Glossary of Commercial Roofing Terms
Click on a letter, to view the terms below.
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Thermal Resistance: an index of material applied to reduce the flow of heat.
Thermal Shock: the stress producing phenomenon resulting from sudden temperature changes in a roof membrane. (For example, when a rain shower follows brilliant, hot sunshine.)
Thermoplastic: materials that soften when heated and harden when cooled.
Thermoplastic Olefin Membrane (TPO): a blend of polypropylene and ethylene-propylene polymers. Colorant, flame retarants, UV absorbers, and other proprietary substances, which may be blended with the TPO to achieve the desired physical properties.
Thermoset: a material that solidifies or "sets" irreversibly when heated. This property is usually associated with cross-linking of the molecules induced by heat or radiation.
Through Wall Flashing: a water resistant membrane or material assembly extending through a wall and its cavities, positioned to direct any water entering the top of the wall exterior.
Tie-Off: a seal used to terminate a roofing application at to the adjacent roofing system.
TPO: see Thermoplastic Olefin Membrane.
Tuckpointing: process of removing deteriorated mortar from an existing masonry joint and troweling new mortar or other filler into the joint.
Underwriters Laboratories: an organization that classifies roof assemblies for their fire characteristics and wind uplift resistance for insurance companies in the United States.
Vapor Migration: the movement of water vapor from a region of high vapor pressure to a region of lower vapor pressure.
Vapor pressure Gradient: a graph, analogous to a temperature gradient, indicating the changes in water vapor pressure at various cross sectional planes through a roof or wall system.
Vapor Retarder: a material designed to restrict the passage of water vapor through a wall or roof. In the roofing industry, a vapor retarder should have a perm rating of 0.5 or less.
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