A component that retards water vapor diffusion but does not totally prevent its transmission. Vapor retarder material is usually a thin sheet or coating. However, a construction of several materials, some perhaps of substantial thickness, could also constitute a vapor retarder system.
Glossary
The following is a compilation of building energy-code related terms and acronyms used on the Building Energy Codes website and throughout the building construction industry.
Select a letter to navigate through the glossary:
Vapor Retarder
Variable Air Volume (VAV)
HVAC system that controls the dry-bulb temperature within a space by varying the volumetric flow of heated or cooled supply air to the space.
Variable Frequency Drive
Changes the speed of the motor by changing the voltage and frequency of the electricity supplied to the motor based upon system requirements.
Vent Damper
A device intended for installation in the venting system of an individual, automatically operated, fossil-fuel-fired appliance in the outlet or downstream of the appliance draft control device, which is designed to automatically open the venting system when the appliance is in operation and to automatically close off the venting system when the appliance is in a standby or shutdown condition.
Ventilated Mechanically
The process of supplying or removing air by mechanical means to or from any space. Such air may or may not have been conditioned.
Ventilated Naturally
The process of supplying or removing air by natural means to or from any space.
Ventilation
The process of supplying or removing air by natural or mechanical means to or from any space. Such air shall be permitted to be conditioned or unconditioned.
Ventilation Air
That portion of supply air that comes from outside (outdoors) plus any recirculated air that has been treated to maintain the desired quality of air within a designated space. See ASHRAE 62 and definition of "Outdoor Air."
Vertical Fenestration
All fenestration other than skylights.
Visible Light Transmittance (VLT)
The fraction of solar radiation in the visible light spectrum that passes through the fenestration.
Voltage Drop
A decrease in voltage caused by losses in the lines connecting the power source to the load.