After more than 17 years in business, we’ve encountered a wide variety of roofs on commercial buildings. Some are metal roofs while others are tar and asphalt; some are pitched while others are flat; some are in good basic condition while others have serious problems.
What we’ve found is that no roofing system is ideal in all cases. At Tillotson Enterprises, we take the time to sit down and discuss all your options with you and arrive together at the best solution for your building.
Following is a brief discussion of the pros and cons of the various systems offered by Tillotson Enterprises and our competitors.

Single Ply Roofing Systems
About half of low slope (or flat) roofs in the Midwest are done using a single-ply roofing technique. This is due in part to the relatively minimal equipment cost and experience required by the contractor, 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 is over tar or tar-and-gravel roof systems as they wear out, although single-plys are often installed over other single-ply roofs as they deteriorate.
Sometimes single ply systems are installed over metal roofs, but we don’t recommend this application. To make it work, board must be screwed or glued down to fill the flute, insulation board installed over that, and finally installing the single-ply sheet on top. Thousands of new holes have just been made with only a thin layer of material keeping water out.
There are a variety of chemistries for single-ply materials.

EPDM – In layman’s terms EPDM is called a “rubber” roof because it is usually made of black vulcanized rubber — like the old car or bicycle inner tubes. These systems are designed to work in one of three ways.
The first is to lay insulation board on top of the roof deck with the sheet placed directly on top of the insulation board and then held down by what is called ballasted material (usually river rock) weighing up to 8-12 pounds per square foot depending on code.
The second application involves mechanically fastening the insulation board to the rubber sheet with screws and plates at least every two feet (depending on wind uplift ratings) in addition to the screws that are holding down the sheet itself.
The third system is called fully adhered or glued in place. In this application the insulation board is usually mechanically fastened and the EPDM sheet adhered with slow rise foam or other adhesives.
While there are cost advantages to EPDM, there is also a significant downside.
First, 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 to be pulled apart, and vent pipes pulled over among other problems. Second, we often see screws back out of the roof deck and poke their heads up through the sheet itself, making holes through which water can seep. Third is the problem of weather cracking caused by huge temperature fluctuations which can make the sheet brittle after several years. Fourth is wind damage, especially prevalent on ballasted roofs. Lastly, the seams of EPDM are sealed with a water-soluble glue that can cause seam failure over time.

PVC – These sheet systems are typically white or tan in color and are usually fabric reinforced to make them stronger than EPDM. However, in our experience, the chemical makeup of these systems can cause them to brittle with age. These systems are usually mechanically fastened, and although they don’t shrink, they have many of the same problems as EPDM: screws back out making holes, and wind damage is not uncommon.
On the positive side, the PVC sheet is usually white, which reflects rather than absorbs the sun’s energy. The seams are heat welded, rather than glued, which results in a significantly stronger seam.

TPO – Thermoplastic Olefin (TPO) is a relative newcomer to the single-ply market. TPO was designed to replace EPDM at the low end of the market because PVC’s are typically higher in cost then an EPDM roof. Overall performance for TPO is generally in between EPDM and PVC.

Hypalon – These are the best of the sheet systems on the market today, because Hypalon cures on the roof and does not become weak and brittle like other single-plys. It can be held down using ballast, mechanically fastened, fully adhered, or held in place with air pressure, although mechanically fastened is by far the most popular. 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. However, as with all single ply systems, once it has a hole in it, water is free to migrate anywhere.

Spray Polyurethane Foam
Spray Polyurethane Foam (SPF) is applied using a special spray gun that mixes two chemicals as they exit the barrel, causing a chemical reaction that produces the end product. Foam is usually applied in thicknesses from one inch to several inches. Polyurethane foam is a plastic and is waterproof after it is applied, however, it needs protection in the form of a top-coat or layer of rock to help it resist the UV rays in sunlight and keep it from deteriorating.
SPF can be made as soft as a pillow or so hard that you can drive a nail into it. Foam used for roofing is soft enough to be able to move with the expansion and contraction of the roof but hard enough to withstand foot traffic, impact, wind and weather. Foam is flexible and can go over different substrates with ease.
As a roofing material, SPF is difficult to beat if good quality coatings are used and properly applied. If, on the other hand, substandard equipment is used and the ratio between the chemicals is incorrect, it can cause bubbles in the foam. The same problem can occur from applying roofing over a wet substrate. Tillotson Enterprises applies SPF to a depth of no less than 1-1/2 inches, half again the minimum one inch recommended by the Society of the Plastics Industry (SPI). Some contractors will apply a half-inch or less.
Among the advantages to SPF is that it creates a continuous seamless membrane, with every square inch fully adhered to the roof deck. Thus, if a puncture is created in the coating layer it will not create a leak. In fact, if a hole is made clear through to the roof deck, a leak still may not occur, because foam is fully adhered. Yet if the same hole were formed in a single-ply roof, the water can spread throughout the roof deck, finding any number of holes caused by screws holding down the sheet system.
SPF roofs are also referred to as a renewable roof system because even if the roof has gone too long without attention, bad areas can be cut out and reformed and settled areas can be filled in with more foam.
The big saving In SPF roofs, however, comes from energy efficiency. Each inch of foam roof has an R-value of around 7, and the roof surface is white which helps reflect sunlight and make the roof cooler. Most SPF systems pay back the cost of the roof, in energy savings alone, in just a few years.
In addition, years down the road, the cost to re-roof over SPF will be substantially less expensive than roofing over other systems.