Published in Maintenance Solutions (March 1996)
Built-Up Roofing:  Industry Mainstay Endures

Built-up roofing (BUR) systems have seen a decline in market share over the past five years. The National Roofing Contractors Association (NRCA) reports in its 1995-1996 Annual Market Survey that built-up roofing accounts for 23.5 percent of new construction projects and 26.8 percent of reroofing projects. These figures ar down from the same report of 1990, where 30 percent of new construction projects and 34.1 percent of reroofing projects utilized built-up roofing.

This reduction in market share can be attributed to the growth in modified bituminous systems during the last five years. Modifieds have similar attributes, application techniques and performance to built-up systems.

System Trends - Built-up roofing system construction has remained relatively stable the past few decades. The last major change came in the 1970's and 1980's. Saturated organic felt reinforcement ply sheets started to be replaced by the fiberglass ply sheets, as the use of asbestos ply sheets came to an end.

Today, fiberglass ply sheets are the mainstay reinforcement of the BUR industry. A more recent trend has been the use of polyester as a reinforcement sheet. Fiberglass ply sheets are available in two common types; Type IV and Type VI.

Some manufacturers have promoted Type VI felts as being the "premium" felt. Experience with this product in the field, however, has shown Type VI felts to be stiff, so they do not conform well, especially at transitions. Type VI felts are also less porous, so the bitumen does not bleed through to encapsulate the fiber matrix as well as a Type IV felt allows. Type IV ply sheets are becoming widely accepted as the preferred ply sheet for built-up roofing.

Hybrid Systems - In response to market demand for modified bituminous systems, hybrid systems that combine traditional BUR technology with modified bituminous materials have gained popularity. These hybrid systems consist of two or more built-up plies of fiberglass ply sheets installed as the base, with one or more plies of modified bituminous sheets installed as a cap sheet.

Coal-tar based BURs still have a small market niche. Coal-tar reinforcing materials include asphalt-coated fiberglass felts, coal-tar saturated organic felts and coal-tar coated fiberglass felts. concerns in the industry with incompatibility in the use of asphalt fiberglass ply sheets with coal-tar bitumens, as well as the sinking of the fiberglass ply sheet in the coal-tar bitumen, has caused a renewed interest in coal-tar saturated organic ply sheets. Coal-tar fiberglass ply sheets also are popular choices.

Flashing Developments - Flashing materials for BUR systems have experienced an evolution over the past decade. Asbestos composition flashings and granulated organic cap sheets were mainstays in the past. Today, a variety of modified bitumen flashings are common. These materials are factory surfaced with granules, slate chips or foil, or they have a smooth surface to which a field-applied ultraviolet reflective coating is applied.

Cold process roofs, which use bitumens that do not require heating for application, have gained in popularity in recent years. These systems commonly incorporate polyester reinforcements.

Built-up Roofing Construction - Observation of work practices during the construction of built-up roofing is the best method of quality assurance. The key to this process is the experience of the person performing the observation. This person must not only be familiar with the contract documents, specifications and drawings, but must also have practical, hands-on experience with the roof system being installed.

Built-up roof systems have been a mainstay in the roofing industry for over a century. While the market share of traditional built-up roof systems may be declining, hybrid and modified bitumen roof systems similar to built-up roofs are gaining market share. Stability, durability and proven track records keep built-up roofs a popular choice among specifiers, contractors and building owners.