Single Ply Roof System

The majority of new roof applications now use a ply system instead of a built-up roof (BUR) because they are usually more cost efficient, longer lasting, and lighter than built-up roofs. These systems are perfect for flat or low-sloped roofs, and can be applied to exterior grade plywood, high density concrete, or smooth surface like a build-up roofing.

Tillotson Enterprises uses a fabric-reinforced ply system. By using an elastomeric liquid applied coating, Tillotson form a seamless waterproof membrane with the durability and has great tensile strength (resistant to puncture). The reinforced fabric gives extra strength to the finished product, making a waterproof system without adding significant weight.

Due to the fact that not all roofs are alike, ply systems are custom-built on site. By embedding fabric between multiple layers of specified roof coating material, Tillotson ply systems are made to meet the unique needs of each roof.

With its reflective, energy-saving white elastomeric top coat, the completed ply system will stand up against harsh weather conditions and offer durable, long-lasting protection.

Single Ply Roof System Comparisons

About half of the low slope (or flat) roofs in the Midwest use a single-ply roof technique. This is due in part to the relatively minimal equipment cost and experience required by the contractor to install, as well as the relatively low material cost. On most sheet systems the cost of the sheet is only 25% of the total bid.

The most common application for single-ply roof systems is over tar or tar and gravel roof systems, as these roof systems wear out. Single-ply roof systems are also installed over other single-ply roof systems that have deteriorated.

Sometimes, single-ply roof systems are installed over metal roofs, but this is not a recommended application by Tillotson. To make this work, boards must be screwed or glued down to fill the flute of the metal, insulation board is installed over that, and finally, the single-ply sheet is installed on top. Thousands of new holes have just been made by doing this, and now there is only a thin layer of material keeping water out, the single ply sheet itself. There are a variety of chemistries for single-ply materials.

EPDM

EPDM (ethylene propylene diene monomer) is called a “rubber” roof because it is usually made of black vulcanized rubber much like the old car or bicycle inner tubes. These roof systems are designed to work in one of three ways.

• Ballasted: lay of insulation board or recovery sheet on top of the roof deck. The rubber sheet is then placed directly on top of the insulation board and held down by what is called ballasted material (usually river rock) which can weigh from 8-12 pounds per square foot depending on code specifications.
• Mechanically fastened: Involves mechanically fastening the insulation board to the rubber sheet with screws and plates that are spaced at least every two feet (depending on wind uplift ratings) on the insulation board. The screws and plates that hold down the sheet itself are usually spaced every 5 feet in a row.
• Fully Adhered: This roof system is fully adhered or glued in place. In this application, the insulation board is usually mechanically fastened down and the rubber sheet is then adhered with slow rise foam or some other form of adhesive.

While there are cost advantages to EPDM roofing, there are also significant disadvantages.

1. These systems can shrink as much as 6% per year. This causes pulling on the edges of the building which in turn causes termination bars, parapet walls and side walls to be pulled out. Seams can be pulled apart and vent pipes can be pulled over, among other problems.
2. We often see screws back out of the roof deck due to expansion and contraction of the roof. Screw heads eventually poke up through the sheet itself, creating holes that water can seep through.
3. Weather cracking caused by temperature fluctuations making the sheet brittle after several years.
4. Wind damage, which often goes unnoticed on ballasted and glued roofs. Over time, the wind can cause the sheet to become unfastened from the substrate.
5. The seams of EPDM are often sealed with water-soluble glue which can cause seam failure over time.

PVC

PVC (polyvinyl chloride) sheet systems are typically white or tan in color and are usually fabric reinforced to make them stronger than EPDM roofing. However, in our experience, the chemical makeup of these systems can cause them to become brittle with age being exposed to the sunlight. These systems are usually mechanically fastened, and although they do not shrink like EPDM, they have many of the same problems as an EPDM roof: screws can back out creating holes; and wind damage is not uncommon.

On a positive note, the PVC sheet is usually white, which reflects rather than absorbs the sun’s energy. The seams are also heat welded, rather than glued, which results in a significantly stronger seam.

TPO

TPO (Thermoplastic Olefin) is a relative newcomer to the single-ply market. TPO was designed to replace EPDM at the low end of the market, because PVC roof systems are typically higher in cost than an EPDM roof. The overall performance for TPO is generally in between an EPDM roof and a PVC roof.