Term Description
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 or growth medium particles and other contaminants while allowing water to freely pass through; used to protect drainage systems from clogging.
Girt

A horizontal beam that supports wall cladding between columns.
Glass felt

Glass fibers bonded into a sheet with resin and suitable for impregnation with asphalt in the manufacture of bituminous waterproofing, roof 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.
Gloss

The shine, sheen or luster of a dried film or another surface.
Grade

(1) The term used when referring to the ground elevation around a building; (2) the classification of materials by quality or specific type.
Gradient

(1) The change in a variable quantity, as temperature or pressure per unit distance; may be represented by a curve of such a rate of change; (2) the rate of change of a variable with respect to a measured quantity.
Graduated slate roof

A slate roof system in which successive slate courses diminish in length and/or thickness from eave to peak.
Grain

A unit of measure in the English System of units equal to 1/7,000 lb.; used in measuring atmospheric water vapor content.
Granules

Opaque, natural or synthetically colored aggregate commonly used to surface cap sheets, shingles and other granule-surfaced roof coverings; also referred to as mineral or ceramic granules.
Gravel

Coarse granular aggregate, with pieces larger than sand grains, 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.
Grout

A mixture of cement, sand and water used to fill cracks and cavities in masonry.
Growth medium

A growth medium specially formulated (engineered) to provide a proper growing environment for the specific plants to be included in a vegetative roof system.
Gusset

(1) Used at the bottom of a steep-slope roof system valley, a large flat metal piece(s) wider than the valley to help prevent buildup at the base of the valley either from debris or ice-dam formations. (2) plate used to connect two or more members or to reinforce a joint.
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.
Gypsum deck

A mixture of calcined gypsum binder and wood chips or other aggregate; when mixed with water, sets to a conglomerate mass; used for poured gypsum roof decks.
Hand-tabbing

A method of spot-applying asphalt-based adhesive to shingles for securement and wind resistance. Also termed "hand-sealing."
Hardboard

Common name for asphaltic protection board used in waterproofing applications. Hardboard products may consist of a combination of asphalt-saturated organic (cellulosic) felt and coated or saturated nonwoven glass felt or may be entirely glass-felt-based; classified by ASTM D6506.
Head lap

(1) The distance of overlap measured from the uppermost ply or course to the point where it laps over the undermost ply or course; (2) the head lap area.
Heat flow

The quantity of heat transferred to or from a system in a unit of time.
Heat flux

The heat flow rate through a surface of unit area perpendicular to the direction of heat flow.

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