Term Description
Fiberglass base sheet

A fiberglass-reinforced base sheet for built-up roof system construction, impregnated and coated with asphalt and surfaced with mineral matter; classified by ASTM D4601 as Type I or Type II.

Fiberglass felt

See "felt."

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.

Fiberglass mat

An asphalt roofing reinforcement manufactured from glass fibers.


A relatively inert ingredient added to modify physical characteristics.


A heavy bead of waterproofing compound or sealant material generally installed at the point where vertical and horizontal surfaces meet to obtain a more gradual transition through the 90-degree angle at the base of a vertical flashing.


Sheeting having a nominal thickness not greater than 10 mils (0.010 inch).

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).

Filter fabric

A tightly woven fabric, typically polyester or polyethylene/polypropylene, used to restrict the flow of fine particles and other contaminants while allowing water to pass freely through. It is used to protect drainage systems from clogging.


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 rating

Grade based on standard testing procedures of various materials.

Fire resistance

The property of materials or their assemblies that prevents or retards the passage of excessive heat, hot gases or flames under conditions of use.

Fire-retardant-treated (FRT) plywood

Plywood that 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.


Materials used to limit the spread of fire.


(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 (also referred to as an edge wrinkle); (2) in shingles, a half-conical opening formed at a cut edge.


The actual detachment of film fragments from the previously applied coating or substrate.

Flame retardant

A chemical used to impart flame resistance.

Flame spread

The propagation of a flame away from its source of ignition.


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


Subject to easy ignition and rapid flaming combustion.


The projecting edge of a rigid or semirigid component, such as an edge metal flashing flange.

Flash point

The lowest temperature at which vapors above a combustible substance ignite in air when exposed to an ignition source.


Components used to weatherproof or seal roof and waterproofing system edges at perimeters, penetrations, walls, expansion joints, valleys, drains and other places where the roof covering or waterproofing membrane 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

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."