Roofing Glossary

	This glossary contains many useful terms and definitions. For easier browsing you can view our Photo Glossary, which has photographs of common roofing sites and problems, or you can browse the entire glossary by our alphabetical listing. A \| B \| C \| D \| E \| F \| G \| H \| I \| J-L \| M \| N \| O-P \| R S \| T \| U-V \| W-Z

Gable: a triangular portion of the endwall of a building directly under the sloping roof and above the eave line.

Gable-Shaped Roof: a single-ridge roof that terminates at gable end(s).

Gauge: a measurement of rating metal thickness.

Glass Felt: a sheet composed of bonded glass fibers, suitable for impregnation and coating in the manufacture of bituminous roofing and waterproofing materials, and shingles.

Glass Mat: a thin mat composed of glass fibers, woven or non-woven, with or without a binder. This mat may serve as reinforcement for certain roof materials and membranes.

Glaze Coat: (1) the top layer of asphalt on a smooth-surfaced built-up roof membrane; (2) a thin protective coating of bitumen applied to the lower plies or top ply of a built- up roof membrane when application of additional felts or the flood coat and aggregate surfacing are delayed. (Also see Flood Coat.)

Granule: (also referred to as Mineral or Ceramic Granule) opaque, natural, or synthetically colored aggregate commonly used to surface cap sheets, shingles, and other granule-surfaced roof coverings.

Gravel: aggregate resulting from the natural erosion of rock.

Gravel Stop: a low profile upward-projecting metal edge flashing with a flange along the roof side, usually formed from sheet or extruded metal. Installed along the perimeter of a roof to provide a continuous finished edge for roofing material. Acts as a bitumen-stop during mop application of hot bitumen along a perimeter edge.

Grout: a mixture of cement, sand, and water used to fill cracks and cavities in masonry.

Gutter: a channeled component installed along the downslope perimeter of a roof to convey runoff water from the roof to the drain leaders or downspouts.

Headlap: the distance of overlap measured from the uppermost ply or course to the point that it laps over the undermost ply or course.

Heat Transfer: the transmission of thermal energy from a location of higher temperature to a location of lower temperature. This can occur by conduction, convection, or radiation.

Heat Welding: method of melting and fusing together the overlapping edges of separate sheets or sections of polymer modified bitumen, thermoplastics or some uncured thermoset roofing membranes by the application of heat (in the form of hot air or open flame) and pressure. (See Heat Seaming.)

Hip: the inclined external angle formed by the intersection of two sloping roof planes.

Holiday: an area where a liquid-applied material is missing or absent.

"Hot" or "Hot Stuff": the roofer's term for hot bitumen.

Humidity: the amount of moisture contained in the atmosphere. Generally expressed as percent relative humidity (the ratio of the amount of moisture [water vapor] actually present in the air, compared to the maxi-mum amount that the air could contain at the same temperature.)

HVAC: heating, ventilating, and air conditioning equipment.

Hypalon TM : a registered trademark of E.I. duPont de Nemours, Inc., for "chlorosulfonated polyethylene" (CSPE). (See Chlorosulfonated Polyethylene.)

Ice Dam: a mass of ice formed at the transition from a warm to a cold roof surface, frequently formed by refreezing meltwater at the overhang of a steep roof, causing ice and water to back up under roofing materials.

Impregnate: to coat, saturate, and/or surround the fibers of a reinforcing mat or fabric with an enveloping liq-uid material, (e.g., bitumen, elastomeric compound, etc.).

Infrared Thermography: a practice of roof system analysis where an infrared camera is used to measure the temperature differential of a roof surface to locate areas of underlying wet or moist insulation. (See Thermal Image.)

Insulation: any of a variety of materials designed to reduce the flow of heat, either from or into a building. (See also Thermal Insulation.)

Internal Pressure: pressure inside a building that is a function of ventilating equipment, wind velocity, and the number and location of openings and air leaks.

Inverted Roof Membrane Assembly (IRMA TM ): a patented, proprietary variation of the "Protected Membrane Roof Assembly" in which Styrofoam Ž Brand Insulation and ballast are placed over the roof membrane. IRMA TM and Styrofoam Ž are registered trademarks of the Dow Chemical Company.

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