Roofing material

The use of polymers as a roofing material is continuously increasing. The function of a roof is to protect the building from environmental factors such as light, wind, rain, snow loads, temperature changes, hail, and storms. Therefore, the material used on a roof must withstand those factors for many years. 

The performance of a material or system depends on the environment and the degrading effects to which it is exposed. Until the early 1990s, methods of measuring the properties and predicting the durability of products were not well known, hence, much of the knowledge about building materials was based on experience from long-time use. 

The NRCA s 2000-2001 Annual Market Surveyl reported that in 2000, the low-slope roofing market accounted for 64. l%ofthe total roofing market, a slight decrease from 68.7% in 1999. The roofing contractors predicted thatthe low-slope roofing market would be 63.3% in the year2001. 

Most types of roofing materials are bituminous and synthetic (polymeric) roofing membranes. The most commonly used roofing and waterproofing membrane is made by combining asphalt or coal tar pitch (bitumen) with felts or mats, or fabrics of organic or inorganic fibers. 

Roofs are a basic element of shelter from inclement weather. Natural or hewn caves, including those of snow or ice, ate early evidence of human endeavors for protection from the cold, wind, rain, and sun. Nomadic people, before the benefits of agriculture had been discovered and housing schemes developed, depended on the availabiUty of natural materials to constmct shelters. Portable shelters, eg, tents, probably appeared early in history. Later, more permanent stmctures were developed from stone and brick. SaUent features depended strongly on the avadabihty of natural materials. The Babylonians used mud to form bricks and tiles that could be bonded with mortars or natural bitumen. Ancient buildings in Egypt were characterized by massive walls of stone and closely spaced columns that carried stone lintels to support a flat roof, often made of stone slabs. 

For low slope commercial roofing, bituminous-based roof coverings are the most common systems in the United States. Asphalt-based materials predominate over coal-tar based materials in these systems. For residential roofing materials, various types of roofing products, including asphalt, wood, and tile, ate used for both new constmction and reroofing. 

Built-Up Roofing. Built-up roofing (BUR) is a continuous-membrane covering manufactured on-site from alternate layers of bitumen, bitumen-saturated or coated felts, or asphalt-impregnated glass mats and surfacings. These membranes are generally appHed with hot bitumens or cold apphed bituminous adhesives (qv). 

The deck may be nailable, eg, wood or light weight concrete, or not, eg, steel or stmctural concrete. The felts or mats may be organic (cellulose), or fiber glass. The roof slope ranges from dead level (0—2.1 cm/m), to flat (2.1—12.5 cm/m), to steep (12.5—25 cm, /m). 

Common BUR systems ate installed in different ways membrane adhered/attached to deck without insulation insulation adhered/attached to deck with membrane apphed to insulation base sheet adhered/attached to deck, insulation to base sheet, and top membrane to insulation and membrane adhered/attached to deck and insulation apphed over the membrane, the so-called protected-membrane roof 

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Data for thermal movement of various bitumens and felts and for composite membranes have been given (1). These describe the development of a thermal shock factor based on strength factors and the linear thermal expansion coefficient. Tensile and flexural fatigue tests on roofing membranes were taken at 21 and 18°C, and performance criteria were recommended. A study of four types of fluid-appHed roofing membranes under cycHc conditions showed that they could not withstand movements of <1.0 mm over joiats. The limitations of present test methods for new roofing materials, such as prefabricated polymeric and elastomeric sheets and Hquid-appHed membranes, have also been described (1). For evaluation, both laboratory and field work are needed. 

CommercialEow Slope Roofing Materials Guide, National Roofing Contractors Association, Rosemont, Dl. 

Extruded Rigid Foa.m. In addition to low temperature thermal insulation, foamed PSs are used for insulation against ambient temperatures in the form of perimeter insulation and insulation under floors and in walls and roofs. The upside-down roof system has been patented (256), in which foamed plastic such as Styrofoam (Dow) plastic foam is appHed above the tar-paper vapor seal, thereby protecting the tar paper from extreme thermal stresses that cause cracking. The foam is covered with gravel or some other wear-resistant topping (see Roofing materials). 

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