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  • A

    Ammoniacal copper arsenate. One of several varieties of toxic pesticides used in pressure-treated wood; see also CCA (chromated copper arsenate).
    ACH stands for Air Changes per Hour. This is a metric of house air tightness. ACH is often expressed as ACH50, which is the air changes per hour when the house is depressurized to -50 pascals during a blower door test. The term ACHn or NACH refers to "natural" air changes per hour, meaning the rate of air leakage without blower door pressurization or depressurization. While many in the building science community detest this term and its use (because there is no such thing as "normal" or "natural" air leakage; that changes all the time with weather and other conditions), ACHn or NACH is used by many in the residential HVAC industry for their system sizing calculations.
    ACQ is a water-based wood preservative alternative to CCA for preserving wood that prevents decay from fungi and insects. There are four standardized ACQ formulations, Types A, B, C, and D. The different formulations allow achieving compatibility with different wood species and applications. All ACQ types contain 2 active ingredients which may vary within the following limits: copper oxide (62%-71%), which is the primary fungicide and insecticide, and a quaternary ammonium compound (29%-38%), which provides additional fungicide and insect resistance properties.
    Advanced Framing
    House-framing techniques in which lumber use is optimized, saving material and improving the energy performance of the building envelope.
    Advanced New Home Construction Program
    A U.S. Environmental Protection Agency (EPA) program to promote the construction of "better than Energy Star" homes.
    Annual Fuel Utilization Efficiency. Widely-used measure of the fuel efficiency of a heating system that accounts for start-up, cool-down, and other operating losses that occur during real-life operation. AFUE is always lower than combustion efficiency. Furnaces sold in the United States must have a minimum AFUE of 78%. High ratings indicate more efficient equipment.
    Air Barrier
    Building assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both.
    Air-source Heat Pump
    Heat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps.
    Angle Of Incidence
    In terms of solar energy, the angle that the sun's rays make with an imaginary line perpendicular to a surface. The angle of incidence determines the intensity of the energy that any surface “sees.”
    Annual Fuel Utilization Efficiency
    (AFUE) Widely-used measure of the fuel efficiency of a heating system that accounts for start-up, cool-down, and other operating losses that occur during real-life operation. AFUE is always lower than combustion efficiency. Furnaces sold in the United States must have a minimum AFUE of 78%. High ratings indicate more efficient equipment.
    American National Standards Institute. National nonprofit membership organization that coordinates development of national consensus standards. Accreditation by ANSI signifies that the procedures used meet the Institute’s essential requirements for openness, balance, consensus, and due process.
    APA-The Engineered Wood Association. Nonprofit trade association for manufacturers of engineered wood products, including glue-laminated timber (glulams), composite panels, wood I-joists, and laminated veneer lumber (lvls). APA and APA EWS (Engineered Wood Systems) trademarks identify products that meet the organization's manufacturing and performance guidelines. Formerly known as the American Plywood Association.
    Inert (chemically stable) gas, which, because of its low thermal conductivity, is often used as gas fill between the panes of energy-efficient windows.
    Mineral fiber once commonly used in many building materials, including insulation, fireproof siding, and resilient flooring. Inhalation of invisible asbestos fibers can lead to chest and abdominal cancers as well as scarring of the lungs. The use of asbestos in some products has been banned by the EPA and the U.S. Consumer Products Safety Commission; manufacturers also have adopted voluntary limitations on its use. When found in older buildings (most commonly in floor tiles, pipe and furnace insulation, or asbestos shingles), the product's friability is a major determinant in how it must be handled during renovations. More information:
    American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). International organization dedicated to the advancement of heating, ventilation, air conditioning, and refrigeration through research, standards writing, publishing, and continuing education. Membership is open to anyone in the HVAC&R field; the organization has about 50,000 members.
    ASHRAE 62.2
    A standard for residential mechanical ventilation systems established by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Among other requirements, the standard requires a home to have a mechanical ventilation system capable of ventilating at a rate of 1 cfm for every 100 square feet of occupiable space plus 7.5 cfm per occupant.
    The American Society of Interior Designers is a trade association representing the interior design professional community. ASID partnered with USGC to develop the REGREEN program, a green residential remodeling program (see
    American Society for Testing and Materials. Not-for-profit international standards organization that provides a forum for the development and publication of voluntary technical standards for materials, products, systems, and services. Originally the American Society for Testing and Materials.
  • B

    Indoor air quality problem in which potentially dangerous combustion gases escape into the house instead of going up the chimney.
    Practice of heating a building prior to occupancy (generally to about 100°F) to accelerate VOC emissions from furniture and materials. This practice is unproven and is not recommended.
    Balance Point
    Balance point is the outdoor temperature at which the amount of heating provided by an air source heat pump just equals the amount of heat lost from the house. Below this point, supplementary heat (typically inefficient electric resistance heat or “strip heat”) is required. Typical balance point temperatures are in the range of 27 - 35 degrees Fahrenheit.
    Balanced Ventilation
    Mechanical ventilation system in which separate, balanced fans exhaust stale indoor air and bring in fresh outdoor air in equal amounts; often includes heat recovery or heat and moisture recovery (see heat-recovery ventilator and energy-recovery ventilator).
    Batt Insulation
    Insulation, usually of fiberglass or mineral wool and often faced with paper, typically installed between studs in walls and between joists in ceiling cavities. Correct installation is crucial to performance.
    Literally “Building Biology,” a term coined in Germany to describe the use of holistic, healthy-building principles—particularly those focused on indoor air quality and electromagnetic fields—to safeguard the wellbeing of a building’s occupants.
    Glue used in manufactured wood products, such as medium-density fiberboard (MDF), particleboard, and engineered lumber. Some binders are made with formaldehyde. See urea-formaldehyde binder and methyl diisocyanate (MDI) binder.
    Biobased Material
    Material made from living matter, such as agricultural crops. Biobased materials are usually biodegradable.
    Chemicals toxic to microorganisms. Biocides, which include pesticides and antimicrobial agents, are used in paint, building materials, and floor coverings to kill bacteria, mold spores, insects, etc.
    Organic waste that can be converted to usable forms of energy such as heat or electricity, or crops grown specifically for that purpose.
    Practice of imitating nature in the design and/or production of buildings, systems, or products.
    Black Water
    Potentially contaminated wastewater from the toilet, kitchen sink, or other sources. Black water should not be reused without going through a complete treatment system.
    Blower-door Test
    Test used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas.
    Boron-containing chemical that provides fire resistance to materials such as cellulose insulation and provides decay and termite resistance to wood products. Borate is derived from the mineral borax and is benign, compared with most other wood treatments.
    British thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. One Btu is equivalent to 0.293 watt-hours or 1,055 joules.
    Build It Green
    Professional, nonprofit membership organization that promotes healthy, energy- and resource-efficient buildings in California. It was formed in 2005 in a merger of Bay Area Build It Green and The Green Resource Center of Berkeley. Headquartered in Berkeley, Build It Green offers professional training and other support services, maintains a regional green products database, and administers the Green Point Rated home certification program.
    Builders Challenge Program
    A U.S. Department of Energy (DOE) program to promote the construction of “better than Energy Star” homes. A home must have a maximum HERS rating of 70 to meet Builders Challenge requirements.
    Building Envelope
    Exterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials.
    Building Paper
    Typically referring to Grade D building paper, this product is an asphalt-impregnated kraft paper that looks a lot like a lightweight asphalt felt. The Grade D designation has come to mean that the building paper passes ASTM D779 (minimum 10-minute rating with the “boat test”) and different products are called out as “30-minute” or even “60-minute” based on D779 results. At times confused with roofing felt, roofing felts and building paper differ in two ways: felts are made of recycled-content paper, building papers of virgin paper; felts are made of a heavier stock paper; building papers a lighter stock. See also roofing felt.
    Built Green
    Environmental building program of the Master Builders Association of King and Snohomish counties in Washington state. Offers four rating systems that cover single family homes, remodels, multifamily dwellings, and communities; ratings are either self-certified or verified by a third party, depending on the level of certification.
    Built Green Colorado
    Joint effort of the Home Builders Association of Metro Denver, government, utilities, and product manufacturers to promote green building through training opportunities, technical support, and a Built Green designation for homes constructed using the program’s guidelines.
  • C

    Forces that lift water or pull it through porous materials, such as concrete. The tendency of a material to wick water due to the surface tension of the water molecules.
    Carbon Footprint
    Amount of carbon dioxide and other greenhouse gases that a person, community, industry, or other entity contributes to the atmosphere through energy use, transportation, and other means.
    Carbon Offset
    Carbon credits purchased to offset the purchaser’s carbon dioxide emissions.
    Catchment Area
    Surface, typically on a roof, where rainwater is caught and directed into a rainwater harvesting system.
    Cathedralized Attic
    An unvented attic with insulation installed between the rafters or above the roof sheathing. Moving the insulation from the attic floor to the roof plane turns the attic into conditioned or semi-conditioned space; this is especially beneficial in homes with attic ductwork. The term “cathedralized attic” usually refers to an attic that does not include finished space.
    Cavity Wall
    Wall assembly constructed of two wythes of masonry bonded with wall ties and separated by an air cavity, which is sometimes filled with insulation.
    CAZ Worst Case Depressurization Test
    A safety test in which the potential for backdrafting of combustion appliances is assessed by turning on all exhaust fans in a home and then visual assessing appliance combustion exhaust performance or using pressure testing to assess the extent of depressurization in the location of the combustion appliance.
    Cellulose Insulation
    Thermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection.
    Compact fluorescent lamp. Fluorescent lightbulb in which the tube is folded or twisted into a spiral to concentrate the light output. CFLs are typically three to four times as efficient as incandescent lightbulbs, and last eight to ten times as long. CFLs combine the efficiency of fluorescent light with the convenience of an Edison or screw-in base, and new types have been developed that better mimic the light quality of incandescents. Not all CFLs can be dimmed, and frequent on-off cycling can shorten their life. Concerns have been raised over the mercury content of CFLs, and though they have been deemed safe, proper recycling and disposal is encouraged.
    Meeting at the beginning of an integrative design process that sets the stage for cooperation and collaboration among all participants, including the design team, engineers, contractors, clients, and any others involved in the project. Early involvement of the entire project team is fundamental to the successful use of a systems approach to green building.
    Materials used on the roof and walls to enclose a house, providing protection against weather.
    Concrete masonry unit. Precast concrete block used to build walls. CMUs have hollow cores that can be filled with concrete onsite for additional reinforcement. The use of stronger, more lightweight types of concrete such as autoclaved aerated concrete (AAC) is becoming increasingly popular in CMU manufacture.
    Coefficient Of Performance
    Energy-efficiency measurement of heating, cooling, and refrigeration appliances. COP is the ratio of useful energy output (heating or cooling) to the amount of energy put in, e.g., a heat pump with a COP of 10 puts out 10 times more energy than it uses. A higher COP indicates a more efficient device . COP is equal to the energy efficiency ratio (EER) divided by 3.415.
    Development pattern in which multiple (typically 8 to 30) privately owned houses or housing units are clustered together with some commonly owned spaces, such as a common workshop, greenhouse, etc. Automobiles are typically kept to the perimeter of the community, creating a protected area within where children can play. Usually, residents are closely involved in all aspects of the development, from site selection to financing and design.
    Process of testing a home after a construction or renovation project to ensure that all of the home's systems are operating correctly and at maximum efficiency.
    Composite Lumber
    Lumber, typically decking, made from plastic (often high-density polyethylene) and wood fiber or other agricultural by-products. Composite lumber often contains recycled content. Also called composite decking.
    Conditioned Space
    Insulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort.
    Movement of heat through a material as kinetic energy is transferred from molecule to molecule; the handle of an iron skillet on the stove gets hot due to heat conduction. R-value is a measure of resistance to conductive heat flow.
    Cradle To Cradle
    Term used to describe the recycling of waste materials and manufactured products into new products rather than permanently disposing of them (see cradle to grave). The concept and its societal implications was the focus of the 2002 book Cradle to Cradle: Remaking the Way We Make Things by chemist Michael Braungart and architect William McDonough.
  • D

    Use of sunlight for daytime lighting needs. Daylighting strategies include solar orientation of windows as well as the use of skylights, clerestory windows, solar tubes, reflective surfaces, and interior glazing to allow light to move through a structure.
    Measure of how cold or warm a location is over a period of time relative to a base temperature, typically 65°F (although other base temperatures, such as 75°F, can be used for cooling). To calculate the number of heating degree-days (HDD) of a given day, average the maximum and minimum outdoor temperatures and subtract that from 65°F. The annual number of heating degree-days is a measure of the severity of the climate and is used to determine expected fuel use for heating. Cooling degree-days (CDD), which measure air conditioning requirements, are calculated by subtracting the average outdoor temperature from an indoor base temperature.
    Difference in temperature across a divider; often used to refer to the difference between indoor and outdoor temperatures.
    Situation that occurs within a house when the indoor air pressure is lower than that outdoors. Exhaust fans, including bath and kitchen fans, or a clothes dryer can cause depressurization, and it may in turn cause back drafting as well as increased levels of radon within the home.
    Design Temperature
    Reasonably expected minimum (or maximum) temperature for a particular area; used to size heating and cooling equipment. Often, design temperatures are further defined as the X% temperature, meaning that it is the temperature that is exceeded X% of the time (for example, the 1% design temperature is that temperature that is exceeded, on average, 1% of the time, or 87.6 hours of the year).
    Design-build Firm
    Company that handles house design and construction. Since both services are provided by the same firm, integrated design can often be more easily achieved.
    In a forced-air heating/cooling system, the diffuser is a register or grille attached to ducting through which heated or air conditioned air is delivered to the living space. In a tubular skylight or an electric light fixture, the diffuser is a cover plate through which scattered light is delivered.
    Direct-gain System
    Type of passive solar heating system in which south-facing windows provide heat gain during the daytime and high-mass thermal-storage materials absorb and store that heat. At night, the stored heat radiates back out, warming the space. This is the simplest type of passive solar heating system, but careful design is required to prevent overheating.
    Displacement Ventilation
    Ventilation that uses natural convection to move warm air up and out of a building; used in Scandinavia since the 1970s, it is being increasingly employed in the United States.
    Diurnal Flux
    Difference between day and night average temperatures.
    True divided light sash have small panes of glass separated by muntins. Because large pieces of glass used to be difficult (or expensive) to make, older houses have windows with two, four, or six small lights per sash. These multiple-light sash are also called "divided-light sash" or sometimes "divided-light windows."
    United States Department of Energy.
    Double-stud Wall
    Construction system in which two layers of studs are used to provide a thicker-than-normal wall system so that a lot of insulation can be installed; the two walls are often separated by several inches to reduce thermal bridging through the studs and to provide additional space for insulation.
    Drain-water Heat-recovery System
    DHR, also known as graywater heat-recovery system. System that extracts heat from hot-water waste lines to preheat cold water before it reaches the water heater or tap; especially useful when paired with on-demand or solar hot-water systems.
    Drainage Plane
    Path that water would take over the building envelope. Concealed drainage-plane materials, such as building paper or housewrap, are designed to shed water that penetrates the building’s cladding. Drainage planes are installed to overlap in shingle fashion (weatherlap) so that water flows downward and away from the building envelope.
    Dry Bulb Temperature
    Air temperature as measured by an ordinary thermometer.
    Dry Well
    Underground structure that captures, then slowly releases storm-water runoff so that it can be absorbed by the soil.
    Drywall Clips
    Metal or plastic stops that are attached to framing at inside corners. The clips replace framing, thus leaving more room for insulation. Because such a corner floats (acting as a stop, the clip allows the first sheet of drywall to be trapped by the second, perpendicularly installed sheet), cracking of the drywall joint is less common.
    Duct Blaster
    Calibrated air-flow measurement system developed to test the airtightness of forced-air duct systems. All outlets for the duct system, except for the one attached to the duct blaster, are sealed off and the system is either pressurized or depressurized; the work needed by the fan to maintain a given pressure difference provides a measure of duct leakage.
    Ductless Mini-split
    A type of small-capacity heat pump (as little as a ton or even less) with a closely-associated outside compressor and inside evaporating coil (often through-the-wall in design). These heat pumps often come with variable-speed compressors and blowers,giving them excellent modulation for thermal comfort. These features also contribute to COPs of around 4 for ductless min-split heat pumps. They are also well-suited for ultra-high performance, small-volume homes.
    Dutch Drain
    Open drain that carries storm-water runoff from the bottom of a house wall away from the house.
  • E

    Earth Tube
    Ventilation air intake tube, usually measuring 8 or more inches in diameter and buried 5 or more feet below grade. Earth tubes take advantage of relatively constant subterranean temperatures to pre-heat air in winter and pre-cool it in summer. In humid climates, some earth tubes develop significant amounts of condensation during the summer, potentially contributing to indoor air quality problems.
    Energy-efficiency rating or energy-efficiency ratio. As most commonly used, EER is the operating efficiency of a room air conditioner, measured in Btus of cooling output divided by the power consumption in watt-hours; the higher the EER, the greater the efficiency.
    Energy factor. Efficiency measure for rating the energy performance of dishwashers, clothes washers, water heaters, and certain other appliances. The higher the energy factor, the greater the efficiency. In some appliances EF reflects the percentage of energy going into the appliance that is turned into useful energy.
    Effective Leakage Area
    ELA. Calculation in square inches equal to the total area of all air leaks in a building envelope. Defined by Lawrence Berkeley National Laboratory, the ELA is the area of a nozzle-shaped hole that would leak the same amount of air as the building does when pressurized to 4 pascals. Estimating leakage in this way enables one to visualize the cumulative impact many tiny holes can have on the airtightness of a house.
    Effective leakage area. Calculation in square inches equal to the total area of all air leaks in a building envelope. Defined by Lawrence Berkeley National Laboratory, the ELA is the area of a nozzle-shaped hole that would leak the same amount of air as the building does when pressurized to 4 pascals. Estimating leakage in this way enables one to visualize the cumulative impact many tiny holes can have on the airtightness of a house.
    Embodied Energy
    Energy that goes into making a product; includes energy required for growth, extraction, and transportation of the raw material as well as manufacture, packaging, and transportation of the finished product. Embodied energy is often used to measure ecological cost.
    Amount of heat radiation emitted from a particular body or material. Emissivity is expressed in a fraction or ratio, with the lowest values indicating low emissivity and the highest indicating the high emissivity of flat black surfaces.
    Endocrine Disruptor
    Chemical that mimics natural hormones, such as estrogen, and may interfere with hormone-affected processes, including reproduction and development. Includes such commonly used chemicals as phthalate plasticizers used in PVC plastic, and bisphenol-A, used in epoxies and polycarbonate plastic.
    Energy Factor
    (EF). Efficiency measure for rating the energy performance of dishwashers, clothes washers, water heaters, and certain other appliances. The higher the energy factor, the greater the efficiency. In some appliances EF reflects the percentage of energy going into the appliance that is turned into useful energy.
    Energy Star
    Labeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners.
    Energy Star Homes
    A U.S. Environmental Protection Agency (EPA) program to promote the construction of new homes that are at least 15% more energy-efficient than homes that minimally comply with the 2004 International Residential Code. Energy Star Home requirements vary by climate.
    Energy Star Indoor Air Package
    A U.S. Environmental Protection Agency (EPA) program to promote the construction of new homes that are less likely to have indoor air problems than conventional homes. Homes complying with the EPA Indoor Air Package must meet Energy Star Homes requirements as well as additional specifications addressing indoor air quality. Among the program’s requirements are details designed to limit water entry into basements, requirements for radon mitigation components in geographical areas with potential radon problems, a requirement for sill pan flashing at window rough openings, mandatory roof gutters except in dry climates, a mandatory layer of rubberized asphalt under roof valleys, a duct sealing specification, a prohibition against locating furnaces in garages, and a requirement for a mechanical ventilation system that complies with ASHRAE 62.2. The Energy Star Indoor Air Package requirements are similar but not identical to the American Lung Association’s Heath House requirements.
    Energy Star Window Standard
    A standard for window performance established by the U.S. Department of Energy (DOE). Energy Star window criteria are climate-zone dependent; the DOE divides the country into four climate zones. In the northern zone, the U-factor of an Energy Star window must be no higher than 0.35. Energy Star windows sold in the southern zone must have a maximum U-factor of 0.75 and a maximum solar heat gain coefficient (SHGC) of 0.40. The criteria for the two central zones fall within the ranges established by the coldest and warmest zones. (The maximum U-factor for GreenSpec-listed windows is 0.30; GreenSpec does not include minimum or maximum SHGC criteria.) Many critics have noted that the Energy Star program has set a low bar for window performance. In most jurisdictions, Energy Star windows are no better than windows that minimally comply with building code requirements.
    Energy Truss
    Also called high-heeled truss, raised-heel truss, energy heel, Arkansas truss. Framing method in which roof trusses are raised at the point where the rafters connect to the top plate of the exterior wall to allow room for effective insulation.
    Energy-efficiency Rating
    (EER). As most commonly used, EER is the operating efficiency of a room air conditioner, measured in Btus of cooling output divided by the power consumption in watt-hours; the higher the EER, the greater the efficiency.
    Energy-efficient Mortgage
    (EEM). Special type of mortgage in which the lending institution raises the allowable loan amount for the applicant's earnings level because energy-saving features in the house will reduce its monthly operating costs, leaving more money available to pay the mortgage.
    Energy-recovery Ventilator
    (ERV). The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV.
    Engineered Header
    Framing member made of engineered lumber and used to carry a wall or roof load above a window or door.
    Engineered Lumber
    Lumber made by gluing together veneers or strands of wood to create very strong framing members; stronger and less prone to warping than standard framing lumber and can be made from smaller-diameter trees, saving old-growth forests.
    Environments For Living
    (EFL). A green building program that focuses on building science to improve home energy efficiency and comfort. EFL is administered by Masco Contractor Services.
    Expanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.
    Energy-recovery ventilator. The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV.
    European Eco-label
    (EU Eco-Label). Label identifying products and services that have been certified as environmentally friendly by the European Eco-labeling Board. The label is available to any product or service except food, drink, pharmaceuticals, and medical devices.
    Evacuated-tube Solar Collector
    Solar collector consisting of a series of glass vacuum tubes in which an inner tube containing fluid (or in some types, a metal plate) absorbs heat energy and transfers it for practical use, usually water heating.
    Airflow outward through a wall or building envelope; the opposite of infiltration.
    Exhaust-only Ventilation
    Mechanical ventilation system in which one or more fans are used to exhaust air from a house and make-up air is supplied passively. Exhaust-only ventilation creates slight depressurization of the home; its impact on vented gas appliances should be considered.
  • F

    Technically, any transparent or translucent material plus any sash, frame, mullion, or divider attached to it, including windows, skylights, glass doors, and curtain walls.
    Ferro Cement
    Mix of portland cement, sand, and water that is sprayed on a steel mesh, creating a thin, strong material; often used for cisterns.
    First Cost
    Initial cost of buying or building something; does not include operating costs.
    Flat Plate Collector
    Fat, box-shaped solar collector that uses a dark-colored metal plate to absorb radiant heat and transfer it to a circulating liquid or gas that can be used immediately or stored for later use. Typically used for domestic hot water or space heating.
    Carbon-fluorine compounds that often contain other elements such as hydrogen, chlorine, or bromine. Fluorocarbons are used as refrigerants and propellants in aerosol products, among other uses. Common fluorocarbons include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs). In 1978 the United States began phasing out the use of CFCs because of their ozone-depleting effect.
    Polymer (compound made up of many identical molecules linked by chemical bonds) containing the element fluorine. The most recognized fluoropolymer is DuPont’s Teflon, or polytetrafluoroethylene (PTFE). A key constituent in making fluoropolymers, perfluorooctanoic acid (PFOA), has come under fire as a "likely carcinogen."
    Specific time period during which a new building’s materials are allowed to cure and release toxic substances prior to occupation.
    Fly Ash
    Fine particulates consisting primarily of silica, alumina, and iron that are collected from flue gases during coal combustion. Flyash is employed as a substitute for some of the portland cement used in the making of concrete, producing a denser, stronger, and slower-setting material while eliminating a portion of the energy-intensive cement required. More info
    To fog a room or building is to use a fog machine during a blower door test, revealing locations of air leaks where the fog escapes. The fogging material is usually a glycol-based solution, completely non-toxic.
    Forest Stewardship Council
    (FSC) Nonprofit organization that promotes forestry practices that are sustainable from environmental and social standpoints; FSC certification on a wood product is an indicator that the wood came from a well-managed forest.
    Chemical found in many building products; most binders used for manufactured wood products are formaldehyde compounds. Reclassified by the United Nations International Agency for Research on Cancer (IARC) in 2004 as a “known human carcinogen."
    Easily broken down. A friable insulation material may lose its effectiveness; some friable materials release hazardous dust into the home.
    Nonprofit organization that promotes forestry practices that are sustainable from environmental and social standpoints; FSC certification on a wood product is an indicator that the wood came from a well-managed forest.
    Fuel Cell
    Electrochemical device in which electricity is generated by chemically reacting hydrogen with oxygen; electricity, water vapor, and heat are the only products. Unlike a battery, which stores a limited fuel supply used to create electricity, a fuel cell draws on an ongoing supply of fuel to produce electricity continuously.
    Substance that kills fungi, including mold and mildew, and yeasts.
  • G

    This is a gable roof with two pitches, the bottom pitch being steeper than the top. The term gambrel is also used to describe the hing leg of a horse, with a angle at the joint that looks like a gambrel roof, or much more likely, the other way around.
    Geothermal Energy
    Hot water or steam extracted from reservoirs beneath the Earth's surface; can be used for heat pumps, water heating, or electricity generation. The term may also mean the use of near-constant underground temperatures by ground-source heat pumps to provide heating and cooling.
    When referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill.
    Gallons per flush. Measurement of water use in toilets. Since 1992, toilets sold in the United States have been restricted to 1.6 gpf or less. The standard for high-efficiency toilets (HETs) is 1.28 gpf.
    Gallons per minute. Measure of liquid (usually water) flow.
    Wastewater from a building that does not include flush-water from toilets and (as most commonly defined) water from kitchen sinks or dishwashers. In some places, graywater can be collected and used for subsurface irrigation.
    Green Electricity
    Electricity generated from renewable energy sources, such as photovoltaics (solar power), wind power, biomass, and small-scale hydropower. (Large, conventional hydropower sources usually are not included in definitions of green electricity.)
    Green Mortgage
    Green mortgage Type of mortgage in which the lending institution raises the allowable loan amount for an applicant's earnings level because the applicant's green home has lower monthly operating costs and may even reduce the applicant's transportation costs. See energy efficient mortgage.
    Green Roof
    Roof system in which living plants are maintained in a growing medium using a membrane and drainage system. Green roofs can reduce storm-water runoff, moderate temperatures in and around the building (by providing insulation and reducing heat island effect), as well as provide a habitat for wildlife and recreational space for humans. When properly constructed, green roofs can increase roof durability because the roof assembly’s air and water barriers are buffered from temperature fluctuations and UV exposure.
    Green Seal
    Independent, nonprofit organization that certifies a variety of products as environmentally responsible based on established criteria. Certified products include coffee filters, air chillers, paints and coatings, papers and newsprint, various cleaning products and services, windows and doors, and lodging properties.
    Third-party certification program that identifies building products and materials which produce relatively low levels of emissions. GreenGuard is administered by the nonprofit GreenGuard Environmental Institute (GEI). Other GEI programs include the Children & Schools standard, which addresses emission standards for educational facilities, and the GreenGuard for Building Construction Program, a mold risk-reduction program that certifies the design, construction, and ongoing operations of new multifamily and commercial properties.
    Dissemination of misleading or false information designed to make an organization or product appear more environmentally friendly than it actually is.
    Ground-source Heat Pump
    Home heating and cooling system that relies on the mass of the earth as the heat source and heat sink. Temperatures underground are relatively constant. Using a ground-source heat pump, heat from fluid circulated through an underground loop is transferred to and/or from the home through a heat exchanger. The energy performance of ground-source heat pumps is usually better than that of air-source heat pumps; ground-source heat pumps also perform better over a wider range of above-ground temperatures.
    Building renovation in which all interior walls and ceilings are removed, leaving framing and exterior sheathing or structural brick or block.
    Gypsum Board
    Often referred to as drywall or Sheetrock. Flat sheet of the mineral gypsum, usually faced with paper, that is used as a building material for interior (and sometimes exterior) walls and ceilings.
  • H

    Class of man-made chemicals, including chlorofluorocarbons (CFCs), hydrocholorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs), whose heat-trapping properties are among the most damaging of the greenhouse gases. This, coupled with their tendency to remain in the atmosphere for hundreds of years, has resulted in limits on their use. Halocarbons are most commonly used in refrigeration, air conditioning, and electrical systems, and as blowing agents in some foam insulation products.
    Heat Exchanger
    Device that transfers heat from one material or medium to another. An air-to-air heat exchanger, or heat-recovery ventilator, transfers heat from one airstream to another. A copper-pipe heat exchanger in a solar water-heater tank transfers heat from the heat-transfer fluid circulating through a solar collector to the potable water in the storage tank.
    Heat Gain
    Increase in the amount of heat in a space, including heat transferred from outside (in the form of solar radiation) and heat generated within by people, lights, mechanical systems, and other sources. See heat loss.
    Heat Pump
    Heating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump.
    Heat Sink
    Where heat is dumped by an air conditioner or by a heat pump used in cooling mode; usually the outdoor air or ground. See air-source heat pump and ground-source heat pump.
    Heat-pump Water Heater
    An appliance that uses an air-source heat pump to heat domestic hot water. Most heat-pump water heaters include an insulated tank equipped with an electric resistance element to provide backup heat whenever hot water demand exceeds the capacity of the heat pump. Since heat-pump water heaters extract heat from the air, they lower the temperature and humidity of the room in which they are installed.
    Heat-recovery Ventilator
    (HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air.
    Heating Degree Day
    The difference between the 24-hour average (daily) temperature and the base temperature for one year for each day that the average is below the base temperature. For heating degree days, the base is usually 65 degrees Fahrenheit. For example, if the average temperature for December 1, 2001 was 30 degrees Fahrenheit, then the number of heating degrees for that day was 35.
    Heating Load
    Rate at which heat must be added to a space to maintain a desired temperature. See cooling load.
    Heavy Metals
    Metallic elements with high atomic weights, including mercury, lead, cadmium, arsenic, and chromium. Released as industrial pollutants, some heavy metals are toxic and may accumulate to hazardous levels in the food chain. Different from Heavy Metal, which is a type of music frequently heard on job sites.
    Index or scoring system for energy efficiency established by the Residential Energy Services Network (RESNET) that compares a given home to a Home Energy Rating System (HERS) Reference Home based on the 2006 International Energy Conservation Code. A home matching the reference home has a HERS Index of 100. The lower a home’s HERS Index, the more energy efficient it is. A typical existing home has a HERS Index of 130; a net zero energy home has a HERS Index of 0. Older versions of the HERS index were based on a scale that was largely just the opposite in structure--a HERS rating of 100 represented a net zero energy home, while the reference home had a score of 80. There are issues that complicate converting old to new or new to old scores, but the basic formula is: New HERS index = (100 - Old HERS score) * 5.
    High-efficiency Toilet
    (HET). Toilet that provides at least 20% water savings over the federal standard of 1.6 gpf and still meets the most rigorous standards for flush performance. HETs include pressure-assist toilets that use as little as 1.0 gpf, gravity-flush toilets that consume 1.28 gpf, and dual-flush toilets that offer two different flush volumes.
    Home Energy Performance Audit
    Energy audit that also includes inspections and tests to assess moisture flow, combustion safety, thermal comfort, indoor air quality, and durability.
    Home Performance With Energy Star
    A residential weatherization program jointly administered by the U.S. Department of Energy and the U.S. Environmental Protection Agency. The Home Performance With Energy Star program connects homeowners interested in improving the energy performance of their homes with contractors trained to assess home performance and perform energy retrofit work.
    Home-run Plumbing System
    Water-distribution piping system in which individual plumbing lines extend from a central manifold to each plumbing fixture or water-using appliance; piping is typically cross-linked polyethylene (PEX). Depending on patterns of use, hot water may be delivered more quickly in such a system because the diameter of the tubing can be matched to the flow of the fixture or appliance.
    (Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building.
    (HCFC). Compound commonly used as a refrigerant in compression-cycle mechanical equipment (refrigerators, air conditioners, and heat pumps) or as a blowing agent to produce foam insulation. HCFCs are damaging to the Earth’s protective ozone layer, but less so than chlorofluorocarbons (CFCs).
    A device that measures relative humidity of air. Mechanical hygrometers that rely on a coil of thin metal are not terribly accurate; electronic hygrometers available at most electronic or hardware stores are usually accurate to about plus or minus 2 - 3%.
    A term used to characterize the temperature (thermal) and moisture (hygro) conditions particularly with respect to climate, both indoors and out.
  • I

    Indoor air quality. Healthfulness of an interior environment; IAQ is affected by such factors as moisture and mold, emissions of volatile organic compounds from paints and finishes, formaldehyde emissions from cabinets, and ventilation effectiveness.
    This is the International Code Council Evaluation Service. ICC-ES is a non-profit public benefit corporation that evaluates building products, issuing final reports on code compliance of building products and materials. These reports on then made available at no charge to the building community at large.
    Ice Dam
    A ridge of ice that forms along the lower edge of a roof, possibly leading to roof leaks. Ice dams are usually caused by heat leaking from the attic, which melts snow on the upper parts of the roof; the water then refreezes along the colder eaves working it's way back up the roof and under shingles.
    Insulated concrete form. Hollow insulated forms, usually made from expanded polystyrene (EPS), used for building walls (foundation and above-ground); after stacking and stabilizing the forms, the aligned cores are filled with concrete, which provides the wall structure.
    Integral collector storage solar water heater.
    Open-cell, low-density spray foam insulation that can be used in wall, floor, and roof assemblies. It has an R-value of about 3.6 per inch and a vapor permeability of about 10 perms at 5 inches thick.
    International Energy Conservation Code.
    Indirect Water Heater
    Water heater that draws heat from a boiler used for space heating; a separate zone from the boiler heats potable water in a separate, insulated tank via a water-to-water heat exchanger. See tankless coil.
    Inert Ingredient
    Product component that is not directly responsible for the primary function of that product. For example, an inert ingredient in a pesticide does not kill the pests, but may be added to simplify application, improve shelf life, or enhance effectiveness. Inert ingredients may or may not be toxic.
    Infill Site
    Building site sandwiched between existing buildings in a developed area. The use of infill sites reduces pressure on greenfield sites and often provides residents with better access to public transportation. For the purposes of LEED for Homes credits, an infill site is defined as having at least 75% of its perimeter bordering land that has been previously developed.
    Infrared Thermometer
    A digital thermometer capable of measuring the temperature of a surface from a distance ranging from a few inches to a few feet. Most hand-held infrared thermometers include a laser to help aim the device; the laser plays no role in temperature measurement. Used as an inexpensive substitute for a thermal imaging camera, an infrared thermometer can detect hot or cold spots on walls, ceilings, and duct systems.
    Amalgamation of the words “incoming solar radiation” that means the total amount of solar energy that strikes a given surface in a given time. It is commonly expressed in kilowatt-hours per square meter per day.
    Integrated Design
    Building design in which different components of design, such as the building envelope, window placement and glazings, and mechanical systems are considered together. High-performance buildings and renovations can be created cost-effectively using integrated design, since higher costs one place can often be paid for through savings elsewhere, for example by improving the performance of the building envelope, the heating and cooling systems can be downsized, or even eliminated.
    Device for converting direct-current (DC) electricity into the alternating-current (AC) form required for most home uses; necessary if home-generated electricity is to be fed into the electric grid through net-metering arrangements.
    International Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code.
  • J

    Jump Duct
    Flexible duct that connects a room to a common space to balance pressure and to provide a pathway for return air in forced-air heating and cooling systems. Jump duct grilles are typically located in the ceiling.
  • K

    1,000 Btus
    A colorless, odorless inert gas, often used with argon in fluorescent lighting and sometimes used as gas fill in high-performance glazing.
    Kyoto Protocol
    An international agreement reached in Kyoto, Japan, in December 1997 in which industrialized nations agreed to make substantial reductions in the emission of greenhouse gases by 2012. Gases included under the protocol include carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.
  • L

    Latent Load
    Cooling load that results when moisture in the air changes from a vapor to a liquid (condensation). Latent load puts additional demand on cooling systems in hot-humid climates.
    Life-cycle assessment. Examination of environmental and health impacts of a product or material over its life cycle; provides a mechanism for comparing different products and materials for green building.
    Light-emitting diode. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed.
    Leadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify.
    Living Machine
    Ecological wastewater treatment system that relies on biological systems (microorganisms, plants, and animals) to purify wastewater; usually used in municipal-scale treatment systems.
    Low-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor.
    Low-e Coating
    Very thin metallic coating on glass or plastic window glazing that reduces heat loss through the window; the coating emits less radiant energy (heat radiation), which makes it, in effect, reflective to that heat; boosts a window’s R-value and reduces its U-factor.
    Low-flow Showerhead
    Showerhead that restricts water flow to less than the 2.5 gpm limit (at 80 psi) mandated by the U.S. EPA.
    Laminated strand lumber . Engineered wood product developed in the 1980s in which wood strands are glued together and pressed into forms using steam injection. The strength and stability of LSL falls between that of conventional lumber and laminated veneer lumber (LVL).
    Laminated veneer lumber. Engineered wood product in which wood veneers are glued together in thick sections for use as beams or other structural members. LVL is stronger, straighter, and less prone to warping or shrinkage than conventional lumber and does not require the destruction of mature trees.
  • M

    Mean Radiant Temperature
    Mean radiant temperature (MRT) is roughly the average temperature of all the objects or surfaces that a person "sees" inside a building, with the surface temperatures being weighted by their area. A surface or object's contribution to MRT is also based on its temperature in comparison to the person (temperature difference or differential) and the viewing angle between the person and the surface.
    A strip of wood or metal separating and holding panes of glass in a window sash. Each pane of glass (or each "insulated glazing unit") separated by a muntin is called a light.
  • N

    National Association of Home Builders, which awards a Model Green Home Certification.
    NAHB Green Building Program
    The NAHB Green Building Program includes: the NAHB Model Green Home Building Guidelines, the National Green Building Conference, the NAHB Green website, the Green Building Program Hotline, the National Green Building Program Awards, the Certified Green Professional Designation, and the green building training and education that support the designation and guidelines.
    NAHB Model Green Home Building Guidelines
    These guidelines were finalized in 2004/2005 and are "...a tool kit for home builder associations to creae new programs and to help those programs expand and flourish." Builders can sign up on the NAHB Green website to use their web-based scoring tool to assess their project(s) according to the Guidelines. As soon as the ANSI National Green Building Standard is available, builders will be able to score their projects according to the Guidelines and/or the standard.
    National Green Building Standard
    National Green Building Standard Based on the NAHB Model Green Home Building Guidelines and passed through ANSI. This standard can be applied to both new homes, remodeling projects, and additions.
    National Green Building Standard (NGBS)-Remodel
    The NGBS is designed to work with remodeling projects in the following ways: 1. If the remodeling project involves 75% or more of the conditioned floor area, than this is considered a gut rehab and follows the program structure for new homes. 2. If the remodeling project is less than 75% of the home's conditioned floor area and the home was built prior to 1980, then the remodeling project can follow the "Remodel Path," meaning measured % improvements in energy and water efficiency and compliance with a list of 28 mandatory practices. 3. if the remodeling project is less than 75% of the home's conditioned floor area and the home was built during or after 1980, then the project must follow the "Green Building Path," which uses the new home point system with notes for line items that differ for remodeling projects.
    North East Sustainable Energy Association. A regional membership organization promoting sustainable energy solutions. NESEA is committed to advancing three core elements: sustainable solutions, proven results and cutting-edge development in the field. States included in this region stretch from Maine to Maryland.
    Net Metering
    Arrangement through which a homeowner who produces electricity using photovoltaics or wind power can sell excess electricity back to the utility company, running the electric meter backwards.
    Net Zero
    Producing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. Calculating net-zero energy can be difficult, particularly in grid-tied renewable energy systems, because of transmission losses in power lines and other considerations.
    Net-zero Energy
    Producing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines.
  • O

    On-demand Hot Water
    System to quickly deliver hot water to a bathroom or kitchen when needed, without wasting the water that has been sitting in the hot-water pipes, which circulates back to the water heater.
    Operative Temperature
    In determining thermal comfort, operative temperature is roughly the average of the air and mean radiant temperature (MRT) a person is experiencing.
    Ozone Depletion Potential
    Amount of damage to the ozone layer a given chemical can cause compared to trichlorofluoromethane (CFC-11), which is given a value of 1.0 on this relative scale.
  • P

    Passive Heating
    Space heating that does not require electricity or fuel consumption. The most common type of passive heating system is passive solar heating — that is, heating which depends on solar gain through windows, thermal mass, and insulation. Unlike an active solar heating system, a passive system has no pumps or blowers.
    Passivhaus Standard
    A residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates.
    Peak Watt
    Unit of rated power output, for example from a photovoltaic (PV) module in full sunlight, as distinct from its output at any given moment, which may be lower.
    PERSIST Construction
    A method of construction including rainscreen cladding and foam insulation installed on the exterior of the building’s frame. Developed by the National Research Council of Canada in the 1960s, PERSIST is an acronym for Pressure-Equalized Rain-Screen Insulated Structure Technique. (Some PERSIST builders prefer a different acronym: REFORM, for Rigid Exterior Foam Over Rubberized Membrane). Most PERSIST buildings have no insulation in the stud bays or rafter bays. Instead, 4 to 8 inches of rigid foam insulation is installed on the exterior of the wall and roof sheathing. The PERSIST system requires the installation of a rubberized asphalt membrane between the exterior foam and the wall and roof sheathing; this membrane acts as a water-resistant barrier, air barrier, and vapor barrier.
    Cross-linked polyethylene. Specialized type of polyethylene plastic that is strengthened by chemical bonds formed in addition to the usual bonds in the polymerization process. PEX is used primarily as tubing for hot- and cold-water distribution and radiant-floor heating.
    (PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow.
    Chemical often added to polyvinyl chloride (PVC) and certain other plastics to make them more flexible; some phthalates are considered endocrine disruptors.
    Picocuries Per Liter
    Abbreviated pCi/L, this term refers to the relative radioactivity contributed by radon gas to one liter (1,000 cc's) of air. A picocurie is one-millionth of a curie and represents about 2 radioactive particle disintegrations per minute. EPA has established an action limit (the level at which some form of radon mitigation should take place) of 4 pCi/L.
    Polyisocyanurate foam is usually sold with aluminum foil facings. With an R-value of 6 to 6.5 per inch, it is the best insulator and most expensive of the three types of rigid foam. Foil-faced polyisocyanurate is almost impermeable to water vapor; a 1-in.-thick foil-faced board has a permeance of 0.05 perm. While polyisocyanurate was formerly manufactured using HCFCs as blowing agents, U.S. manufacturers have now switched to pentane. Pentane does not damage the earth’s ozone layer, although it may contribute to smog.
    Porous Paving
    A paving material that allows rainfall to percolate through and infiltrate the ground, rather than contributing to stormwater runoff; can be asphalt, concrete, or porous grid paver.
    Post-consumer Recycled Material
    Material recovered from a waste product that has been in use by a consumer before being discarded.
    Post-industrial Recycled Material
    Material recovered from the waste stream of an industrial process (pre-consumer) that has not been placed in use.
    Pressure-assist Toilet
    Toilet that uses air pressure, generated as the toilet tank refills, to produce a more forceful flush; some of the highest-performance, high-efficiency toilets (HETs) rely on pressure-assist technology.
    Photovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow.
  • R

    Measure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor.
    Colorless, odorless, short-lived radioactive gas that can seep into homes and result in lung cancer risk. Radon and its decay products emit cancer-causing alpha, beta, and gamma particles.
    Construction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch.
    Rankine-cycle Compressor
    Technology used in a standard air conditioner and refrigerator to achieve cooling; a refrigerant is alternately compressed and allowed to expand, cooling air in the process.
    Roofing Felt
    Originally made with cotton rag content, this asphalt saturated product is now made of paper. At times confused with building paper, roofing felts and building paper differ in two ways: felts are made of recycled-content paper, building papers of virgin paper; felts are made of a heavier stock paper; building papers a lighter stock. ASTM qualifies roofing felts with the following ratings: ASTM D4869 (Type 1 with a minimum weight of 8 pounds per 100 square feet) and ASTM D226 (Type 2 with a minimum weight of 11.5 pounds per 100 square feet). “#15” felt used to weigh 15 pounds per 100 square feet, but not anymore; non-ASTM felts can weigh as little as 7 pounds per 100 square feet. Although felts do not bend as easily as building paper, felts are commonly used or even preferred on walls because of their ability to hold more water without deterioration. See also building paper.
  • S

    Sealed Combustion
    Combustion system for space heating or water heating in which outside combustion air is fed directly into the combustion chamber and flue gasses are exhausted directly outside.
    Seasonal Energy Efficiency Ratio
    (SEER) The efficiency of central air conditioners is rated by the Seasonal Energy Efficiency Ratio. The higher the SEER rating of a unit, the more energy efficient it is. The SEER rating is Btu of cooling output during a typical hot season divided by the total electric energy in watt-hours to run the unit. For residential air conditioners, the federal minimum is 13 SEER. For an Energy Star unit, 14 SEER. Manufacturers sell 18-20 SEER units, but they are expensive.
    Section R104.11
    "The provisions of this code are not intended to prevent the installation of any material or to prohibit any design or method of construction not specifically prescribed by this code, provided that any such alternative has been approved. An alternative material, design or method of construction shall be approved where the building official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, at least the equivalent of that prescribed in this code. Compliance with the specific performance-based provisions of the International Codes in lieu of specific requirements of this code shall also be permitted as an alternate." --2006 International Residential Code
    Section R502.11.1
    Wood trusses shall be designed in accordance with approved engineering practice. The design and manufacture of metal plate connected wood trusses shall comply with ANSI/TPI 1. International Residential Code
    Section R703.8
    Approved corrosion-resistant flashing shall be applied shingle-fashion in such a manner to prevent entry of water into the wall cavity or penetration of water to the building structural framing components. International Residential Code
    Section R703.9
    All Exterior Insulation Finish Systems (EIFS) shall be installed in accordance with the manufacturer’s installation instructions and the requirements of this section. Decorative trim shall not be face nailed through the EIFS. The EIFS shall terminate not less than 6 inches (152 mm) above the finished ground level. International Residential Code
    Seasonal Energy Efficiency Ratio (SEER) is the total cooling output (in BTU) of an air conditioner or heat pump during its normal annual usage period divided by its total energy input (in Watt-hours) during the same period. The units of SEER are Btu/W·h. SEER measures how efficiently a residential central cooling system operates over an entire cooling season. The relationship between SEER and EER depends on location, because equipment performance varies with climate factors like air temperature and humidity.
    Sensible Load
    This is the heat content of just the air; it does not include the heat content required to remove (condense) moisture from air. Sensible heat is measured by dry bulb temperature. Latent heat is measured by wet bulb temperature.
    Material, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen.
    Sheet Goods
    Material, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen.
    Solar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.
    Solar Heat Gain Coefficient
    (SHGC) The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.
    Stack Effect
    Also referred to as the chimney effect, this is one of three primary forces that drives air leakage in buildings. When warm air is in a column (such as a building), its buoyancy pulls colder air in low in buildings as the buoyant air exerts pressure to escape out the top. The pressure of stack effect is proportional to the height of the column of air and the temperature difference between the air in the column and ambient air. Stack effect is much stronger in cold climates during the heating season than in hot climates during the cooling season.
    Standard 55
    This is the ASHRAE standard for thermal comfort, entitled Thermal Environmental Conditions for Human Occupancy. Based in large part on the original work done by P. Ole Fanger, it takes into account all of the factors that affect human thermal comfort: air temperature, mean radiant temperature, relative humidity, air speed, local discomfort, and temperature variations over time (with the first two parameters being the most influential and when combined called operative temperature).
    Structural Insulated Panel
    (SIP) Building panel usually made of oriented strand board (OSB) skins surrounding a core of expanded polystyrene (EPS) foam insulation. SIPs can be erected very quickly with a crane to create an energy-efficient, sturdy home.
  • T

    Unit of heat equal to 100,000 British thermal units (Btus); commonly used for natural gas.
    Thermal Bridging
    Heat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel.
    Thermal Imaging Camera
    A camera that provides an image showing radiation in the infrared range of the electromagnetic spectrum. Since the amount of infrared radiation emitted from a surface varies with temperature, a thermal imaging camera is a useful tool for detecting hot or cold areas on walls, ceilings, roofs, and duct systems. When used to scan a building envelope, a thermal imaging camera can detect missing insulation or locations with high levels of infiltration. Thermal imaging cameras can provide useful information when the difference in temperature (delta T) between the indoors and the outdoors is as low as 18F°; however, the higher the delta T, the easier it is to see building defects.
    Thermal Mass
    Heavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night.
    Top Plate
    In wood-frame construction, the framing member that forms the top of a wall. In advanced framing, a single top plate is often used in place of the more typical double top plate.
    Tubular Skylight
    Round skylight that transmits sunlight down through a tube with internally reflective walls, even through an attic space; it delivers daylighting through a ceiling light diffuser. Most tubular skylights are 12 to 16 inches in diameter and deliver daytime lighting comparable to several 100-watt incandescent light bulbs.
  • U

    Measure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value.
    Universal Design
    Design that makes a building accessible to as many individuals as possible, including older people and those with physical handicaps.
    United States Green Building Council (USGBC). Organization devoted to promoting and certifying green buildings. USGBC created the LEED rating systems.
  • V

    Vapor Diffusion
    Movement of water vapor through a material; water vapor can diffuse through even solid materials if the permeability is high enough.
    Vapor Profile
    A vapor profile is an assessment of the relative vapor permeabilities of each individual component in a building assembly and a determination of the assembly's overall drying potential and drying direction based on vapor permeabilities of all of the components. The vapor profile addresses not only how the building's enclosure assembly protects itself from getting wet, but also how it dries when it gets wet. For a detailed treatment of this subject, see Building Science Corporation's article Understanding Vapor Barriers.
    Common term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate).
    Volatile organic compound. An organic compound that evaporates readily into the atmosphere; as defined by the U.S. Environmental Protection Agency, VOCs are organic compounds that volatize and then become involved in photochemical smog production.
    Volatile organic compound. An organic compound that evaporates readily into the atmosphere; as defined by the U.S. Environmental Protection Agency, VOCs are organic compounds that volatize and then become involved in photochemical smog production.
  • W

    Waste Management Plan
    Plan that addresses the collection and disposal of waste generated during construction or renovation, usually including the collection and storage of recyclable materials.
    Water-resistive Barrier
    Sometimes also called the weather-resistive barrier, this layer of any wall assembly is the material interior to the wall cladding that forms a secondary drainage plane for liquid water that makes it past the cladding. This layer can be building paper, housewrap, or even a fluid-applied material.
    Program developed and administered by the U.S. Environmental Protection Agency to promote and label water-efficient plumbing fixtures.
  • X

    Type of landscaping that requires little if any irrigation; suited to dry and drought-prone climates; generally relies on regionally adapted native plants.
    Extruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.

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