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| Valley | The internal intersection of two sloping roof planes that runs from the eaves to the ridge. This intersection collects the most water run-off. See Open Valley, Closed-Cut Valley, and Woven Valley. |
| Vapor Migration | The natural movement of water vapor from regions of higher vapor pressure to regions of lower vapor pressure. |
| Vapor Pressure | The pressure at which a liquid and its vapor are in equilibrium at a definite temperature. |
| Vapor Retarder | A material used to restrict the passage of water vapor through a roof assembly. |
| Veneer | Any of the thin layers of wood glued together to make plywood. |
| Vent | An opening or device used to permit air or vapors to exit an enclosed structure. |
| Vent Pipe | A vertical pipe of relatively small dimensions which protrudes through a roof to provide for the ventilation of gasses. |
| Ventilation Short Circuit | The disruption of air flow in an intake-exhaust ventilation system. For instance, if vents such as turbine vents or gable vents are placed in between the intake vents and exhaust vents (such as soffit and ridge vents) then the draw created by the Stack Effect will be disrupted and the ventilation system will be much less effective. |
| Ventilator | A device that circulates fresh air and expels stale air. |
| Verge of Popcorn Texture | A rough surface texture of Sprayed Polyurethane Foam generally considered unsuitable to receive a base coating. Nodules on this surface are larger than the valleys and an additional 50% or more of coating material is necessary to properly cover and protect the surface. |
| Vermiculite | One off a group of micaceous hydrated silicate minerals related to the chlorites and used in lightweight insulating concrete. |
| Viscosity | The resistance of a material to heat flow. |
| Viscous | Having a fairly high resistance to heat flow. |
| Void | An open space or a break in continuity; a gap. |
| Volatile | That which readily vaporizes; evaporates quickly. |
| Vulcanize | To improve the strength, resiliency, and freedom from stickiness and odor of rubber, for example, by combining with sulfur or other additives in the presence of heat and pressure. |