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

Term used to describe moisture laden air. Vapor migration: the movement of water vapor from a region of high vapor pressure to a region of lower vapor pressure.

the pressure exerted by a vapor of a solid or liquid when in equilibrium with the liquid or solid.

a layer(s) of material or a laminate used to appreciably reduce the flow of water vapor into a roof assembly.

(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.

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

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

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.

an aggregate used in lightweight insulating concrete, formed by heating and expanding of a micaceous material.

the resistance of a material to flow under stress. For bitumen, measured in centipoise. (see Viscous.)

resistant to flow under stress. In everyday terms (and for fluids only), viscosity is "thickness" or "internal friction".

an open space or break in consistency.

a relative term expressing the tendency to form vapor. The NRCA Roofing and Waterproofing Manual—Fifth Edition 1008 Glossary

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.

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.