Tack-free—A film is considered tack-free when the finger, with a slight pressure, will not leave a mark. The surface will not be sticky.

Tapered edge strip—A tapered insulation strip used to elevate the roofing at the perimeter and at penetrations of the roof.

Tapered member—Abuilt-upplatememberconsistingofflanges welded to a variable depth web.

Tar boils—Bubbles of moisture vapor encased in a thin film of bitumen, also known as blueberry, blackberry, etc.

Tear strength—The maximum force required to tear a specified specimen, the force acting substantially parallel to the major axis of the test specimen. Measured in both initiated and uninitiated modes. Obtained value is dependent on specimen geometry, rate of extension, and type of fabric reinforcement. Values are reported in stress, e.g., pounds, or stress per unit of thickness, e.g., pounds per inch.

Tearoff—Removal of a failed roof system down to the structural deck surface.

Tensile strength—(1) The maximum tensile stress per unit of original cross sectional area applied during stretching of a specimen to break; units: Si-metric—Megapascal or kilopascal, customary—pound per square inch; (2) The longitudinal pulling stress a material can bear without tearing apart; (3) The ratio of maximum load to original cross-sectional area. Also called ultimate strength.

Tensile test—A test in which a specimen is subjected to increasing longitudinal pulling stress until fracture occurs.

Therm—A unit of heat commonly used by utilities quoting prices or costs. It is equivalent to 100,000 BTU.

Thermal block—A spacer of low thermal conductance material, designed to prevent formation of a thermal bridge.

Thermal bridge—Interruption of a layer of thermal insulation by a material of high thermal conductivity (e.g., metal).

Thermal conductance (C)—The rate of heat flow, in BTU's per hour, through a square foot of material or a combination of materials whose surfaces have a temperature differential of 1 °F.

Thermal conductivity (K)—The rate of heat flow, in BTU's per hour, through a square foot of material exactly one inch thick whose surfaces have a temperature differential of 1°F.

Thermal image—A visual representation of temperature distribution over a surface area. An image on a TV-like display presenting the response to infrared light waves.

Thermal insulation—A material applied to reduce the flow of heat.

Thermal resistance (R)—Resistance to heat flow. The reciprocal of conductance (C).

Thermal shock—The stress-producing phenomenon resulting from sudden temperature drops in a roof membrane when, for example, a rain shower follows brilliant sunshine.

Thermalization of fast neutrons—The process of reducing the energy of a neutron to a level where it is in equilibrium with its environment. Generally, thermal neutrons have energy levels in the 0.01 to 0.3 electron volts range. Thermalization occurs when the energy of fast neutrons is partially absorbed by moderators or hydrogen atom collisions.

Thermogram—A visible light record of the display of an infrared camera system via a Polaroid print, 35 mm film, or video tape.

Thermography—A technique for producing heat pictures from the invisible radiant energy emitted from stationary or moving objects at any distance and without in any way influencing the temperature of the objects under view. The electronic generation and display of a visible image of an infrared spectrum.

Thermoplastic—Capable of being repeatedly softened by increase of temperature and hardened by decrease in temperature. The thermoplastic form allows for easier seaming both in the factory and in the field.

Thermoplastic elastomers—Polymers capable of remelt, but exhibiting elastomeric properties; related to elasticized polyole-fins. They have a limited upper temperature service range.

Thermoplastic resin—A material with a linear macromolecular structure that will repeatedly soften when heated and harden when cooled.

Thermoset—A material that will undergo or has undergone a chemical reaction by the action of heat, catalysts, ultraviolet light, etc., leading to a relatively infusible state.

Thread count—The number of threads per inch in each direction with the warp mentioned first and the fill second, e.g. a thread count of 20 x 10 means 20 threads per inch in the warp and 10 threads per inch in the fill direction.

Through-wall flashing—A water-resistant membrane or material assembly extending totally through a wall and its cavities, positioned to direct any water within the wall to the exterior.

Throwing power—The ability of a plating solution to produce an approach to uniform metal distribution on an irregularly shaped cathode. It is measured by the percentage improvement of the metal distribution ratio over the primary current ratio.

Tie—A structural member that is loaded in tension.

Time value of money—The time-dependent value of money stemming both from changes in the purchasing power of money (that is, inflation or deflation), and from the real earning potential of alternative investments over time.

Time, drying—The period of time during which an adhesive on an adhered or an assembly is allowed to dry with or without the application of heat or pressure, or both.

Toggle bolt—A two-piece assembly consisting of a threaded bolt and an expanding clip which can fit through a drilled bolt hole, then spring outward to provide anchorage from the blind side.

Top coat—Follows prime coat application in coil coating process.

Torque wrench—A wrench containing an adjustable mechanism for measuring and controlling the amount of torque or turning force to be exerted—often used in tightening nuts or bolts.

Tributary area—The area which contributes load to a specific structural component.

Trim—The light gauge metal used in the finish of a building, especially around openings and at intersections of surfaces. Often referred to as flashing.

Truss—A structure made up of three or more members, with each member designed to carry a tension or compression force. The entire structure in turn acts as a beam.

Tuck pointing—The filling in with fresh mortar of cutout or defective mortar joints in masonry.

TV compatible—An infrared camera system whose frame rate and line frequency is compatible with closed-circuit TV systems.