This glossary contains many useful terms and definitions that will help you understand much of the work we do at ROOFCORP.

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Tab: the exposed portion of strip shingles defined by cutouts.

Tack-free time: in SPF-based roofing, a curing phase of polyurethane foam to when the material is no longer sticky. When the polyurethane foam is tack free, it can be sprayed over with another pass, referred to as a “lift”. With some care the polyurethane foam can be walked on soon after it is tack free.

Talc: whitish powder applied at the factory to the surface of some roofing materials (e.g., vulcanized EPDM membranes), used as a release agent to prevent adhesion of the membrane to itself.

Tapered edge strip: a tapered insulation strip used to (1) elevate and slope the roof at the perimeter and at curbs, and (2) provide a gradual transition from one layer of insulation to another.

Taping: (1) the technique of connecting joints between insulation boards or deck panels with tape; (2) the technique of using self-adhering tape-like materials to seam or splice single-ply membranes.

Tar: 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 boils: bubbles of moisture vapor encased in a thin film of bitumen, also known as “blackberries.”

Tarred felt: see Coal tar felt.

Tear-off and reroof: the removal of all roof system components down to the structural deck, followed by installation of a completely new roof system. Tear resistance: the load required to tear a material, when the stress is concentrated on a small area of the material by the introduction of a prescribed flaw or notch. Expressed in psi (pounds force) per inch width or kN/m (kilo-newton per meter width).

Tear strength: the maximum force required to tear a specimen. Tensile strength: the strength of a material under tension as distinct from torsion, compression or shear.

Tension leveling: the process of pulling metal coil stock between two spools under a certain pressure to help re-duce side camber and potential oil canning in the coil stock caused by manufacturing and cutting processes.

Termination: the treatment or method of anchoring and/or sealing the free edges of the membrane in a roofing or waterproofing system.

Terne: an alloy of lead and tin, used to coat sheets of carbon steel or stainless steel for use as metal roofing sheet.

Terra cotta: low-fired clay, either glazed or unglazed.

Test cut: a sample of the roof system or assembly which exposes the roof deck and is used to diagnose the condition of the membrane, evaluate the type and number of plies or number of membranes, or rates of application (e.g., the weight of the average interply bitumen moppings).

Thermal block: a compression-resistant insulation block installed between structural steel roof panels and their supporting members to help maintain insulation R-values and reduce condensation.

Thermal bridge: the penetration of a material of high thermal conductivity (e.g., a metal insulation or roof membrane fastener) through a material of low thermal conductivity (e.g., thermal insulation); the result is a lowered thermal resistance for the assembly.

Thermal cycling: sequence of values caused by a repetitive temperature differential due to changes in radiant energy.

Thermal conductance (C): the time rate of heat flow through a unit area of a body induced by a unit temperature difference between bodies. In English (inch-pound) units of measurement, the number of BTUs that pass through a specified thickness of a one square foot (0.09 m2) sample of material in one hour with a temperature difference between the two surfaces of 1° F. In English (inch-pound) units it is expressed as Btu/h·ft 2·F.
Note 1: A thermal conductance (C) value applies to a specific thickness of a specific material.
Note 2: It is mathematically incorrect to multiply or divide the thermal conductance (C) value for a specific thick-ness of a material to determine the thermal conductance value of a different thickness of the same material.
Note 3: It is mathematically incorrect to add thermal conductance (C) values to determine overall thermal performance. If it is necessary to determine the overall thermal performance of a construction, it is appropriate to convert the individual thermal conductance (C) values to thermal resistance (R) values (i.e., R= 1/c), and then add the thermal resistance values (i.e., RT=R1, + R2 + ...).

Thermal conductivity (k): the time rate of heat flow through a unit area of a homogeneous material in a direction perpendicular to isothermal planes induced by a unit temperature gradient is called thermal conductivity (k or k-value). In English (inch-pound) units of measurement, it is the number of BTUs that pass through a 1 inch (25 mm) thickness of a 1 square foot (0.09 m2) sample of material in one hour with a temperature difference between the two surfaces of 1°F. In English (inch-pound) units it is expressed as Btu·inch/h·ft2·°F.
Note 1: A thermal conductivity (k) value applies to 1 inch (25 mm) thickness of a specific material.
Note 2: It is mathematically incorrect to add, multiply, or divide the thermal conductivity (k) value of a material to determine the thermal performance value of a different thickness of the same material. If it is necessary to determine the thermal performance of a specific thickness of a material, it is appropriate to convert the thermal conductivity (k) of the material to a thermal resistance (R) value (i.e., R = 1/k), and then perform the mathematical calculation.

Thermal expansion: the increase in the dimension or volume of a body due to temperature variations.

Thermal insulation: a material applied to reduce the flow of heat.

Thermal movement: changes in dimension of a material as a result of temperature changes.

Thermal resistance (R): under steady conditions, thermal resistance is the mean temperature difference between two defined surfaces of material or construction that induces unit heat flow through a unit area. In English (inch·pound) units it is expressed as °F·ft2·h/Btu.
Note 1: A thermal resistance (R) value applies to a specific thickness of a material or construction.
Note 2: The thermal resistance (R) of a material is the reciprocal of the thermal conductance (C) of the same material (i.e., R = 1/C).
Note 3: Thermal resistance (R) values can be added, subtracted, multiplied, and divided by mathematically appropriate methods.

Thermal shock: the stress-producing phenomenon resulting from sudden temperature changes in a roof membrane when, for example, a cold rain shower follows brilliant sunshine.

Thermal stress: stress introduced by uniform or non-uniform temperature change in a structure or material that is contained against expansion or contraction.

Thermal transmittance (U or U-factor): thermal transmittance (U or U-factor) is the time rate of heat flow per unit area under steady conditions from the fluid (e.g., air) on the warm side of a barrier to the fluid (e.g., air) on the cold side, per unit temperature difference between the fluids. In English (inch·pound) units expressed as Btu/h·ft 2·°F.
Note 1: A thermal transmittance (U) value applies to the overall thermal performance of a system (e.g., roof assembly).
Note 2: Thermal transmittance (U) is sometimes called the overall coefficient of heat transfer.
Note 3: Thermal transmittance (U) is reciprocal of the overall thermal resistance (RT) of a system (i.e., U = 1/RT).

Thermography, Infrared: see Infrared thermography.

Thermoplastic: a material that softens when heated and hardens when cooled. This process can be repeated provided that the material is not heated above the point at which decomposition occurs.

Thermoplastic olefin membrane (TPO): a blend of polypropylene and ethylene-propylene polymers. Colorant, flame retardants, UV absorbers, and other proprietary substances which may be blended with the TPO to achieve the desired physical properties. The membrane may or may not be reinforced.

Thermoset: a class of polymers that, when cured using heat, chemical, or other means, changes into a substantially infusible and insoluble material.

Thinner: (1) a volatile liquid added to an adhesive or coating material to modify the consistency or other properties; (2) a liquid used to clean equipment or other surfaces.

Thixotropic: the property of a material that enables it to stiffen in a relatively short time on standing, but upon agitation or manipulation to change to a very soft consistency or to a fluid of high viscosity, the process being completely reversible.

Through-wall flashing: a water-resistant membrane or material assembly extending totally through a wall and its cavities, positioned to direct water within the wall to the exterior, usually through weep holes.

Tie-in: in roofing and waterproofing, the transitional seal used to terminate a roofing or waterproofing application at the top or bottom of flashings or by forming a watertight seal with the substrate, membrane, or adjacent roofing or waterproofing system.

T-joint: the condition created by the overlapping intersection of three or four sheets in the membrane.

Toggle bolt: a bolt having a nut with pivoted, flanged wings that close against a spring when it is pushed through a hole, and open after emerging from the hole; used to fasten objects to a hollow wall or to a wall which is accessible only from one side.

Tongue and groove planks: one of the oldest types of dimensional structural wood used as roof decking. The sides are cut with convex and concave grooves so adjacent planks may join in alignment with each other to form a uniform roof deck.

Torch-applied: method used in the installation of polymer modified bitumen membranes characterized by using open flame propane torch equipment.

TPO: thermoplastic olefin. Traffic bearing: in waterproofing, a membrane formulated to withstand a predetermined amount of pedestrian or vehicular traffic with separate protection and a wear course.

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.

Treebark surface texture: in SPF roofing, the surface condition of the foam which shows a coarse texture where valleys form sharp angles. This surface is unacceptable for proper coating and protection.

Tuckpointing: the process of removing deteriorated mortar from an existing masonry joint and troweling new mortar or other filler into the joint.