Air Changes per Hour (ACH). An expression of ventilation rates – the number of times in an hour that a home’s entire air volume is exchanged with outside air.
Air barrier. A layer of material resistant to air flow usually in the form of polyolefin (i.e. Typar®, Tyvek®, and other house wraps). A material which is applied in conjunction with a building component (such as a wall, ceiling or sill plate) to prevent the movement of air through that component.
Air barrier system. The assembly of components used in building construction to create a plane of air tightness throughout the building envelope and to control air leakage.
Blower Door. Diagnostic equipment consisting of a fan, removable panel and gauges, used to measure and locate air leaks.
Blowing agent. A gas or a substance capable of producing a gas used in making foamed materials.
BTU British Thermal Unit. The amount of energy that is required to raise 1 lb. of water up 1° F
BTUH. A rate of energy transfer – can be expressed as BTUs/hour
Building Envelope. The external elements walls, floor, ceiling, roof, windows and doors of a building that encloses conditioned space; the building shell.
Capillary Action, Capillarity. The movement of liquid within a material against gravity as a result of surface tension.
CFC (Chlorofluorocarbon). Any of various halocarbon compounds consisting of carbon, hydrogen, chlorine, and fluorine, once used widely as aerosol propellants and refrigerants. Chlorofluorocarbons are believed to cause depletion of the atmospheric ozone layer.
Combustion efficiency. A measure of useful heat extracted from a fuel source by an operating heating appliance. For example a furnace with a combustion efficiency of 60% converts 60% of the fuel’s energy content into useful heat. The rest is lost as exhaust gases.
Conduction. Transmission of energy (heat/sound) through a material or from one material to another by direct contact. Materials with low rates of conductive heat transfer make good insulation.
Convection. Transmission of energy (heat/sound) from one place to another by movement of a fluid such as air or water.
Density. Determined by the weight expressed in pounds of a cubic foot of spray foam.
Dew Point. The temperature at which a vapor begins to condense.
Diffusion. The movement of water vapor from regions of high relative humidity (RH) toward regions of lower RH driven by a higher to lower temperature differential.
Exfiltration. Uncontrolled leakage of conditioned air from inside the home to the outside.
Flame Retardant. A substance, which is added to a polymer formulation to reduce or retard the tendency to burn.
Flame Retarded (Adj.) The property of a material to which flame-retardant has been added.
Flame Spread. Standard test for determining relative combustibility. The flame spread of a tested material is rated relative to red oak (flame spread = 100).
Flammability. Relative ability of a material to support combustion as expressed by its flash point.