat areas such as the southwestern United States.

Pros:

• Fire safe material
• Energy Efficient
• Good weather resistance
• Good long-term performance for a low slope roof

Cons:

• Not intended for high rain or snow areas

TPO Roofs

Thermoplastic Olefin or Polyolefin

TPO membranes are single-ply roof membranes constructed from ethylene propylene rubber. They are designed to combine the durability of rubber with the proven performance of hot-air weldable seams. They have been tested as having excellent resistance to ozone, are algae-resistant, environmentally friendly and safe to install.

The material's manufacturers are so confident in properly welded seams that the material is sometimes advertised as a monolithic (seamless) roof. Seam strengths are reportedly 3 to 4 times those of EPDM's adhesive and tape seams. TPO is highly resistant to tears, impacts, and punctures with good flexibility to allow for building movement. TPO's are available in white, light gray, and black with thicknesses of either 45 mils (.045") or 60 mils (.060"). The width of the membrane depends on the manufacturer but they usually come in widths of six to six-and-a-half feet and are one-hundred feet in length.

TPO membranes are installed fully-adhered, mechanically-attached or ballasted. Fully-adhered means that the roof is "glued" to the substrate using a special adhesive. What actually happens is the glue creates a chemical bond with the membrane. Ballasted simply means the membrane is loose laid over the top of the roof, sealed at all penetrations and around the perimeter, and then a ballast is put on it to hold it in place.

Ballast usually consists of smooth, round, river rock 2" - 3" in diameter and is applied at a rate of 1,000 to 1,200 pounds per roof square (100 sq. ft.). Sometimes concrete pavers are used in their place. These average 20 pounds per square foot. Mechanically-attached membranes are those that use some type of special screw-type fastener to secure it. The type of fastener will depend on the type of substrate but all fasteners are generally screw-type fasteners.

References

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