Glossary of Roofing Terms

  Fabric: a woven cloth or material of organic or inorganic filaments, threads, or yarns used for reinforcement in certain membranes and flashings.

Factory Mutual Research Corporation (FMRC): (commonly referred to as "FM") a research and testing organization that classifies roofing components and assemblies for their fire, traffic, impact (hail), weathering, and wind-uplift resistance for four major insurance companies in the United States.

Factory Seam: a splice/seam made by the manufacturer during the assembly of sections of materials into large sheets.

Fading: any lightening of initial color.

Fallback: a reduction in the softening point temperature of asphalt that occurs when asphalt is heated for prolonged periods at elevated temperature. (See Softening Point Drift.)

Fascia: a vertical or steeply sloped roof or trim located at the perimeter of a building. Typically, it is a border for the low-slope roof system that waterproofs the interior portions of the building.

Fasteners: any of a wide variety of mechanical securement devices and assemblies, including nails, screws, cleats, clips, and bolts, which may be used to secure various components of a roof assembly.

Feathering Strips: tapered wood filler strips placed along the butt ends of old wood shingles to create a relatively smooth surface when reroofing over existing wood shingle roofs. Referred to in some regions of the country as "horse feathers" or leveling strips.

Felt: a flexible sheet manufactured by the interlocking of fibers through a combination of mechanical work, moisture, and heat. Roofing felts may be manufactured principally from wood pulp and vegetable fibers (organic felts), asbestos fibers (asbestos felts), glass fibers Fiberglass felts or ply sheet), or polyester fibers.

Felt Machine (Felt Layer): a mechanical device used for applying bitumen and roofing felt or ply sheet simultaneously.

Ferrule: a small metal sleeve placed inside a gutter at the top. A spike is nailed through the gutter into the fascia board to hold the gutter in place. The ferrule acts as a spacer in the gutter to maintain its original shape.

Fiberglass Insulation: blanket or rigid board insulation, composed of glass fibers bound together with a binder, faced or unfaced, used to insulate roofs and walls. Rigid boards usually have an asphalt and kraft paper facer.

Field of the Roof: the central or main portion of a roof, excluding the perimeter and flashing.

Field Seam: a splice or seam made in the field (not factory) where overlapping sheets are joined together using an adhesive, splicing tape, or heat- or solvent-welding.

Filler: a relatively inert ingredient added to modify physical characteristics.

Fillet: a heavy bead of waterproofing compound or sealant material generally installed at the point where vertical and horizontal surfaces meet; the desired effect to take out the 90° angle at the base of a vertical flashing.

Film: a membrane or sheeting having nominal thickness not greater than 10 mils.

Film Thickness: the thickness of a membrane or coating. Wet film thickness is the thickness of a coating as applied; dry film thickness is the thickness after curing. Film thickness is usually expressed in mils (thousandths of an inch).

Fin: a term used to describe a deck surface condition. A sharp raised edge (generally in concrete) capable of damaging a roof membrane or vapor retarder.

Fine Mineral-Surfacing: water-insoluble, inorganic material, more than 50 percent of which passes through a No. 35 sieve. Used on the surface of various roofing materials and membranes to prevent sticking.

Fire Resistance: the ability of a building component to act as a barrier to the spread of fire and confine it to the area of origin.

Fishmouth: (also referred to as an Edge Wrinkle) (1) a half-cylindrical or half-conical shaped opening or void in a lapped edge or seam, usually caused by wrinkling or shifting of ply sheets during installation; (2) in shingles, a half-conical opening formed at a cut edge.

Flaking: detachment of a uniform layer of a coating or surface material, usually related to internal movement, lack of adhesion, or passage of moisture.

Flame Retardant: a substance which is added to a polymer formulation to reduce or retard its tendency to burn.

Flame Spread: Per ASTM E 84, a measure of relative combustibility. The flame spread of a tested material is rated relative to asbestos cement board Flame spread = 0) and red oak flooring Flame spread = 100).

Flammability: the characteristics of a material to burn or support combustion.

Flange: the projecting edge of a rigid or semi-rigid component, such as a metal edge flashing flange, skylight flange, flashing boot, structural member, etc.

Flash Point: the lowest temperature of a liquid at which it gives off vapors sufficient to form an ignitable mixture with air near its surface.

Flashing: components used to weatherproof or seal the roof system edges at perimeters, penetrations, walls, expansion joints, valley, drains, and other places where the roof covering is interrupted or terminated. For example, membrane base flashing covers the edge of the field membrane, and cap flashings or counterflashings shield the upper edges of the base flashing.

Flashing Cement: as used by the roofing industry, an ASTM D 2822 Type II roof cement that is a trowelable mixture of solvent-based bitumen and mineral stabilizers that may include asbestos or other inorganic or organic fibers. Generally, flashing cement is characterized as vertical-grade, which indicates it is intended for use on vertical surfaces. (See Asphalt Roof Cement and Plastic Cement.)

Flashing Collar: (sometimes referred to as a Roof Jack or Flashing Boot) an accessory flashing used to cover and/or seal soil pipe vents and other penetrations through the roof.

Flat Lock: a method of interlocking metal panels in which one panel edge is folded back on top of itself and the other panel is folded under, after which the two panels are hooked together.

Fleece: mats or felts composed of fibers (usually non-woven polyester fibers), often used as a membrane backer.

Flood (Pour) Coat: the surfacing layer of bitumen into which surfacing aggregate is embedded on an aggregate-surfaced built-up roof. A flood coat is generally thicker and heavier than a glaze coat, and is applied at approximately 45-60 pounds per square (2-3 kilograms per meter).

Flood Test: the procedure where a controlled amount of water is temporarily retained over a horizontal surface to determine the effectiveness of the waterproofing.

Fluid-Applied Elastomer: a liquid elastomeric material that cures after application to form a continuous waterproofing membrane.

FM: see Factory Mutual Research Corporation.

Force: an action that changes or tends to change the state of rest or motion.

Framed Opening: an opening in a wall or roof of a building, surrounded by structural framing, usually for field installed accessories such as skylights or ventilators.

Froth Pack: a term used to describe small, disposable aerosol cans that contain SPF components. Two component packs are available to do small repairs for sprayed polyurethane foam-based roofs.

G-90: a typical coating weight for galvanized metal sheet. Equates to 0.90 ounces (26 g) of zinc per sq. ft., measured on both sides.

Gable: a triangular portion of the endwall of a building directly under the sloping roof and above the eave line. (See Figure 10.)

Gable-Shaped Roof: a single-ridge roof that terminates at gable end(s). (See Figure 11.)

Galvalume~: trade name for a coating, used over metal, that is composed of aluminum zinc for corrosion protection.

Galvanic Action: an electroylic reaction between dissimilar metals in the presence of an electrolyte.

Galvanize: to coat with zinc.

Galvanized Steel: steel coated with zinc for corrosion resistance.

Gambrel: a roof that has two pitches on each side. (See Figure 12.)

Gauge: a measurement of rating metal thickness.

Geodesic Dome: a rounded structure made of short, straight, triangular sections that form polygons. (See Figure 13.)

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 for protection of drainage systems from clogging.

Girt: a horizontal beam that supports wall cladding between columns.

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.)

Gloss: the shine, sheen, or luster of a dried film.

Grain: a unit used to measure the mass of moisture.

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.

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.

Grout (Non-Shrink): a cementitious material used to fill pitch-pans/pockets, prior to the application of a pourable sealer.

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.

Hand-Tabbing: method of spot applying asphalt-based adhesive to shingles for securement and wind resistance.

Hardness: the relative resistance of a material to indentation.

Headlap: the distance of overlap measured from the uppermost ply or course to the point that it laps over the undermost ply or course. (See Figures 14 and 15.)

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 thermoses 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. (See Figure 16.)

Hip Roof: a roof that rises by inclined planes to form one or more hips. (See Figure 17.)

Hoist: a mechanical lifting device.

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 maximum amount that the air could contain at the same temperature.)

HVAC: heating, ventilating, and air conditioning equipment.

Hypalon~: a registered trademark of E.l. 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.

Impact Resistance: the ability of a roofing material to resist damage (e.g., puncturing) from falling objects, application equipment, foot traffic, etc. The impact resistance of the roofing assembly is a function of all of its components, not just the membrane itself.

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

Incline: the slope of a roof expressed either in percent or in the number of vertical units of rise per horizontal units of run. (See Slope.)

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.)

Inorganic: any chemical or compound that is derived from minerals, does not contain carbon, and is not classified as organic; being or composed of materials other than hydrocarbons and their derivatives; not of plant or animal origin.

Insect Screen: wire mesh used to prevent insects from entering the building through ventilators, louvers, or other openings.

Insulation: any of a variety of materials designed to reduce the flow of heat, either from or into a building. (See also 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 winddriven rain and snow. Typically used with wood shakes.

Interlocking Shingles: individual shingles that mechanically attach to each other to provide wind resistance.

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™): 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.

Isocyanate: a highly reactive organic chemical containing one or more isocyanate (-N=C=O) groups. A basic component in SPF based systems and some polyurethane coating systems.