Glossary of Terms
Following is a list of some of the most common and important green materials and methods that might be helpful to you. It is not meant to be comprehensive, but hopefully it will guide you toward more sustainable choices. For a more exhaustive glossary of green building terms, visit www.whygreenbuildings.com/glossary.php.
Advanced framing: A technique for framing houses that saves on materials (including lumber) and improves energy performance.
Biomass: A term that refers to a renewable energy source derived from biological materials, namely wood and organic waste that is converted into usable forms of energy, such as heat or electricity.
Black water: A term that refers to water exclusively from toilets, kitchen sinks that contains contaminated wastewater, which must pass through a complete treatment system in order to be reused. It is distinct from greywater and in autonomous buildings must remain separate.
Blower-door test: A test used to measure the amount of air leakage in the home. A fan is mounted in an exterior doorway that blows air to pressurize or de-pressurize the house. The force needed to maintain a constant pressure difference is a measure of the homes air-tightness. After determining air leakage, weak areas can be sealed by weatherization contractors.
British Thermal Unit (BTU): The amount of heat required to raise one pound of water (about a pint) one degree Farenheit in temperature-about the heat content of one wooden kitchen match. One BTU is equivalent to 0.293 watt-hours or 1,055 joules.
Building envelope: The exterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation. This includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials.
Carbon footprint: The 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.
Catchment area: The surface, typically on a roof, where rainwater is caught and directed into a rainwater harvesting system.
Cellulose insulation: A type of thermal insulation made from recycled newspaper or other wastepaper, often treated with borates for fire and insect protection.
Compact Fluorescent Lamp (CFL): A 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. 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.
Cladding: Materials used on the roof and walls to enclose a house, providing protection against weather and an aesthetic element.
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. It is also called composite decking.
Daylighting: The 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.
Degree-day: The 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. Synonyms include heating degree-days (HDD) and cooling degree-days (CDD).
Double-stud wall: A 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.
Embodied energy: A term that refers to the amount of energy that goes into making a product. This includes energy required for growth, extraction, and transportation of the raw material as well as manufacturing, packaging, and transportation of the finished product. Embodied energy is often used to measure ecological cost.
Energy Star: A labeling system sponsored by the Environmental Protection Agency (EPA) and the US Department of Energy for labeling the most energy-efficient products on the market. It applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. For more information visit the Rating Systems page.
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 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.
Evacuated-tube solar collector: A 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.
Exfiltration: Airflow outward through a wall or building envelope; the opposite of infiltration.
Expanded polysterene (EPS): A 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.
Flat plate collector: A 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. It is typically used for domestic hot water or space heating.
Fly ash: Fine particulates consisting primarily of silica, alumina, and iron that are collected from flue gases during coal combustion. Fly ash 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.
Forest Stewardship Council (FSC): An Independent non-profit 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. FSC certification is done through the use of a third-party certification process. FSC certification includes a chain-of-custody requirement that tracks sustainability of wood products from growth to end use.
Geothermal energy: Hot water or steam extracted from reservoirs beneath the Earth's surface that 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. Synonyms include ground-source heating.
Glazing: 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 (GPF): A term referring to the 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 (HET) is 1.28 gpf.
Greywater: Wastewater from a building that does not include flush-water from toilets (as most commonly defined), but rather water from kitchen sinks or dishwashers. In some places, greywater can be collected and used for alternative uses, namely subsurface irrigation. In autonomous buildings the use of greywater is an important component to reducing energy costs.
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: A 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 above.
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: An independent, non-profit 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.
GreenGuard: A third-party certification program that identifies building products and materials which produce relatively low levels of emissions. GreenGuard is administered by the non-profit 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 multi-family and commercial properties.
Greenwashing: The 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. Synonyms include geothermal energy.
Heat exchanger: A 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 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 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 (HDD): 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.
Home Energy Rating System (HERS): Index or scoring system for energy efficiency established by the Residential Energy Services Network (RESNET) that compares a given home to a 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. The 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. For more information visit the Ratings Page.
Home energy performance audit: An 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.
Heating, ventilation, and air conditioning (HVAC): Collectively, the mechanical systems that heat, ventilate, and cool a building.
Indoor air quality (IAQ): Overall, it is the 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.
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 (ICF): 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.
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.
Inverter: The device used 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.
Life-cycle assessment (LCA): The examination of environmental and health impacts of a product or material over its life cycle. It provides a mechanism for comparing different products and materials for green building.
Light Emitting Diode (LED): 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): LEED for Homes is the oldest U.S. green building program, developed by the United States Green Building Council (USGBC). While this program was initially designed for and applicable to new home projects, renovations, commercial buildings and whole neighborhoods are applicable under other standards. For more information, visit our Rating Systems page.
Low-emissivity coating (Low-e): A very thin metallic coating on glass or plastic window glazing that permits most of the sun's short-wave (visible 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-flow showerhead: Showerhead that restricts water flow to less than the 2.5 gpm limit (at 80 psi) mandated by the U.S. EPA.
Material Safety Data Sheets (MSDS): Forms that include information about chemical and physical hazards, health effects, proper handling, storage, and personal protection appropriate for use of a particular chemical in an occupational environment.
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: The practice of 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. Ultimately this will result in an overall zero consumption of energy.
On-demand hot water: A 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. Conventional hot water heaters have hot water on stand by at all time. On demand water heaters (also called tankless water heaters) are activated by the flow of a hot water valve and instantly heat the hot water as it is being used. This reduces overall energy costs and minimizes heat loss.
Passive heating: A type of 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. Daylighting is an example of passive solar heating.
Passiv Haus 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 Passiv Haus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H (air changes per hour) at 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.
Photovoltaic (PV): The generation of electricity directly from sunlight. A photovoltaic cell has no moving parts. Electrons are energized by sunlight and result in a current flow, thus resulting in electricity.
Porous paving: A paving material that allows rainfall to percolate through and infiltrate the ground. This contrasts to conventional non-porous paving that contributes to stormwater runoff by reducing absorption of water into the ground. Porous paving can be asphalt, concrete or porous grid paver.
R-value: The measure of resistance to heat flow. The higher the R-value, the lower the heat loss. The inverse of U-factor.
Renewable energy: Energy sources that reproduce indefinitely without being significantly depleted. Examples include solar, wind and tidal energy.
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
Strawbale construction: A type of natural building practice that uses strawbales, generally wheat, rice, rye or oat as the insulation and/or primary structural element. This technique is typicallys used in conjunction with timberframing.
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.
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 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.
Trombe wall: A sun-facing wall separated from the outdoors by glazing and an air space that absorbs solar energy during the day and releases it at night through vents at night.
U-factor: Measure of heat conducted through a given product or material-the number of British thermal units (BTU) of heat that move through a square foot of the material in one hour for every one degree Fahrenheit difference in temperature across the material. U-factor is the inverse of R-value.
United States Green Building Council (USGBC): An organization devoted to promoting and certifying green buildings. USGBC created the LEED rating systems. For more information visit the Definitions or Rating Page.
Variable Air Volume (VAV): A method used to control the capacity of heating, cooling and ventilation in an HVAC system. The flow of air, rather than the temperature is calculated. In maintaining a constant air temperature, the air flow rate must fluctuate in order to accomodate the rising and falling heat levels within the thermal zone served.
Volatile Organic Compound (VOC): 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. VOCs are a significant component of greenhouse gas emissions.
Water reclamation: The reuse of water from wastewater treatment in irrigation, land application and other recycling methods.
Window-to-floor ratio: The percentage of total unobstructed window area to the cumulative floor area. This number can be further subdivided by solar orientation in order to calculate passive solar potential.
Xeriscape: A type of efficient landscaping that reduces the need for excessive irrigation. It exemplifies the importance of place-based gardening and land uses in general.