Tab: The portion of an asphalt shingle that is outlined by the cutouts. Gives the appearance of an individual shingle after installation.

Tapered Edge Strip: Tapered insulation strip used to ease transitions from one substrate elevation to another and to provide slope along roof perimeters.

Tar (ASTM DEFINITION): A brown or black bituminous material, liquid or semi-solid in consistency, in which the predominating constituents are bitumens obtained as condensates in the processing of coal, petroleum, oil-shale, wood, or other organic materials.

Tar Boil: A small bubble found in the flood coat of an aggregate-surfaced built-up roof; usually the result of trapped moisture vapor. Tar Boils are also known as blueberries or blackberries.

Tear-Off: To remove a roof system down to the structural substrate.

Tear Resistance: A material’s ability to withstand tearing.

Tear Strength: The degree of force necessary to tear a material.

Tensile Strength: The amount of longitudinal pulling stress that a material can withstand before being pulled apart.

Termination: The sealed edges of a roof membrane.

Termination Bar: A bar, usually metal or vinyl, used to seal and anchor the free edges of a roof membrane.

Terne: An alloy composed of three or four parts of lead to one part of tin. Sometimes used to coat metal used in roof applications.

Terra Cotta: A semifired ceramic clay used in building construction.

Test Cut: A sample of the roof membrane that is removed from the roof for the purpose of determining the composition and condition of the roof assembly.

Thatch Roof: A roof covering made with straw, palms, reeds or other natural growths that are bound together in order to shed water.

Thermal Conductance (C): A unit of heat flow that is used for specific thicknesses of material or for materials of combination construction, such as laminated insulation.

Thermal Conductivity (k): The heat energy that will be transmitted by conduction through 1 square foot of 1inch thick homogeneous material in 1 hour when there is a difference of 1 degree Fahrenheit perpendicularly across the two surfaces of the material.

Thermal Insulation: A material used to reduce heat flow.

Thermal Movement: Movement of a material resulting from temperature changes.

Thermal Resistance (R): The measure of a material’s ability to resist heat flow. The formula for Thermal Resistance is R = L / k where (L) is the material’s thickness and (k) is the material’s Thermal Conductivity constant. The higher a material’s R-value, the better it insulates, and conversely.

Thermal Shock: The stresses imposed by expansion and contraction which are the result of sudden extreme temperature changes. Thermal Shock might occur, for example, when a cold rain shower suddenly cools a roof during a hot day.

Thermal Stress: Stress to a roof system or component caused by expansion and / or contraction from temperature change.

Thermoplastic: (1) adjective Becoming soft when heated and hard when cooled. (2)noun A thermoplastic resin, such as polystyrene or polyethylene.

Thermoset: A material that cannot be reshaped or formed by heating. EPDM and Butyl Rubber are thermosets.

Thinners: Liquids that are used to reduce a material’s viscosity when mixed but that evaporates during cure.

Throat: (1) The cutout of a shingle. (2) The narrowing passage located between a fireplace and smoke chamber or flue.

Through-Wall Flashing: A material that extends through a wall and is used to direct water entering a wall cavity to the exterior of the structure.

Tie-In: The joining of two different roof systems.

TIMA: Thermal Insulation Manufacturers Association

Toggle Bolt: A bolt with a separate toggle end that can be flattened to fit through a pre-drilled hole and that springs outward to provide securement when the bolt is tightened. 

Tongue and Groove: Premanufactured materials with a convex "tongue" on one side and a concave "groove" on the other so adjacent sections of material can be joined together by placing the tongue of one piece into the groove of the next, so that the pieces fit securely together.

Torque: Force applied to an object, particularly, to screw a mechanical fastener into a roof deck or substrate.

TPA: Tri-Polymer Alloy.

TPO: Thermoplastic Polyolefin compound of ethylene and propylene. Used as an elastomeric single ply roof membrane.

Transverse Seam: The joint between the top of one metal roof panel and the bottom of the next panel, which runs perpendicular to the roof slope.

Tuck Pointing: To remove old and deteriorated mortar from between masonry blocks and replace it with new mortar.


U-Value: The overall coefficient of heat transfer of an assembly measured in BTUs per square foot, per degrees Fahrenheit difference in temperature per hour.

UBC: Uniform Building Code.

UL: Underwriters Laboratories, Inc.

UL Label: A label that has been stamped on certain materials by authority of Underwriters Laboratories, Inc. indicating that the material has met certain performance criteria.

Ultraviolet Light (UV): A form of luminous energy occupying a position in the spectrum of sunlight beyond the violet, and having wavelengths that do not enter the visible spectrum. UV rays accelerate deterioration of roof materials. Hence, the need for protective coatings.

Underlayment: A material installed over the roof deck prior to the application of the primary roof covering. Usually consists of fifteen (15#) or thirty (30#) pound organic felt but can also be self-adhering such as an ice and water protection membrane.

Underwriters Laboratories (UL): A non-profit agency which functions as the testing arm of the National Board of Fire Underwriters. It maintains laboratories for the examination and testing of various devices, systems, and materials to determine their safety against the hazards of fire, wind, and accidents.

Upside Down Roof: Slang for a Protected Membrane Roof Assembly.


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