Roofing Commodities: Then and Now

The roofing industry has experienced the term “commodity” throughout its life. Examples include roofing asphalt, which is defined by ASTM Standard D312. To most specifiers, any roofing asphalt that meets D312 is fine for a hot-applied bituminous or modified bituminous roofing project. Over the years, asphalt producers have tried to insert product differentiation by introducing “low fuming” or other virtues. Such an example is Owens-Corning’s PermaMop:

In creating PermaMop modified roofing asphalt, we didn’t just one-up regular asphalts, we’ve three-upped them.

PermaMop is versatile. It’s specially formulated for use on any slope of roof. It has the softening point of Type IV asphalt but with a lower equiviscous temperature (EVT) than any standard Type IV. It stays where it’s mopped, even on steep-sloped roofing in intense heat.

PermaMop is long lasting. In laboratory testing, ordinary asphalt exceeds 60 weather cycles (approximately 15 years). PermaMop lasts a minimum of 150% longer – withstanding up to 193 cycles, making it an ideal choice for projects in extreme weather areas – whether it’s heat, cold or moisture.

PermaMop is low fuming. Its composition includes a technologically advanced polymer additive. When heated, the polymer floats to the surface and creates a skim layer on the kettle that traps the fumes and odor inside without affecting the asphalt or disrupting kettle operation.

Despite these obvious advantages, PermaMop costs more in a marketplace where price rules.PageBreak

Lack of Product Differentiation Throughout History

Another historical case of lack of product differentiation involves the bituminous saturated roofing felts used in conjunction with hot asphalt (or coal-tar pitch) in built-up roofing or as a shingle underlayment. Felts for hot roofing are covered by ASTM Specification D226, originally published in 1925. Modifications to D226 over the years included dropping the minimum percent saturation of the felts, recognizing that sources of organic fibers over the years have changed from rags and newsprint to sawdust (Asplund fibers) and waste paper, both of which are less absorbent than cotton fibers or newsprint previously used.

Low saturation implies less water resistance. A better indication of the quality of saturation is the Kerosine Number, which indicates the saturation efficiency, or what percent of the theoretical saturation is achieved. At one time, the minimum percent saturation of organic felts was 140-150%, but currently it is only 120%.

During the oil embargo of 1973-1974, asphalt was in short supply and rampant inflation led to price controls on commodity items. A major innovation in BUR was to introduce “new” products that could circumnavigate price regulations.

The saturated felts were coated with asphalt on both sides, reducing the plies to just two instead of four. Where were the savings? By only using two plies where four plies were used previously, savings were achieved on both material and labor.

Concepts such as “one plus one equals four” helped these two-ply roof systems gain traction, bypassing price controls. To cap the deception, these two-ply systems were supposedly bondable for 20 years, a marketing gimmick since none of these systems had anywhere near 20 years of field experience. The immense failure of these two-ply systems opened the floodgates to single-ply polymeric and modified bituminous systems.

The difference between ply-felts for hot roofing and shingle underlayment is mainly that the BUR felts are factory-perforated, permitting steam and entrapped air to escape during the lay-up process. These felts are designated by two types, No. 15 and No. 30 felt, even though the felts are actually lighter than 15 or 30 pounds per roofing square, respectively.

Shingle underlayments are not perforated, as they are a secondary weatherproofing and the holes would let water penetrate the building. Organic felt underlayments are covered by ASTM Standard D4869 and consist of four types:

As with asphalt itself, asphalt-saturated organic roofing felts are just a commodity item today, and the lowest price rules.

For shingle underlayment, a large number of engineered products are now offered in competition with the traditional No. 15 and No. 30 organic felts or the above-mentioned D4869 product types. Advantages cited for these new products include lighter weight, self-adhesion, higher tear strength, slip resistance, and in some cases, long-term exposure resistance. Many are based on non-woven mats with attendant resistance to moisture pick-up and wrinkling. Because the number of product choices is so prolific, the underlayment choice may be linked to the type of steep roofing (i.e. roofing slate, tile, wood or asphalt shingles, or metal pans) that follow.PageBreak

The Introduction of Glass Fiber Products

Product differentiation for hot BUR first took place when glass fiber roofing felts were introduced into both BUR and steep roofing.

Over the years, a number of versions of mats based upon glass fibers have been used in roofing. The earliest versions were steam-blown, which, despite their dimensional stability, were low in tensile strength and were restricted to the mild climates of the West Coast. An important advantage of glass-based roofing felts over organic roofing felts is that glass-based mineral-surfaced roof systems could meet Class B fire resistance when directly applied to plywood and OSB roof decks, but without the requirement of a bituminous flood coat and gravel surfacing.

A major innovation in glass mat development was continuous-strand glass fiber mats. These had far better tensile strength than the steam-blown mats and could be reliably used in any U.S. climate. Studies such as NBS BSS #55 confirmed that glass-based membranes could meet the proven performance of 4-ply organic membranes with the additional advantages of dimensional stability and good porosity, reducing the potential of wrinkling, ridging, and blistering.

As might be expected in the competitive roofing world, the proprietary continuous strand Perma-Ply R was challenged by a third generation wet-process glass fiber mat. The cost advantages of wet process resulted in the product dominating and eventually supplanting the R-mat. ASTM D2178 today defines just two types of mat, Types IV and VI, with tensile strength of 44 and 60 pounds per inch of width, respectively. The earlier steam mats are no longer shown at all and R-mat is no longer produced.

As you might suspect from the title of this column, wet-process mats are the low-cost commodities now. Specifiers assume that all the D2178 mats are the same and therefore seek the cheapest.

Polymeric Systems Debut in the Marketplace

Early polymeric systems, as their name implies, were to a great extent just a single layer with narrow seams. For the polyvinylchloride (PVC) systems, choices included internal reinforcement with scrim or glass mat or unreinforced. A commodity grade of non-reinforced PVC at a minimum thickness of 30 mils (0.030 inches) proved to be a terrible choice for the U.S. market. All non-reinforced PVC systems have been withdrawn, and the industry now pays a great deal of attention to having sufficient mil thickness over the scrim, as well as improved plasticizer systems.

Many of these early PVC systems were ballasted, a unique technique that the U.S. roofing industry was unfamiliar with at that time. These too have mostly disappeared, possibly due to extraction of the PVC’s plasticizer by the silt (i.e., dirt, especially clay-based) associated with the rock ballast.

Many polymers other than PVC were tried in single-ply versions. These included chlorosulfonated polyethylene (CSPE or Hypalon), chlorinated polyethylene (CPE), Tedlar film, butyl rubber, chlorobutyl rubber, neoprene rubber and various copolymer configurations. Of these, reinforced PVC (mechanically attached or fully adhered), thermoplastic polyolefins (TPO), and ethylene propylene diene monomer (EPDM, frequently ballasted) are the dominant single-ply systems in today’s competitive market.

All of these systems are cleaner and safer to work with than hot bituminous roofing. While PVC and TPO can be heat-fused to achieve watertight seams, they have the additional advantage of possessing very low VOC. PVC is inherently fire-resistant and to a large extent is recyclable.

EPDM is a true vulcanized rubber in which fine carbon particles (carbon-black) help reinforce the membrane. Black EPDM has proven that it can last over many decades. Fire resistance is achieved by adding fire retardants for exposed roof applications or by topping the roof with ballast (rocks don’t burn). EPDM is also recyclable.

TPO is a relative newcomer. As with PVC, it can be heat-welded, and it’s available in environmentally “cool” colors. As with PVC and EPDM, the TPOs continue to evolve. Unlike EPDM membranes that are essentially chemically equivalent, TPOs are all made according to different basic chemical formulations according to the desire of individual manufacturers.

For this reason, some TPOs perform better than others, and for that reason, TPOs are regularly being reformulated to address previously unseen issues, such as splitting at seams and creases, or recent concerns with heat degradation when installed under photovoltaic panels. ASTM Committee D08 is balloting right now on Standard D6878 for TPO, increasing the minimum thickness of coating over fabric or scrim (weathering side only) to 39 mils (0.039 inches).PageBreak

How Do They Measure Up?

So where do the PVCs, EPDMs, and TPOs stand on the commodity scale? As with the earlier bituminous systems, cost casts a large shadow. TPO is first in volume. Production has grown so rapidly that it’s already considered a commodity, that all TPOs are alike. But, of course, all TPOs are not alike. The new heat-resistant TPOs may provide some product differentiation, but if TPOs really need that heat resistance, we can expect rapid deployment of similar products.

Sheet thickness probably offers greater differentiation than polymer type. In the early days, 45 mil products were the standard, with an occasional 32 mil material, but when impact, static puncture, and traffic resistance are really needed, there are 60 and 90 mil products readily available.

New Materials and Coming Changes

In this discussion, we have skipped over the modified bitumen (MB) option. The polymer modifier differentiates these products: athermoplastic modifier, atatic polypropylene (APP), and an elastomeric modifier, sequenced butadiene-styrene (SBS). As a broad brush, both types use core reinforcement, with a coating of modified bitumen on both surfaces. Both are waterproof as they leave the factory, not relying on perfect application of hot bitumen in the field. Had these materials been available at the time of the oil embargo of 1973-1974, one plus one might have really succeeded.

Rather than rely on a flood coat of bitumen and field application of aggregate for water and weather resistance, MB surfacing may use mineral granules, metal foils, or even field-applied liquid coatings. Core materials may be polyester scrim, glass mat, or combinations. Application method can be by hot asphalt (SBS types), torch application (both SBS and APP), solvent-based adhesive, or even self-adhesion.

A major factor in all current roofing systems is the cost of petroleum (and polypropylene, as used in EPDM and APP modified bitumen). That, plus code changes that favor cool roofs, vegetated roofs, carbon neutral, low VOC products, and extremely high thermal resistance will probably differentiate what we use in this decade.

In the long run, a sub-committee of ASTM aims to streamline the process of choosing materials and systems. A committee is currently working on establishing the sustainability of roofing systems geared to specific project requirements. If this program is successful, we will have a narrow list of materials and systems to consider for a project and can relegate first cost and warranty length to the bottom of our list of criteria. 

Richard (Dick) L. Fricklas was technical director emeritus of the Roofing Industry Educational Institute prior to his retirement. He is co-author of The Manual of Low Slope Roofing Systems and continues to participate in seminars for the University of Wisconsin and RCI Inc. - The Institute of Roofing, Waterproofing, and Building Envelope Professionals. His honors include the William C. Cullen Award and Walter C. Voss Award from ASTM, the J. A. Piper Award from NRCA, and the James Q. McCawley Award from the MRCA. Dick holds honorary memberships in both ASTM and RCI Inc. 

Past, Present, Future: Roofing

Long ago, roofs only served a sole purpose of protecting structures. Today’s roofs, however, do much more than simply sheltering a building’s occupants.

Built-Up Roofing in this Decade

With increased interest in sustainability and green buildings, it’s only fair to look at the issues and see where BUR stands.

Thermoplastic (Heat-Weldable) Roofing

Learn about weldable single-ply systems, including thermoplastic polyolefin (TPO), polyvinyl chloride (PVC), ketone ethylene ester (KEE), chlorinated polyethylene (CPE), chlorosulfonated polyethylene (Hypalon or CSPE), and polyisobutylene (PIB).