G-90: A coating weight for galvanized sheet metal, 0.90 ounces of zinc per sq. ft., measured on both sides of the sheet.

Gable: A triangular-shaped portion of the end wall of a building, formed by the sloping roof and above the Eave line.

Gable Roof: A roof configuration in which two planes slope so as to form a triangle.

Galvalume: Trade name for a protective coating composed of aluminum zinc.

Galvanic Action: A reaction between different metals in the presence of an electrolyte.

Galvanize: To coat with zinc.

Galvanized Steel: Steel that is coated with zinc to aid in corrosion resistance. Galvanized steel for use in roofing should be Hot-Dipped Galvanized with a G-90 coating.

Gambrel: A roof that has two different pitches.

Gauge: A standard of measurement. For instance the thickness of sheet metal or the diameter of wire. The thicker the wire or metal, the lower the gauge.

Geodesic Dome: A geodesic dome is constructed of a series of self-bracing triangles composed in a pattern that lends maximum structural advantage, thus theoretically using the least material possible. (A "geodesic" line on a sphere is the shortest distance between any two points.)

Glass Felt: (1) In the manufacturing of roofing materials - a sheet comprised of bonded glass fibers prior to being saturated with bitumen; (2) short for asphalt or coal tar saturated fiberglass felt membrane.

Glaze Coat: (1) The uppermost layer of asphalt on a smooth-surfaced built-up roof membrane, usually a reflective surfacing is installed over it; (2) A thin coat of bitumen applied to help protect the roof membrane when application of additional felts or the flood coat and aggregate surfacing must be delayed.

Granule: A small aggregate, naturally or synthetically colored, used to surface cap sheets, shingles, and other granule-surfaced roof coverings.

Gravel: Aggregate consisting of rock fragments or pebbles.

Gravel Stop: A flanged, sheet metal edge flashing with an upward projection installed along the perimeter of a roof to prevent the migration of gravel or bitumen over the roof edge.

Gutter: A channel (usually sheet metal) installed along the low perimeter of a roof to convey runoff water from the roof to the rain water leaders or downspouts.


Hatch: A unit used to provide access to a roof from the interior of a building.

Headlap: The minimum distance, measured at 90 degrees to the eaves along the face of a shingle or felt, from the upper edge of the shingle or felt to the nearest exposed surface.

Heat Transfer: Thermal energy transferring from an area of higher temperature to an area of lower temperature by conduction, convection, or radiation.

Heat Welding: Fusing the seams of separate sections of roofing material together through the use of hot air or an open flame and pressure.

Hem: The edge created by folding metal back on itself. Metal is hemmed to eliminate sharp edges and increase rigidity.

Hip: The angle formed at the intersection of the sides of two sloping roof planes.

Hip Roof: A roof that rises by inclined planes on all sides of a building. The line where two adjacent sloping sides of a roof meet is referred to as the Hip.

Holiday: An area where a liquid-applied material is missing.

Honeycomb: Small voids left in concrete because the mortar failed to fill the spaces around the aggregate.

“Hot”: Slang for hot bitumen.

Humidity: The amount of water vapor in the air.

HVAC: Acronym for Heating, Ventilating, and Air Conditioning.

Hypalon: The trademark name for Chlorosulfonated Polyethylene (CSPE), which is used as a single-ply roofing material.


ICBO: International Conference of Building Officials, responsible for The Uniform Building Code.

Ice Dam: Ice formed at the transition from a warm surface to a cold surface, such as along the overhang of a house. The build-up of ice is the result of ice or snow melting on the roof area over the warmer, living area of a building and then refreezing when it runs down and reaches the overhang.

Ignition Temperature: The minimum temperature at which a material will combust.

Impact Resistance: A roof assembly’s ability to withstand the impact from falling objects such as hail.

Impregnate: To saturate; in roofing, asphalt impregnated fiber glass roofing felts are fiber glass mats that have been completely permeated with asphalt bitumen.

Incline: Roof slope. Generally expressed either in percent or in the number of vertical units of rise per horizontal unit of run. For example, a 6:12 Incline would indicate that the slope rises 6 inches for every 12 inches in vertical run.

Infrared Thermography: The use of an infrared camera to detect temperature differences. In roof insulation, temperature differences can be used to isolate areas contaminated with moisture.

Inorganic: Involving neither organic life nor the products of organic life; relating to compounds not containing hydrocarbon groups.

Insect Screen: Material used to inhibit an insects ability to enter a building through openings in a roof such as vents.

Insulation: Material used to help maintain a certain temperature in a building by reducing the flow of heat to and from that building. See also Thermal Insulation.

Intake Ventilation: The part of a ventilation system used to draw fresh air in. Usually vents installed in the soffit or along the eaves of a building.

Interlayment: A waterproof material usually installed between adjacent rows of wood shakes to help with the roof’s waterproofing characteristics.

Interlocking Shingles: Shingles that lock together to provide wind resistance. See also T-Lock.

Internal Pressure: Atmospheric pressure inside a structure that correlates to the number and location of openings and air leaks.

Inverted Roof Membrane Assembly (IRMAŽ): A variation of the "Protected Membrane Roof Assembly" in which StyrofoamŽ brand insulation is used. IRMAŽ and StyrofoamŽ are registered trademarks of the Dow Chemical Company. Sometimes referred to as an “Upside Down Roof” since the insulation is installed on top of the roof membrane.


Job Average Basis: A technique for determining the average dimensions or quantities of materials, by analysis of roof test cuts. The technique requires a minimum of three test cuts per roof area, plus one cut for each additional 10,000 square feet of roof area. Job-average basis is computed by dividing the sum of all measurements taken by the number of measurements taken. The results would describe the job-average for the quantity or dimension.

Joint Tape: Tape used to seal joints between insulation boards.

Joist: Any of the parallel horizontal beams set from wall to wall to support the boards of a floor, ceiling or roof of a building.


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