Roofing Terms G – I
- -G-
- G-90
- a designation for galvanized metal sheet, indicating 0.90 ounces (26 g) of zinc per square foot, measured on both sides.
- Gable
- the vertical triangular portion of the end of a building having a double-sloping roof, from the level of the eaves to the ridge of the roof.
- Gable roof
- a single-ridge roof that terminates at gable end(s).
- Galvalume
- trade name for a metal alloy coating that is composed of aluminum, zinc and silicone.
- Galvanic action
- an electrochemical action that generates electrical current between two metals of dissimilar electrode potential.
- Galvanic series
- a list of metals and alloys arranged according to their relative electrolytic potentials in a given environment.
- Galvanize
- to coat steel or iron with zinc.
- Galvanized steel
- steel coated with zinc for corrosion resistance.
- Gambrel
- a roof that has two pitches on each side, where the upper roof area has less slope than the lower roof areas.
- Gauge
- a metal thickness measurement.
- Geocomposite
- a prefabricated water drainage material used to relieve hydrostatic pressure against waterproofing and promote drainage.
- Geotextile
- a tightly woven fabric used to restrict the flow of fine soil particles and other contaminants while allowing water to pass freely through; used to protect drainage systems from clogging.
- Girt
- a horizontal beam that supports wall cladding between columns.
- Glass fiber insulation
- blanket or rigid board insulation, composed of glass fibers bound together with a binder, faced or unfaced, used to insulate roofs and walls. The NRCA Roofing and Waterproofing Manual—Fifth Edition. Glossary 987
- Glass felt
- glass fibers bonded into a sheet with resin and suitable for impregnation with asphalt in the manufacture of bituminous waterproofing, roofing membranes and shingles.
- Glass mat
- a thin mat of glass fibers with or without a binder.
- 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. (see Flood Coat.)
- Gloss
- the shine, sheen or luster of a dried film.
- Grain
- a unit of measure in the English System of units; 7,000 grains equals 1 lb.; used as a measure of the weight of moisture in air.
- 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
- coarse granular aggregate resulting from the natural erosion of rock.
- Gravel stop
- a flanged device, frequently metallic, designed to prevent loose aggregate from washing off the roof and to provide a continuous finished edge for the roofing.
- Groundwater level
- at a particular site, the level, below which the subsoil and rock masses of the earth are fully saturated with water.
- Grout
- a mixture of cement, sand, and water used to fill cracks and cavities in masonry.
- Gusset
- used at the bottom of a steep-slope roof system valley, a large flat metal piece(s) wider than the valley to help prevent build-up at the base of the valley, either from debris or ice dam formations.
- 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.
- Gypsum board panels
- cementitious board stock with noncombustible core primarily comprised of gypsum that is commonly used as a barrier board thermal barrier or cover board in a roof assembly.
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- -H-
- Hand-tabbing
- method of spot applying asphalt-based adhesive to shingles for securement and wind resistance.
- Headlap
- the distance of overlap measured from the uppermost ply or course to the point where it laps over the undermost ply or course.
- Heat flow
- the quantity of heat transferred to or from a system in a unit of time.
- Heat seaming
- the process of joining thermoplastic films, membranes, or sheets by heating and then applying pressure to bring both materials in contact with each other. (see Heat Welding.)
- 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.)
- Hem
- the edge created by folding metal back on itself.
- Hip
- the inclined external angle formed by the intersection of two sloping roof planes.
- Hip roof
- a roof that rises by inclined planes to form one or more hips.
- Hoist
- a mechanical lifting device.The NRCA Roofing and Waterproofing Manual—Fifth Edition 988 Glossary
- Holiday
- an area where a liquid-applied material is missing or absent.
- Honeycomb
- voids left in concrete resulting from failure of the mortar to effectively fill the spaces among coarse aggregate particles.
- Hot or Hot stuff
- a roofing worker’s term for hot bitumen.
- Hue
- the subjective perception of color such as red, yellow, green, blue, purple or some combination; white, black or gray possess no hue.
- Humidity
- the condition of the atmosphere with respect to water vapor. (see Relative Humidity.)
- HVAC
- heating, ventilating, and air conditioning equipment.
- Hybrid roof covering
- combination of two or more separate and distinct roof membranes; e.g., three ply smooth BUR and a modified bitumen cap.
- Hydration
- the chemical reaction by which a substance (such as Portland cement) combines with water, giving off heat to form a crystalline structure in its setting and hardening.
- Hydrocarbon
- an organic chemical compound primarily containing the elements carbon and hydrogen.
- Hydrostatic pressure
- the pressure equivalent to that exerted on a surface by a column of water of a given height.
- Hydrostatic pressure relief system
- a system of perimeter and/or under slab drains used to regulate the hydrostatic pressure in the earth surrounding a below-grade structure.
- Hygroscopic
- attracting, absorbing and retaining atmospheric moisture.
- Hypalon™
- a registered trademark of E.I. du Pont de Nemours & Co., for ”chlorosulfonated polyethylene” (CSPE). (see Chlorosulfonated Polyethylene.)
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- -I-
- ICBO
- International Conference of Building Officials.
- 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.
- Ice dam protection membrane
- a continuous membrane installed under steep slope roofing materials in areas subject to ice damming that prohibits water which gets through the roof covering from getting into the structure. Must also seal the fasteners that penetrates it.
- Ignition temperature
- the lowest temperature at which combustion will occur spontaneously under specific conditions.
- Impact resistance
- resistance to fracture under the sudden application of an exerted force.
- Impregnate
- In roofing materials manufacture, to completely surround the fibers in a felt or mat with bitumen, with the spaces between the fibers partially or completely filled without a continuous coating of bitumen on the surface.
- Infrared thermography
- The process of displaying variations of apparent temperatures (variation of temperature or emissivity or both) over the surface of an object by measuring variations in infrared radiance.
- Inorganic
- being or composed of materials other than hydrocarbons and their derivatives, or matter that is not of plant or animal origin.
- Insect screen
- wire mesh used to prevent insects from entering the building through ventilators, louvers, or other openings.
- In-service R-value
- thermal resistance value established under installed conditions and measured over the expected service life of the material. The NRCA Roofing and Waterproofing Manual—Fifth Edition Glossary 989
- Insulation
- any of a variety of materials designed to reduce the flow of heat, either from or into a building. (see Thermal Insulation.)
- Intake ventilation
- the fresh air that is drawn into a passive ventilation system through vents typically installed in the soffit or eave of a roof.
- Interlayment
- a felt, metal, or membrane sheet material used between courses of steep-slope roofing to improve the weather- and water-shedding characteristics of the primary roof covering during times of wind-driven precipitation. Typically used with wood shakes.
- Interlocking shingles
- individual shingles that mechanically attach to each other to provide enhanced wind resistance without reliance on sealing strips.
- Inverted roof membrane assembly (IRMA™)
- a patented, proprietary variation of the “protected membrane roof assembly” in which Styrofoam® brand insulation and ballast are placed over the roof membrane. IRMA™ and Styrofoam® are registered trademarks of the Dow Chemical Company.
- ISANTA
- International Staple, Nail & Tool Association
- Isocyanate
- a highly reactive organic chemical containing one or more isocyanate (-N=C=0) groups. A basic component in SPF based systems and some polyurethane coating systems.
- Isolation sheet
- refer to slip sheet.
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