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 build-up roofing.
Tillotson Enterprises uses a fabric-reinforced ply system. By using an elastomeric liquid applied coating, we form a seamless waterproof membrane with the durability and tensile strength seen with a conventional single-ply system. 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 Enterprises’ 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.
Read about Single Ply Roof System Comparisons
The most common application for single-ply roof systems is over tar or tar and gravel roof systems, as these can 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. 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. There are a variety of chemistries for single-ply materials.
In layman’s terms, 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.
The first roof system lays insulation board 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.
The second roof system 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). These screws are, in addition to the screws that are already holding down the sheet itself.
The third roof system is called fully adhered or glued in place. In this application, the insulation board is 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.
- 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.
- We often see screws back out of the roof deck due to expansion and contraction of the roof. They eventually poke their heads up through the sheet itself, creating holes that water can seep through.
- Weather cracking, caused by temperature fluctuations making the sheet brittle after several years.
- 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.
- The seams of EPDM are sealed with water-soluble glue which can cause seam failure over time.
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. These systems are usually mechanically fastened, and although they do not shrink, 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 (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.
Hypalon is a system that cures on the roof and does not become weak and brittle like other single-plys, making it one of the best sheet systems on the market. It can be held down using a ballast, mechanically fastened, fully adhered, or held in place with air pressure. Mechanically fastened is by far the most popular method. This sheet is also heat welded at the seams. Hypalon sheets are very chemically resistant and are the roof of choice in cases where chemicals may be deposited from vents or pipes. However, as with all single ply systems, once it has a hole in it, water is free to migrate.