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 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 housewraps). 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 Btu/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 percent converts 60 percent of the fuels 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 any material.

Dew Point; The temperature at which a vapor begins to condense.

Diffusion; The movement of water vapor from regions of high relative humidity (RH) or pressure 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; Unit of measure generated by a standard test for determining relative combustibility. The flame spread of a tested material is rated relative to red oak (flame spread = 100). ASTM = E84 is the test method used to determine the above.

Flammability; Relative ability of a material to support combustion as expressed by its flash point.

Heat loss; Heat that is lost from a building by 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 halogeneted 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" Also preventing growth of mold and mildew.

Infiltration; Uncontrolled leakage of air into a building through cracks around doors, windows, electrical outlets and at structural joints. Uncontrolled leakage of conditioned air from outside of the home to the inside.

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

Isocyanate (typically MDI); One of a group of neutral derivatives of primary amines (R-N=C=O) groups. An essential component (A) of urethane 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, some 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 particle loss of polyurethane foam in spray application. (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. (add units like above)

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

Pressurized Fog Testing; Done in conjunction with a blower door test, presurized fog test visually identifies air leaks in a building’s envelope. The test is usually done when temperature and weather conditions make an infrared scan difficult.

Product Data Sheet; A listing of all the general characteristics and components of a chemical or product. (Also see MSDS).

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-Value; 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. (link to R-value table).

Resin; Component B in urethane foam chemistry. This component is mixed with the A component to form foam insulation.

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.

SUPERGREEN™ foam; is a rigid plastic urethane foam that uses zero ozone depletion Freon (HFC-134a) as the blowing agent.

Superinsulation; The word was coined during the energy crisis of the 70's it is an approach to solving thermal envelope problems. Superinsulation is usually, but not always, one of the several urethane foam systems.

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

Thermal Barrier; A material applied over insulation designed to slow the temperature rise of the foam during a fire situation and 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); An index of a material's resistance to heat flow. See R-Value and RSI.

Thermal Shock; A building materials reaction to rapid changes in temperature, usually associated with the curing process.

Thermography (Infrared Scan); A building energy diagnostic technique using an infrared camera for locating areas of temperature differential or air leakage in a building. Often used in conjunction with pressurization or depressurization.

U-Value; Overall thermal conductance. U-value is equal to the inverse of the sum of the R-values in a system (U = 1 /R total).

Vapor Retarder/Barrier; A layer of moisture resistant material usually which controls moisture diffusion (defined as less than 1 perm in typical building environments) to prevent moisture migration into building cavities.

Viscosity; The thickness or resistance to flow of a liquid. Viscosity generally decreases as temperature increases; application temperatures of urethane foam components are specified in part, to control viscosity at the dispensing gun.

Volatile Organic Compounds (VOC); Any compound containing carbon and hydrogen or containing carbon and hydrogen in combination with other elements.

Spray Foam Building Science Glossary

Here are the ABC's of building science terminology, according to Building Science Corporation. There are a lot of construction glossaries available, on and off the web. This one is unique in that it is centered on building science and uses the Builder's Guides as a primary reference and source of terms. Whenever possible, a link to the most relevant BSC web site document is provided for more detailed information on the term or concept. Stay tuned as these initial ABC's grow into a full-blown glossary of over 100 terms unique to our industry.

Air Barrier: Air barriers are systems of materials designed and constructed to control airflow between a conditioned space and an unconditioned space. The air barrier system is the primary air enclosure boundary that separates indoor (conditioned) air and outdoor (unconditioned) air. In multi-unit/townhouse/apartment construction the air barrier system also separates the conditioned air from any given unit and adjacent units. Air barrier systems also typically define the location of the pressure boundary of the building enclosure. In multi-unit/townhouse/apartment construction the air barrier system is also the fire barrier and smoke barrier in inter-unit separations. In such assemblies the air barrier system must also meet the specific fire resistance rating requirement for the given separation.

Air Barrier; Performance Requirements: Air barrier systems typically are assembled from materials incorporated in assemblies that are interconnected to create enclosures. Each of these three elements has measurable resistance to airflow. The recommended minimum resistances or air permeances for the three components are listed as follows:

Material 0.02 l/(s-m2)@75 Pa
Assembly 0.20 l/(s-m2)@75 Pa
Enclosure 2.00 l/(s-m2)@75 Pa
Air Retarder: Materials and assemblies that do not meet the performance requirements of air barrier materials and air barrier assemblies, but are nevertheless designed and constructed to control airflow are said to be air retarders.

Building Enclosure: A building enclosure is an environmental separator. It separates the interior environment from the exterior environment. A building enclosure controls heat flow, air flow, water vapor flow, rain, groundwater, light and solar radiation, noise and vibrations, contaminants, environmental hazards and odors, insects, rodents and vermin, and fire. A building enclosure provides strength and rigidity and must be durable, aesthetically pleasing and economical.

Conditioned Space: A conditioned space is the part of the building that is designed to be thermally conditioned for the comfort of occupants or for other occupancies or for other reasons.

Diffusion: The movement of individual molecules through a material. The movement occurs because of concentration gradients and thermal gradients, independent of airflow.

Drainage Plane: Drainage planes are water repellent materials (building paper, housewrap, foam insulation, etc.) which are typically located behind the cladding and are designed and constructed to drain water that passes through the cladding. They are interconnected with flashings, window and door openings, and other penetrations of the building enclosure to provide drainage of water to the exterior of the building. The materials that form the drainage plane overlap each other shingle fashion or are sealed so that water drains down and out of the assembly. The drainage plane is also referred to as the "water resistant barrier" or WRB.

Equivalent Leakage Area of a building (EqLA or ELA): Quantitative expression of the airtightness of a building enclosure. EqLA is the method set by the Canadian General Standards Board in which a blower door depressurizes the building enclosure to 10 Pascals and the leakiness of the enclosure is expressed as a summary hole in square inches. ELA is set by the ASTM equivalent procedure at a pressure differential of 4 Pascals.

Foundation, Water-managed: Systems for at or below-grade enclosure assemblies where gravity (drainage) is used to move liquid water away from the structure, relieving hydrostatic water forces.

Grade Beam: A foundation wall that is cast at or just below the grade of the earth, most often associated with the deepened perimeter concrete section in slab-on-grade foundations.

Housewrap: Any of the numerous spun-fiber polyolefin rolled sheet goods, or perforated plastic films designed to function as drainage planes.

Indoor Air: Air in a conditioned space.

Insulating Sheathing: Non-structural insulating board products with varying R-values and a wide variation in vapor permeability and drainage characteristics. Materials include expanded polystyrene (EPS), extruded polystyrene (XPS), polyisocyanurate (most often foil-faced), rigid fiberglass, and mineral wool.

Jump Duct: A flexible, short, U-shaped duct (typically 10-inch diameter) that connects a room to a common space as a pressure balancing mechanism. Jump ducts serve the same function as transfer grilles. Used when return ducts are not located in every room.

Kiln-dried Lumber: Any lumber placed in a heated chamber or "shed" to reduce its moisture content to a specified range or average under controlled conditions. For softwood framing lumber, the moisture content of KD lumber is somewhat based on regional conventions but is most often an average of 12% by weight. In comparison, the moisture content of thoroughly air-dried softwood framing lumber is 15% to 20%.

Low-E: Most often used in reference to a coating for high-performance windows, the "e" stands for emissivity or re-radiated heat flow. The thin metallic oxide coating increases the U-value of the window by reducing heat flow from a warm(er) air space to a cold(er) glazing surface. The best location for the coating is based on whether the primary heat flow you want to control is from the inside out (heating climates) or the outside in (cooling climates).

Mechanical Ventilation: Controlled, purposeful introduction of outdoor air to the conditioned space.

Outdoor Air: Air outside the building. It can enter the conditioned space via the ventilation system, or by infiltration through holes in the pressure boundary or designed ventilation openings.

Ozone: 03 instead of 02. This 3-atom molecule is an even more active oxidizing agent than its more common 2-atom relative. At ground level, ozone is a pollutant and in the upper atmosphere it is a solar shield (location, location, location). Touted for its ability to "clean" air in room or household ozone generators, this application actually does more harm than good-ozone's highly reactive nature tends to accelerate the breakdown of synthetic materials in homes such as paints, plastics, and ever-available volatile organic compounds, often with less-than-desirable results. All told, we look to protect ozone in the heavens and shun it here at home, inside and out.

Permeance: The physical property that defines the ease at which water molecules diffuse through a material. It is to vapor diffusion what conductance is to heat transfer. The unit of measurement is typically the "perm."

Pressure Boundary: Air barriers define the location of the pressure boundary of the building enclosure. See also Air Barrier.

R-value: Quantitative measure of resistance to heat flow or conductivity, the reciprocal of U-factor. The units for R-value are ft2 °F hr/Btu (English) or m2 °K hr/W (SI or metric). While many in the building community consider R-value to be the primary or paramount indicator of energy efficiency, it only deals conduction, one of three modes of heat flow, (the other two being convection and radiation). As an example of the context in to which R-value should be placed, 25% to 40% of a typical home's energy use can be attributed to air infiltration.

Thermal Boundary: The layer in a building enclosure that controls the transfer of energy (heat) between the interior and the exterior. It is a component of the building enclosure and it may, but does not have to align with the pressure boundary.

U-factor: Quantitative measure of heat flow or conductivity, the reciprocal of R-value. While building scientists will use R-values for measures of the resistance to heat flow for individual building materials, U-factor is always used as a summary measure for the conductive energy measure of building enclosures.

Vapor Barrier: A vapor barrier is a Class I vapor retarder. Vapor barriers are materials that are vapor impermeable.

Vapor Impermeable: Materials with a permeance of 0.1 perm or less (rubber membranes, polyethylene film, glass, aluminum foil)

Vapor Permeable: Materials with a permeance of greater than 10 perms (housewraps, building papers)

Vapor Retarder: A vapor retarder is the element that is designed and installed in an assembly to retard the movement of water by vapor diffusion. There are several classes of vapor retarders:

Class I vapor retarder - 0.1 perm or less
Class II vapor retarder - 1.0 perm or less and greater than 0.1 perm
Class III vapor retarder - 10 perms or less and greater than1.0 perm
The test procedure for classifying vapor retarders is ASTM E-96 Test Method A - the desiccant or dry cup method.

Vapor Semi-Impermeable: Materials with a permeance of 1.0 perm or less and greater than 0.1 perm (oil-based paints, most vinyl coverings)

Vapor Semi-Permeable: Materials with a permeance of 10 perms or less and greater than 1.0 perm (plywood, OSB, most latex-based paints)

Water Resistant Barrier: A water resistant barrier (WRB) is also referred to as a drainage plane.

Wind-Washing: The phenomenon of air movement that occurs due to wind entering building enclosures typically at the outside corners and roof eaves of buildings. Wind-washing can have significant impact on thermal and moisture movement and hence thermal and moisture performance of exterior wall assemblies.

Xeriscaping: Climate-tuned landscaping that minimizes outdoor water use while maintaining soil integrity and building aesthetics. Typically includes emphasis on native plantings, mulching, and no or limited drip/subsurface irrigation.

Zero Energy House: Any house that averages out to net zero energy consumption. A zero energy home can supply more than its needs during peak demand, typically using one or more solar energy strategies, energy storage and/or net metering. In a zero energy home, efficiencies in the building enclosure and HVAC are great enough that plug loads tend to dominate and so these homes must have the added focus of high efficiency appliances and lighting.



ABAA; Air Barrier Association of America

AIA; American Institute of Architects

AISI; American Iron & Steel Institute
ALA; American Lung Association
ANSI; American National Standards Institute
ASHRAE; American Society for Heating, Refrigeration and Air Conditioning Engineers
ASTM; American Society for Testing and Materials
BETEC; Building Environment & Thermal Envelope Council
BOCA; Building Officials and Code Administrators
CABO (ICC); Conference of American Building Officials (International Code Council)
CCMC; Canadian Construction Materials Centre
CSA; Canadian Standards Association
DOE; U.S. Department of Energy
EPA; Environmental Protection Association
EEBA; Energy Efficient Builders Association
EREC; Energy Efficiency and Renewable Energy Clearing House (DOE program)
FSEC; Florida Solar Energy Center
IBC; International Building Code
ICBO; International Conference of Building Officials
NAHB; National Association of Home Builders
NAHBRC; NAHB Research Center
NBC; National Building Code of Canada
NEAT; Novel Environmental Advanced Technology
NER; National Evaluation Report
NIBS; National Institute of Building Sciences
NIST; National Institute of Standards and Technology
NRC; National Research Council of Canada
ORNL; Oak Ridge National Laboratories
SBCCI; Southern Building Codes Congress International
SPFA; Spray Polyurethance Foam Alliance

UBC; Uniform Building Code
UL; Underwriter's Laboratories