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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U-Value: see Thermal transmittance. UBC: Uniform Building Code.

UL: Underwriters Laboratories, Inc.

UL label: an identification label or seal affixed to a roofing product or package with the authorization of Underwriters Laboratories, Inc. The presence of the label indicates that the product has met certain performance criteria.

Ultraviolet (UV): invisible light radiation, adjacent to the violet end of the visible spectrum, with wavelengths from about 200 to 400 nm (nanometres).

Underlayment: an asphalt-saturated felt or other sheet material (may be self-adhering) installed between the roof deck and roof covering, usually used in a steep-slope roof construction. Underlayment is primarily used to separate the roof covering from the roof deck, shed water and provide secondary weather protection for the roof area of the building.

Underwriters Laboratories, Inc. (UL): an organization that tests, rates and classifies roof assemblies for their resistance to fire, impact, leakage, corrosion of metal components and wind uplift. Uplift: see Wind uplift.

Valley: the internal angle formed by the intersection of two sloping roof planes.

Vapor migration: the movement of water vapor from a region of high vapor pressure to a region of lower vapor pressure.

Vapor pressure: the pressure exerted by a vapor of a solid or liquid when in equilibrium with the liquid or solid. Vapor retarder: a layer(s) of material or a laminate used to appreciably reduce the flow of water vapor into a roof assembly.

Veneer: (1) a single wythe of masonry for facing purposes that may not be structurally connected; (2) any of the thin layers of wood glued together to form plywood.

Vent: an opening designed to convey air, heat, water vapor or gas from inside a building or a building component to the atmosphere.

Ventilator: an accessory that is designed to allow for the passage of air.

Verge of popcorn texture: in SPF roofing, the verge of popcorn surface texture is the roughest texture suitable for receiving the protective coating on a sprayed polyurethane foam roof. The surface shows a texture where nodules are larger than valleys, with the valleys relatively cured. This surface is acceptable for receiving a protective coating only because of the relatively cured valleys. However, the surface is considered undesirable because of the additional amount of coating material required to protect the surface properly.

Vermiculite: an aggregate used in lightweight insulating concrete, formed by heating and expanding of a micaceous material. Viscosity: the resistance of a material to flow under stress. For bitumen, measured in centipoise. (see Viscous.)

Viscous: resistant to flow under stress.

Void: an open space or break in consistency.

Volatile: a relative term expressing the tendency to form vapor.

Volatile organic compounds (VOC): means any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate, which participate in atmospheric photochemical reactions.

Vulcanization: an irreversible process during which a rubber compound, through a change in its chemical structure (for example, cross-linking), becomes less plastic and more resistant to swelling by organic liquids and elastic properties are conferred, improved, or extended over a greater range of temperature.