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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 (FMR)
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 larger sheets/panels.

Fading
any lightening of initial color.

Fallback
a reduction in the softening point, sometimes caused by refluxing or overheating in a relatively closed container. (see Softening Point Drift.)

Fascia
(1) in steep-slope roofing, a board that is nailed to the ends of a roof rafter; sometimes supports a gutter; (2) in a low-slope roofing, the 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.

Fastener
any of a wide variety of mechanical securement devices and assemblies, including nails, staples, 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 machine (Felt Layer)
a mechanical device used for applying bitumen and roofing felt or ply sheet simultaneously.

Felt
a flexible sheet manufactured by the interlocking of fibers with a binder or through a combination of mechanical work, mositure and heat. Felts are manufactured principally from wood pulp and vegetable fibers (organic felts), asbestos fibers (asbestos felts), glass fibers (glass fiber felts or ply sheets), or polyester fibers.

Ferrule
a metal sleeve placed inside a gutter at the top. A spike or screw is nailed/screwed through the gutter face and ferrule 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 degree angle at the base of a vertical flashing.

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).

Film
sheeting having a nominal thickness not greater than 10 mils (0.25 mm).

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 property of a material or assembly to withstand fire or give protection from it.

Fire retardant treated (FRT) plywood
plywood which has been impregnated, under pressure, with mineral salts; in the event of fire, the burning wood and salts emit noncombustible gases and water vapor instead of the usual flammable vapors.

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
in protective coatings, the detachment of small pieces of the coating film.

Flame retardant
a chemical used to impart flame resistance.

Flame spread
a propagation of a flame away from its source of ignition.

Flammability
those characteristics of a material that pertain to its relative ease of ignition and ability to sustain combustion.

Flange
the projecting edge of a rigid or semi-rigid component, such as a metal edge flashing flange.

Flash point
the lowest temperature at which vapors above a volatile combustible substance ignite in air when exposed to a flame.

Flashing cement
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 indicate 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.

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.

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, sometimes 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.

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

Fluid-applied elastomer
a liquid elastomeric material that cures after application to form a continuous waterproofing membrane.

Fly-in
method of application for roll materials by which the dry sheet is set into the bitumen or adhesive applied to the roof surface.

FM
see Factory Mutual Research (FMR).

Foam stop
the roof edge treatment upon which SPF is terminated.

Force
a strength or energy exerted or brought to bear; cause of motion or change.

FPL
Forest Products Laboratory.

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 froth packs are available to do small repairs for sprayed polyurethane foam-based roofs.