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 (Chloroflourocarbon) 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.

Heat loss Heat that is lost from a building through air leakage, conduction and radiation. To maintain a steady interior temperature, heat losses must be offset by a combination of heat gains and heat contributed by a heating system.

Heat recovery ventilation system A mechanical ventilation system that recovers energy from exhausted indoor air and transfers it to incoming air. This system usually incorporates an air-to-air heat exchanger which transfers the heat from exhaust air to the incoming air or vice versa.

HCFC (Hydrochlorofluorocarbons) are compounds containing carbon, hydrogen, chlorine and fluorine. They have shorter atmospheric lifetimes than CFCs and deliver less reactive chlorine to the stratosphere where the "ozone layer" is found.

Humidistat A humidity sensitive control device that signals the ventilation system to operate if the humidity goes above a preset limit.

Hydrophobic Having no affinity for water; not compatible with water. "Water fearing"

Infiltration Uncontrolled leakage of air into a building through cracks around doors, windows, electrical outlets and at structural joints.

Insulation Materials with low thermal conductivity characteristics that are used to slow the transfer of heat.

Isocyanate (MDI) One of a group of neutral derivatives of primary amines (R-N="C=O)" groups. An essential component (A) of spray foam chemistry.

Kilowatt-hour (kWh) Standard unit for measuring electrical energy consumption-kilowatts X hours.

Material Safety Data Sheet (MSDS) A standard formatted information sheet, prepared by a material manufacturer, describing the potential hazards, physical properties, and procedures for safe use of a material.

Mold Fungal growths often resulting in deterioration of organic materials, especially under damp conditions.

Organic Compounds containing carbon.

Overspray (1) Airborne spray loss of polyurethane foam. (2) Undesirable depositions of airborne spray loss.

Perm A unit of water vapor transmission defined as 1 grain of water vapor per square foot per hour per inch of mercury pressure difference (1 inch mercury = 0.49 psi). Metric unit of measure is ng/m2 s Pa. 1 perm = 55 ng/m2 s Pa

Permeability The time rate of water vapor transmission through unit area of a material of unit thickness induced by unit vapor pressure difference between two specific surfaces, under specified temperature and humidity conditions.

pH A measure of acidity/alkalinity of aqueous mixtures. A measure of pH 7 is neutral, lower is more acidic, higher is more alkaline.

PSI Pounds per square inch.

Radiation Transfer of energy (heat/sound) from one object to another through an intermediate space. Only the object receiving the radiation, not the space is heated. The heat is in the form of low frequency, infrared, invisible, light energy, transferring from a "warm" object to a "cold" object. It is known as the "black body effect".

Relative Humidity The ratio expressed as a percentage of the amount of moisture air actually contains to the maximum amount it could contain at that temperature.

R A unit of measurement of resistance to heat flow in hr. ft2 ° F/BTU.in.

RSI A unit of measurement of resistance to heat flow in m2 ° C/W per 25 mm. R = 0.176 RSI

Retrofit The modification of an existing building or facility to include new systems or components.

Standard Testing Laboratory test methodology for determining relative properties of materials at specific conditions.

Thermostat Temperature sensitive control device that signals a heating or cooling system to operate if the temperature in the building reaches a preset limit.

Thermal Barrier A material applied over insulation, to slow the temperature rise of the foam during a fire so as to delay its involvement in the fire.

Thermal Bridge A thermally conductive material which penetrates or bypasses an insulation system; such as a metal fastener or stud.

Thermal Resistance (R) A reaction to rapid changes in temperature.