Roof Systems

L. I. Knab, D. R. Jenkins, and R. G. Mathey, "The Effect of Moisture on the Thermal Conductance of Roofing Systems," NBS Building Science Series 123, National Bureau of Standards, U.S. Dept, of Commerce, Washington, D.C., Apr. 1980. 

Single-ply membranes offer the widest range of systems in the roofing industry. The three basic systems are ballasted, fuUy adhered, and mechanically fastened. From a cost standpoint, the fuUy adhered system is the most expensive to install, the ballasted system the least. The protected-membrane roofing system can be used with any of the basic systems. The specifications for these systems are pubHshed by the various manufacturers. The following gives a brief description of the roof assembhes. 

Fleece-Back Sheet. A fleece-back sheet is a nonreinforced polymeric membrane that has had a nonwoven mat made of polyester, weighing 101.7—203.4 g/m, laminated to the back of the sheet. The prime use of the fleece-back sheet is in the fully adhered roofing systems. The fleece provides the chemical separator, which eliminates the need for an adhesive that is compatible with the specific membrane or a compatible substrate. 

EPDM is by far the most widely used material in the ballasted roofing system constmction. Because of EPDM s flexibiHty, very large sheets of up to 10,000 square feet (929 m ) can be deHvered to the job site in compact roUs that offer reduced labor on the roof in the seaming process. The typical EPDM sheet size used in ballasted systems is 12 by 30 m and 1.1 mm thick. EPDM is also widely used in both the fully adhered and mechanically fastened roofing systems. In these constmctions, both 1.1- and 1.5-mm thick material is used with widths from 2.1 to 15 m. A majority of the installations use nonreinforced sheet, although reinforced membrane can also be used in all of the system types. The majority of the reinforced sheets go into mechanically fastened systems. 

BP. These nitrile alloy membranes are compounded from PVC, flexibilized by the addition of butadiene—acrylonitrile copolymers, PVC, and other proprietary ingredients. Typically reinforced with polyester scrim, NBP membranes are 1 mm thick and have a width of 1.5 m. They ate ptedominandy used in mechanically fastened roofing systems. NBP membranes exhibit excellent teat and puncture resistance as well as good weatherabihty, and remain flexible at low temperatures. They ate resistant to most chemicals but ate sensitive to aromatic hydrocarbons. The sheet is usually offered in light colors. The physical characteristics of NBP membranes have been described (15). 

The greater portion of PVC is installed in the mechanically fastened roofing system a lesser portion is installed in fully adhered appHcations. Although PVC was once heavily used in ballasted roofing systems, there are only a small number installed in the 1990s. Fleece-back membrane is popular in the PVC constmction for both fully adhered appHcations as well as in appHcations where a separator sheet is needed. PVCs ate resistant to vafious weather conditions, bactefial growth, and industfial chemicals. These membranes ate chemically incompatible with bituminous materials. PVCs ate offered in a variety of colors. The physical characteristics of a PVC membrane have been described (15). 

ANSI RP-4, Wind Design Guide for BaUasted Single-Ply Roofing Systems, ANSI, New York. 

H. O. Laaly, The Science and Technology of Traditional and Modem Roofing Systems, Los Angeles, Calif., 1992. 

Eoss Prevention Data, Mdhered or Mechanically Mttached Single-Ply Membrane Roof Systems 1 —29, Eactory Mutual System, Norwood, Mass. 

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). 

In addition to the paving grades of emulsions, a variety of products are available that are suitable for industrial uses, for paper sidings, and for use in the roofing appHcation field. Asphalts emulsified with colloidal clays are especially suitable for outdoor appHcations because of their exceUent weathering properties. Some of these products have been adapted for use with roofing systems, either with bmsh or spray appHcation. 

Type IV asphalt is not common except in very hot climates. It has softening points between 96 and 107°C with penetration at 25°C between 12 and 25 mm /10. It is for roof slopes greater than 1 per 12, and is also called special steep asphalt. Type IV asphalt is used on flashings and in hot climates to keep the roofing system from sliding off the roof in hot weather. 

Thermoset polyurethane as a biader material for gravel systems is also under development. AppHcations could iaclude roofing systems that requite a high degree of uv light and abrasion resistance. 

Floor, wall, and roof systems for light-frame construction. 

A series of separate SDOF dynamic analyses are performed for each of the primary structural components. For example, a typical roof system consists of a roof slab supported on structural steel roof beams which are in turn supported by roof girders. Separate SDOF dynamic analyses are performed for the slab, beams and girders using the reaction time history of the supported member as loading input 10... 

Development of a glossy, aesthetic and unpainted roof module on the Smart Roadster by DaimlerChrysler AG s Smart. The two-piece, removable roof, built by ArvinMeritor, is surfaced with a thermoformable three-layer film (Lexan by GE Plastics) that can be co-moulded with either thermoplastic or thermoset substrates. The film exhibits 95% gloss retention after the equivalent of 10 years of Florida sun exposure. Weight saving is 50% versus a painted steel roof system. 

New Orleans, La., 21st-24th Oct.1992, p.400-9. 43C6 ROOF SYSTEM EFFECTS ON IN-SITU THERMAL PERFORMANCE OF HCFC POLYISOCYANURATE INSULATION Christian J E Desjarlais A O Courville G Graves R Oak Ridge National Laboratory (SPI,Polyurethane Div.)... 

Nonreinforced. Many nonreinforced elastomeric membranes are available. These allow the roofing system to take full advantage of the elongation, which can be as much as 600%, of the elastomeric membrane. This works to its fullest advantage in handling building movement as well as thermal and other stresses. The nonreinforced membranes are most popular in ballasted roofing systems. 

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