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Absorption Chiller  A water chilling process in which cooling is accomplished by the evaporation of a fluid (usually water), which is then absorbed by a different solution (usually lithium bromide), then evaporated under heat and pressure. The fluid is then condensed with the heat of condensation rejected through a cooling tower.

Adaptability  Design strategy that allows for multiple future uses in a space as needs evolve and change. Adaptable design is considered a sustainable building strategy as it reduces the need to resort to major renovations or tearing down a structure to meet future needs.

Accessory Dwelling Unit (ADU)  A self-contained housing unit incorporated within a single-family dwelling (not within accessory structures, except with a Special Permit) that is clearly a subordinate part of the single-family dwelling.

Adequate Public Facilities  Adequate public facilities ordinances prevent new construction until municipal services, including water, sewer, roads, and schools, are available to serve that development.

Advanced framing techniques  Also called optimum value engineering (OVE), it is a methodology of construction designed to conserve construction materials by using alternate framing methods. Concepts include 19.2-24" framing centers, modular layout, single top plates, individually sized (right-sized) headers or no headers or double rim joists in lieu of headers, framing ladders at T-intersections and open corner framing. Some methods may not work in engineered structures, but many will. The overall savings in framing materials and associated costs can be significant. An excellent website at Toolbase describes the concept in detail.

Affordable Housing  Housing where the occupant is paying no more than 30 percent of gross income for gross housing costs, including utility costs. Housing that is for purchase (with or without rehabilitation) qualifies as affordable housing if it (1) is purchased by a low-income, first-time home buyer who will make the housing his or her principal residence; and (2) has a sale price that does not exceed the mortgages limit for type of single family housing for the area under HUD's single family insuring authority under the National Housing Act.

Agricultural Districts/Preservation Areas  Areas designed to keep land in agriculture that are legally recognized. Landowners may voluntarily enroll in programs and may receive special benefits and protection from regulation.

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

Air Changes Per Hour (ACH)  The movement of a volume of air in a given period of time; if a house has one air change per hour, it means that the air in the house will be replaced in a one-hour period.

Air Change Effectiveness  A measurement of the performance of a ventilation system, by measuring the age of air in a volume. Often accomplished by using a tracer gas decay technique.

Air Cleaning  Indoor-air quality-control strategy to remove various airborne particulates and/or gases from the air. Most common methods are particulate filtration, electrostatic precipitation, and gas sorption.

Air Exchange Rate  The rate at which outside air replaces indoor air in a given space.

Airborne Particulates  Total suspended particulate matter found in the atmosphere as solid particles or liquid droplets. Chemical composition of particulates varies widely, depending on location and time of year. Sources of airborne particulates include dust, emissions from industrial processes, combustion products from the burning of wood and coal, combustion products associated with motor vehicle or non-road engine exhausts, and reactions to gases in the atmosphere.

Air Handling Unit  Equipment that includes a fan or blower, heating and/or cooling coils, regulator controls, condensate drain pans, and air filters.

Air Plenum  Any space used to convey air in a building, furnace, or structure. The space above a suspended ceiling is often used as an air plenum.

Air Pollutant  Any substance in air that could, in high enough concentration, harm man, other animals, vegetation, or material. Pollutants may include almost any natural or artificial composition of airborne matter capable of being airborne. They may be in the form of solid particles, liquid droplets, gases, or in combination thereof. Generally, they fall into two main groups: (1) those emitted directly from identifiable sources, and (2) those produced in the air by interaction between two or more primary pollutants, or by reaction with normal atmospheric constituents, with or without photoactivation. Exclusive of pollen, fog, and dust, which are of natural origin, about 100 contaminants have been identified. Air pollutants are often grouped in categories for ease in classification; some of he categories are: solids, sulfur compounds, volatile organic chemicals, particulate matter, nitrogen compounds, oxygen compounds, halogen compounds, radioactive compound, and odors.

Air Quality Construction Management Plan  A systematic plan for addressing construction practices that can impact air quality during construction and continuing on to occupation.

Alternative Energy  Energy from a source other than the conventional fossil-fuel sources of oil, natural gas and coal (i.e., wind, running water, the sun).

Asbestos  A mineral fiber that can pollute air or water and cause cancer or asbestosis when inhaled. EPA has banned or severely restricted its use in manufacturing and construction.

ASHRAE  The American Society of Heating, Refrigeration and Air Conditioning Engineers writes many of the standards for installation of these systems.

ATSDR  An agency of the US Department of Health and Human Services that maintains a database of information on various toxic materials.

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Bake-out  Process by which a building is heated in an attempt to accelerate VOC emissions from furniture and materials.

Bicycle Storage  Covered and/or secured storage for building occupants commuting by bicycle. This amenity is considered a sustainable building technique in that it encourages human-powered transportation options. Some local governments offer subsidies or incentives to include bicycle storage in an existing or proposed building project.

Bid Specifications  Detailed set of instructions prepared by an architect specifying how a project is to be constructed or renovated and identifying type and quality of materials to be used. The specifications form the basis for soliciting bids from general contractors.

Biological Contamination  Contamination of a building environment caused by bacteria, molds and their spores, pollen, viruses, and other biological materials. It is often linked to poorly designed and maintained HVAC systems. People exposed to biologically contaminated environments may display allergic-type responses or physical symptoms such as coughing, muscle aches and respiratory congestion.

Bioremediation  The cleanup of a contaminated site using biological methods, i.e., bacteria, fungi, plants, etc. Organisms are used to either break down contaminants in soil or water, or accumulate the contaminants in their tissue for disposal. Many bioremediation techniques are substantially less costly than traditional remediation methods using heat, chemical or mechanical means.

Bioretention System  The bioretention system (also referred to as a "rain garden" or a "biofilter") is a stormwater management practice to manage and treat stormwater runoff using a conditioned planting soil bed and planting materials to filter runoff stored within a shallow depression. The method combines physical filtering and adsorption with bio-geochemical processes to remove pollutants. The system consists of an inflow component, a pretreatment element, an overflow structure, a shallow ponding area (less than 9" deep), a surface organic layer of mulch, a planting soil bed, plant materials, and an underdrain system to convey treated runoff to a downstream facility.

Bioswale  A technology that uses plants and soil and/or compost to retain and cleanse runoff from a site, roadway, or other source.

Blackwater  Water that contains animal, human, or food waste.

Brownfields  Abandoned, idled, or under used industrial and commercial facilities/sites where expansion or redevelopment is complicated by real or perceived environmental contamination. They can be in urban, suburban, or rural areas. EPA's Brownfields initiative helps communities mitigate potential health risks and restore the economic viability of such areas or properties.

Building Code  State and local ordinances that prescribe certain minimum health, safety, and performance standards for construction, rehabilitation, or occupancy of housing.

Building Envelope  The exterior surface of a building's construction--the walls, windows, floors, roof, and floor. Also called building shell or buiding enclosure. A building envelope controls heat flow, water vapor flow, rain, groundwater, light and solar radiation, noise and vibrations, contaminants, environmental hazards and odors, insects, rodents and vermin, and fire. It provides strength and rigidity and must be durable.

Building Related Illness  Diagnosable illness whose cause and symptoms can be directly attributed to a specific pollutant source within a building (e.g., Legionnaire's disease, hypersensitivity, pneumonitis). (See sick building syndrome; biological contamination).

Built Environment  The urban environment consisting of buildings, roads, fixtures, parks, and all other improvements that form the physical character of a city.

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Carbon Dioxide Monitoring  A method for determining indoor air quality by using the concentration of carbon dioxide as an indicator. Although the level of CO2 is a good general indicator of air quality, it is reliant on the presence of certain conditions and must be applied accordingly.

Carbon Dioxide Sensor  Device for monitoring the amount of carbon dioxide in an air volume.

Carbon Monoxide (CO)  A colorless, odorless, poisonous gas produced by incomplete fossil fuel combustion.

Cellulose Insulation  Insulation alternative to glass fiber insulation. Cellulose insulation is most often a mixture of waste paper and fire retardant, and has thermal properties often superior to glass fiber. Glass fiber batt insulation often contains formaldehyde, which can adversely affect indoor air quality and human health, and the glass fibers themselves are hazardous if inhaled and irritating to the skin and eyes. Specify cellulose insulation with high recycled content for maximum environmental benefit.

Certified Lumber  General shorthand term for lumber that has been certified sustainable harvest by an independent certification authority. See Forest Stewardship Council.

Charrette  A meeting held early in the design phase of a project, in which the design team, contractors, end users, community stakeholders, and technical experts are brought together to develop goals, strategies, and ideas for maximizing the environmental performance of the project. Research and many projects' experience has indicated that early involvement of all interested parties increases the likelihood that sustainable building will be incorporated as a serious objective of the project, and reduces the soft costs sometimes associated with a green design project.

Chiller  A device that generates a cold liquid that is circulated through an air-handling unit's cooling coil to cool the air supplied to the building.

Chlorofluorocarbons (CFCs)  A family of inert, nontoxic, and easily liquefied chemicals used in refrigeration, air conditioning, packaging, insulation, or as solvents and aerosol propellants. Because CFCs are not destroyed in the lower atmosphere they drift into the upper atmosphere where their chlorine components destroy ozone.

Cistern  Small tank or storage facility used to store water for a home or farm; often used to store rainwater.

Cluster Development  Development design that concentrates buildings and infrastructure in specific areas on a site to allow remaining land to be used for recreation, common open space, or the preservation of historical or environmentally sensitive features.

Combined Heat and Power (CHP) or Co-Generation  CHP or co-generation is the simultaneous production of power and usable heat.

Comfort  An important design objective in sustainable building. Designing for comfort aims to create a space where people enjoy being; such qualitative, performance-based objectives are a hallmark of sustainable building.

Commissioning (Building)  The process of ensuring installed systems function as specified, performed by a third party commissioning agent. Elements to be commissioned are identified, installation is observed, sampling is conducted, test procedures are devised and executed, staff training is verified, and operations and maintenance manuals are reviewed.

Community  A factor with increased emphasis in sustainable building and sustainable development. Design and building related practices enhancing and supporting community ideals and functions are considered more sustainable than those that do not, all else being equal.

Community Development Corporation (CDC)  Non-profit groups accountable to local residents that engage in a wide range of physical, economic and human development activities. CDCs rebuild their communities through housing, commercial, job development and other activities. A CDC's mission is normally focused on serving the local needs of low- or moderate-income households. Resident control usually takes the form of board representation.

Community Housing Development Corporation (CHDO)  A private, non-profit development corporation that that meets a series of qualifications prescribed in the HOME regulations and has been designated by the local Participating Jurisditcion (city, county or state) to receive a set-aside of HOME program funds (see HOME below). 1/3 of the CHDO's board must represent low-income households. A participating jurisdiction must award at least 15 percent of its annual HOME allocation to CHDOs. CHDOs may own, develop, or sponsor HOME-financed housing.

Compact Fluorescent Lamp (CFL)  Small fluorescent lamps used as more efficient alternatives to incandescent lighting. Also called PL, CFL, Twin-Tube, or BIAX lamps.

Composting  Controlled biological decomposition of organic material in the presence of air to form a humus-like material that can be used as organic fertilizer. Controlled methods of composting include mechanical mixing and aerating, ventilating the materials by dropping them through a vertical series of aerated chambers, or placing the compost in piles out in the open air and mixing it or turning it periodically.

Comprehensive Plan  Regional, state, or local documents that describe community visions for future growth. Comprehensive plans describe general plans and policies for how communities will grow and the tools that are used to guide land use decisions, and give general, long-range recommendations for community growth. Typical elements include, land use, housing, transportation, environment, economic development, and community facilities.

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

Construction and Demolition Waste  Waste building materials, dredging materials, tree stumps, and rubble resulting from construction, remodeling, repair, and demolition of homes, commercial buildings and other structures and pavements. May contain lead, asbestos, or other hazardous substances.

Construction Waste Management  General term for strategies employed during construction and demolition to reduce the amount of waste and maximize reuse and recycling. Construction waste management is a sustainable building strategy in that it reduces the disposal of valuable resources, provides materials for reuse and recycling, and can promote community industries.

Cooling Load  The hourly amount of heat that must be removed from a building to maintain indoor comfort (measured in British thermal units [Btu]).

Cool Roof  Specialized roofing materials designed to reflect the heat of the sun away from the building, thus reducing the cooling load and associated air conditioning costs. There are various manufacturers of cool roofs.

Cooling Tower  Device which dissipates the heat from water-cooled systems by spraying the water through streams of rapidly moving air.*  Cooling towers can be substantial water users, and provide an opportunity for water conservation. Many local water providers can supply technical information on water use reduction and may provide incentives for measures with substantial water savings.

Cost-Benefit Analysis  A decision-making tool that allows a comparison of options based on the level of benefit derived and the cost to achieve the benefit from different alternatives.

Cradle-to-Cradle  A term used in life-cycle analysis to describe a material or product that is recycled into a new product at the end of its defined life.

Cradle-to-Grave  A term used in life-cycle analysis to describe the entire life of a material or product up to the point of disposal. Also refers to a system that handles a product from creation through disposal.

Cubic Feet Per Minute (CFM)  A measure of the volume of a substance flowing through air within a fixed period of time. With regard to indoor air, refers to the amount of air, in cubic feet, that is exchanged with outdoor air in a minute's time; i.e., the air exchange rate.

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Daylight Sensor  see Photocell.

Daylighting  Using natural light in an interior space to substitute for artificial light. Daylighting is considered a sustainable building strategy in that it can reduce reliance on artificial light (and reduce energy use in the process) and when well designed, contributes to occupant comfort and performance.

Degree-Day  A rough measure used to estimate the amount of heating required in a given area; is defined as the difference between the mean daily temperature and 65 degrees Fahrenheit. Degree-days are also calculated to estimate cooling requirements.

Demand Hot Water System  Hot water heaters designed to provide instantaneous hot water, rather than storing preheated hot water in a tank. Such devices can serve an entire home, or be "point-of-use", serving an individual water use. Benefits include elimination of "standby losses", or energy wasted keeping stored water warm, and with point of use devices, reduction or elimination of water wasted waiting for water to get warm, as well as conductive losses as water travels through pipes. Electric demand systems tend to use a large amount of energy; gas-fired units with standing pilot lights lose much of their efficiency due to the ongoing pilot light.

Density  The average number of people, families, or housing units on one unit of land. Density is also expressed as dwelling units per acre.

Density bonus  Allows developers to build in specified areas densities that are higher than normally allowed.

Depressurization  A condition that occurs when the air pressure inside a structure is lower that the air pressure outdoors. Depressurization can occur when household appliances such as fireplaces or furnaces, that consume or exhaust house air, are not supplied with enough makeup air. Radon may be drawn into a house more rapidly under depressurized conditions. Backdrafting of furnaces and vented appliances can also occur with depressurization, introducing exhaust gases into the house.

Desiccant Cooling/Dehumidification  The use of chemical (or physical) absorption of water vapour to dehumidify air and reduce the latent cooling load in a building HVAC system. Air conditioning systems are sized for a combination of two cooling loads: sensible (cooling of space air) and latent (air humidity), which can account for as much as 30% to 50%. Desiccant dehumidification removes humidity from ventilation air, allowing and smaller air-conditioners and air-handling systems to meet the remaining sensible cooling load. Reducing humidity improves indoor air quality by preventing condensation in equipment and mitigating the effects of allergens. There are two types of desiccant systems, liquid (sorbent) and dry.

Displacement Ventilation  Ventilation that uses natural convection processes to move warm air up and out of a volume. Displacement ventilation tends to use less energy than conventional forced air ventilation, as it works with natural convection processes.

Distributed Generation  Distributed generation typically refers to distributed electricity generating technologies (and sometimes heat and power technologies) that are embedded in the local distribution system, either behind the customer meter as in a net metering installation or selling directly into the grid (as in a small independent power producer).

District Energy System  District energy is an approach to supplying thermal energy in the form of steam, hot water and cold water through a distribution system of pipe from a central plant to individual users. Users then extract the energy from the distribution system for their individual heating, cooling and process requirements.

Drainage Plane  A set of water repellent materials (building paper, housewrap, foam insulation, etc.) designed and constructed to drain water. It is interconnected with flashings, window and door openings, and other penetrations of the building enclosure to provide drainage of water to the exterior of the building. The materials that form the drainage plane overlap each other shingle fashion or are sealed so that water flow is downward and outward.

Dual flush toilet  These toilets have two different settings, usually 0.8 gallons for liquid removal and 1.6 gallons for full flush solid removal. On the average they use about 2,500 gallons per year, compared to a 1.6 single flush that uses about 4,500 gallons per year.

Durability  A factor that affects the life cycle performance of a material or assembly. All other factors being equal, the more durable item is environmentally preferable, as it means less frequent replacement. However, durability is rendered moot as a factor if the material is replaced for aesthetic reasons prior to it actually wearing out.

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EIFS (external insulation finishing system)  A combination of insulation and stucco system cladding for buildings. There are two types of EIFS available in the U.S.--barrier systems and drainable systems.

Embodied Energy  The total amount of energy used to create a product, including energy expended in raw materials extraction, processing, manufacturing and transportation. Embodied energy is often used as a rough measure of the environmental impact of a product.

Encapsulation  The treatment of asbestos-containing material with a liquid that covers the surface with a protective coating or embeds fibers in an adhesive matrix to prevent their release into the air.

Energy Modeling  Process to determine the energy use of a building based on software analysis. Also called building energy simulation. Common simulation software are DOE-2 and Energy Plus.

Energy Star  A voluntary labeling program of the U.S. Environmental Protection Agency to identify and promote energy-efficient products. Originally designed for computers and monitors, it has now expanded to include office products, major appliances, lighting, home electronics and more. Additional programs certify complete buildings homes, commercial, and industrial.

Engineered Lumber/Wood  Composite wood products made from lumber, fiber or veneer, and glue. Engineered wood products can be environmentally preferable to dimensional lumber, as they allow the use of waste wood and small diameter trees to produce structural building materials. Engineered wood products distribute the natural imperfections in wood fiber over the product, making them stronger than dimensional lumber. This allows for less material to be used in each piece, another environmental benefit. Potential environmental drawbacks with engineered wood include impacts on indoor environmental quality due to offgassing of chemicals present in binders and glues, and air and water pollution related to production.

Environmental Footprint  For an industrial setting, this is a company's environmental impact determined by the amount of depletable raw materials and nonrenewable resources it consumes to make its products, and the quantity of wastes and emissions that are generated in the process. Traditionally, for a company to grow, the footprint had to get larger. Today, finding ways to reduce the environmental footprint is a priority for leading companies.*  An environmental footprint can be determined for a building, city, or nation as well, and gives an indication of the sustainability of the unit.

EPA  The U.S. Environmental Protection Agency is the federal agency charged with the oversight and development of environmental regulations and programs. The EPA also oversees important research and public information and education activities.

Erosion  The wearing away of land surface by wind or water, intensified by land-clearing practices related to farming, residential or industrial development, road building, or logging.*  

Externality  An externality is an effect of a purchase or use decision by one set of parties on others who did not have a choice and whose interests were not taken into account. The non-consenting parties may be either helped (by external benefits) or harmed (by external costs) by the decision.

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Finger-jointed studs  Often the lumber being cut today is a shadow of the old-growth lumber of yesterday in quality, density and overall suitability for construction. However, by conserving the shorter sections of lumber and removing the undesirable wane and knots, these sections can be fitted with special splicing techniques to form longer and more dimensionally stable lumber. The application is usually limited to vertical installation because of this splicing technique.

First cost  The sum of the initial expenditures involved in capitalizing a property; includes items such as transportation, installation, preparation for service, as well as other related costs.

Flow reducer  A device attached either just downstream from the water shutoff valve to a building or at the outlet of a fixture designed to reduce or limit the amount of water flow in relation to the delivery pressure from the street. Flow reducers can cut the flow of water dramatically, saving thousands of gallons each year in a dwelling or even more in larger buildings. Flow reducers are never installed on automatic fire extinguishing systems for obvious reasons.

Flush-Out  A period after finish work and prior to occupation that allows the building's materials to cure and release volatile compounds and other toxins. A building flush-out procedure is normally followed, with specified time periods, ventilation rate, and other criteria.

Fly Ash  A fine, glass-powder recovered from the gases of burning coal during the production of electricity. These micron-sized earth elements consist primarily of silica, alumina and iron. When mixed with lime and water the fly ash forms a cementitious compound with properties very similar to that of portland cement. Because of this similarity, fly ash with a low LOI (carbon content) can be used to replace a portion of cement in the concrete, providing some distinct quality advantages. The concrete is denser resulting in a tighter, smoother surface with less bleeding. Fly ash concrete offers a distinct architectural benefit with improved textural consistency and sharper detail. Regulations vary from state to state, however, ASTM suggests that fly ash must not contain more than 6% unburned carbon to be used for its cementitious qualities. Otherwise, concrete companies use it as a fine aggregate in concrete block. Others use it for filling old coal mines, seaside docking areas and as a lining for hazardous waste dumps. Substitution of fly ash for portland cement in concrete is considered a sustainable building strategy, as it reduces the amount of energy-intensive (and CO2-producing) cement in the mix, as well as providing the performance enhancements described above.

Footprint (Building)  The area of a building formed by the perimeter of the foundation. Shrinking the footprint of a building allows for more open space and pervious surface on a site.

Footprint (Environmental)  See Environmental Footprint

Forest Stewardship Council (FSC)  A third-party certification organization, evaluating the sustainability of forest products. FSC-certified wood products have met specific criteria in areas such as forest management, labor conditions, and fair trade.

Formaldehyde  A colorless, pungent, and irritating gas, CH20, used chiefly as a disinfectant and preservative and in synthesizing other compounds like resins.

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Geothermal/Ground Source Heat Pump  These heat pumps are underground coils to transfer heat from the ground to the inside of a building. (See heat pump; water source heat pump) 1 This type of heat pump can realize substantial energy savings over conventional heat pumps, by using the naturally more stable temperature of the earth as its heat source.

Global Warming  An increase in the near surface temperature of the earth. Global warming has occurred in the distant past as the result of natural influences, but the term is most often used to refer to the warming predicted to occur as a result of increased emissions of greenhouse gases. Scientists generally agree that the earth's surface has warmed by about 1 degree Fahrenheit in the past 140 years. The Intergovernmental Panel on Climate Change (IPCC) recently concluded that increased concentrations of greenhouse gases are causing an increase in the earth's surface temperature and that increased concentrations of sulfate aerosols have led to relative cooling in some regions, generally over and downwind of heavily industrialized areas.

Glazing  Translucent or transparent element of a window assembly. Glazing can have properties that increase its thermal performance, including Low-Emissivity coatings, multiple panes, thermally broken spacers, etc.

Global Warming Potential  The ratio of the warming caused by a substance to the warming caused by a similar mass of carbon dioxide. CFC-12, for example, has a GWP of 8,500, while water has a GWP of zero.

Gray Water  See Greywater.

Green Building  (1) A building that conforms to environmentally sound principles of construction practices, resource use and operations. (2) The process of designing and construction such a building.

Green Cleaning Practice  A term to describe the process of cleaning with environmentally-friendly, non-toxic, biodegradable products. Green cleaning avoids chemically-reactive and toxic cleaning products which contain various toxic chemicals, some of which emit volatile organic compounds (VOCs) causing respiratory and dermatological problems among other adverse effects.

Green Design  A design, usually architectural, conforming to environmentally sound principles of building, material and energy use. A green building, for example, might make use of solar panels, skylights and recycled building materials.

Green Label  A certification program by the Carpet and Rug Institute for carpet and adhesives meeting specified criteria for release of volatile compounds.

Green Roof  Contained green space on, or integrated with, a building roof. Green roofs maintain living plants in a growing medium on top of a membrane and drainage system. Green roofs are considered a sustainable building strategy in that they have the capacity to reduce stormwater runoff from a site, modulate temperatures in and around the building, and have thermal insulating properties. On large walkable roofs, pleasing garden atmospheres can be created, and watering requirements can be reduced by the installation of stormwater-recovery systems.

Greenfields  Newly developed commercial real estate on what was previously undeveloped open space.

Greenhouse Effect  The warming of the Earth's atmosphere attributed to a buildup of carbon dioxide or other gases; some scientists think that this build-up allows the sun's rays to heat the Earth, while making the infra-red radiation atmosphere opaque to infra-red radiation, thereby preventing a counterbalancing loss of heat.

Greenhouse Gas  A gas, such as carbon dioxide or methane, which contributes to potential climate change.

Greywater  Waste water from lavatories, showers, baths and sinks only. This water can be stored in special equipment and may then be used to water lawns, gardens or other relatively benign non-potable uses such as toilet flushing or groundwater recharge. Gray water reuse is restricted in many jurisdictions; check with local health and building officials. Water from toilets is called black water; it must be properly drained to the sewer or septic system.

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Halogen  A type of incandescent lamp with higher energy-efficiency that standard ones.

Hard Costs  The direct costs to construct a building, also known as "bricks and mortar" costs, as distinguished from legal, financing, architectural and other fees required for the project.

Heat Exchanger  Device for exchanging heat present in wastewater or stale air to preheat incoming water or air. See Heat Recovery Ventilator for more information on air-to-air heat exchangers.

Heat Island Effect  A "dome" of elevated temperatures over an urban area caused by structural and pavement heat fluxes and pollutant emissions. The effect increases the need for cooling energy and can exacerbate pollution problems (reduced winter heating demands are less significant). Heat islands can be effectively reduced by shading streets with trees and improving the urban forest overall.

Heat Pump  An electric device with both heating and cooling capabilities. It extracts heat from one medium at a lower (the heat source) temperature and transfers it to another at a higher temperature (the heat sink), thereby cooling the first and warming the second. (See geothermal, water source heat pump.)

Heat Recovery Unit/Ventilator  An air-to-air heat exchanger with balanced exhaust and supply fans that meet all necessary ventilation needs without producing drafts or air pressure imbalance on a heating or cooling system.

High Efficiency  General term for technologies and processes that require less energy, water, or other inputs to operate. A goal in sustainable building is to achieve high efficiency in resource use when compared to conventional practice. Setting specific targets in efficiency for systems (e.g., using only EPA Energy Star certified equipment, furnaces with an AFUE rating above 90%, etc.) and designs (e.g., watts per square foot targets for lighting) help put this general goal of efficiency into practice.

High-Heeled Truss  Roof truss design that allows space for insulation near the eaves. Conventional truss design limits the amount of insulation that can be applied in this area.

High Performance Glazing  Generic term for glazing materials with increased thermal efficiency.

Household Hazardous Waste  Hazardous products used and disposed of by residential as opposed to industrial consumers. Includes paints, stains, varnishes, solvents, pesticides, and other materials or products containing volatile chemicals that can catch fire, react or explode, or that are corrosive or toxic.

Housing Element  A comprehensive assessment of current and projected housing needs for all economic segments of the community. It sets forth local housing policies and programs to implement those policies.

HVAC (Heating, Ventilation, and Air Conditioning)  General term for the heating, ventilation and air conditioning system in a building. System efficiency and design impact the overall energy performance of a home and its indoor environmental quality.

Hydronic Radiant Heating (Hydronic System)  A space heating system that uses water circulated through a radiant floor or baseboard system or a convection or fan coil system.

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Impact Fees  Costs imposed on new development to fund public facility improvements required by new development and ease fiscal burdens on localities.

Imperviousness Overlay Zoning  One form of the overlay zoning process. Environmental aspects of future imperviousness are estimated based on the future zoning build-out conditions. Estimated impacts are compared with environmental protection goals to determine the limit for total impervious surfaces in the watershed. Imperviousness overlay zoning areas are then used to define subdivision layout options that conform to the total imperviousness limit.

Impervious Surface  Any surface through which rainfall cannot pass or be effectively absorbed. (Roads, buildings, paved parking lots, sidewalks etc.) Impervious surfaces can lead to excessive stormwater runoff and limit the amount of stormwater that remains onsite or recharges local aquifers.

Incentive Zoning  Provides for give and take compromise on zoning restrictions, allowing for more flexibility to provide environmental protection. Incentive zoning allows a developer to exceed a zoning ordinance's limitations if the developer agrees to fulfill conditions specified in the ordinance. The developer may be allowed to exceed height limits by a specified amount in exchange for providing open spaces or plazas adjacent to the building.

Inclusionary zoning  A system that requires a minimum percentage of lower and moderate income housing to be provided in new developments. Inclusionary programs are based on mandatory requirements or development incentives, such as density bonuses.

Indigenous Planting  Landscaping strategy that uses native plants. Provided the natives are placed in the proper growing conditions; such plantings can have low, or zero supplemental water needs.

Indoor Air Pollution  Chemical, physical, or biological contaminants in indoor air.

Indoor Air Quality (IAQ)  ASHRAE defines acceptable indoor air quality as air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which 80% or more people exposed do not express dissatisfaction.

Infill Development  Infill projects use vacant or underutilized land in previously developed areas for buildings, parking, and other uses.

Infiltration  The penetration of water through the ground surface into sub-surface soil or the penetration of water from the soil into sewer or other pipes through defective joints, connections, or manhole walls. b. The entrance of exterior unconditioned air through various means into a building. Under the older codes, a dwelling generally had the equivalent of a 4-foot-diameter hole in infiltration leakage. While newer buildings greatly improve this leakage, other problems such as poor indoor air quality and transpiration of moisture to internal stud bays now occurs and must be remedied with such items as air-to-air exchangers and specialized waterproofing techniques.

Infrastructure  Water and sewer lines, roads, urban transit lines, schools and other public facilities needed to support developed areas.

Insulated Concrete Form  Expanded foam forms that are left in place after the concrete is poured for a foundation or wall. The foam increases the thermal performance of the structure over non-insulated concrete.. The panels, made of expanded polystyrene foam (EPS), high-density polyethylene (HDPE), polyvinyl chloride (PVC) or polycarbonate (PC), are usually pre-engineered and produce a fire resistive barrier up to 4-hour rated.

Integrated Pest Management (IPM)  A mixture of chemical and other, non-pesticide, methods to control pests.

Integrated Waste Management  The complementary use of a variety of practices to handle solid waste safely and effectively. Techniques include source reduction, recycling, composting, combustion and landfilling.

Integration  An essential concept in sustainable building. Viewing a building as a system allows the discovery of synergies and potential tradeoffs or pitfalls with design choices. An integrated design approach helps maximize synergies and minimize unintended consequences.

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Land Use  The manner in which a parcel of land is used or occupied.

Lead (Pb)  A heavy metal that is hazardous to health if breathed or swallowed. Its use in gasoline, paints, and plumbing compounds has been sharply restricted or eliminated by federal laws and regulations.

LEED  A self-assessing green building rating system developed by the U.S. Green Building Council. LEED™ stands for Leadership in Energy and Environmental Design, and evaluates a building from a systems perspective. By achieving points in different areas of environmental performance, a building achieves a level of "certification" under the system. Specialized LEED methodologies have been developed for commercial buildings, homes, schools, renovations, neighborhoods, and other building types.

Life Cycle (of a Product)  All stages of a product's development, from extraction of raw materials and fuel for transport to production, marketing, use, and disposal.

Life Cycle Assessment/Analysis (LCA)  The assessment of a product's full environmental costs, from raw material to final disposal, in terms of consumption of resources, energy, and waste. Life cycle analysis is used as a tool for evaluating the relative performance of building materials, technologies, and systems.

Life Cycle Costing  A process to determine the sum of all the costs associated with an asset or part thereof, including acquisition, installation, operation, maintenance, refurbishment and disposal costs. It is therefore pivotal to the asset management process. Life Cycle Costing incorporates both Life Cost Planning which occurs during development or manufacture and implementation of that plan by Life Cost Analysis as the asset is used or occupied. Life Cycle Costing forms an input to evaluation processes such as Value Management, Economic Appraisal and Financial Appraisal.

Light-Emitting Diode (LED)  A long-lasting illumination technology used for exit signs which requires very little power.

Light Shelf  A horizontal shelf positioned (usually above eye level) to reflect daylight onto the ceiling and to shield direct flare from the sky.

Linoleum  A resilient flooring product developed in the 1800s, manufactured from cork flour, linseed oil, oak dust, and jute. Linoleum's durability, renewable inputs, anti-static properties, and easy-to-clean surface often make it classified as a "green" building material.

Local/Regional Materials  Building products manufactured and/or extracted within a defined radius of the building site. For example, the US Green Building Council defines local materials as those that are manufactured, processed and/or extracted within a 500-mile radius of the site. Use of regional materials is considered a sustainable building strategy due to the fact that these materials require less transport, reducing transportation-related environmental impacts. Additionally, regional materials support local economies, supporting the community goal of sustainable building.

Location Efficient Mortgage  A lending program that allows homebuyers to borrow more money based on the transportation cost savings of living near mass transit.

Low Emissivity (low-E) Windows  Window technology that lowers the amount of energy loss through windows by inhibiting the transmission of radiant heat while still allowing sufficient light to pass through.

Low Impact Development (LID)  An approach to environmentally friendly land use planning. It includes a suite of landscaping and design techniques that attempt to maintain the natural, pre-developed ability of a site to manage rainfall. LID techniques capture water on site, filter it through vegetation, and let it soak into the ground where it can recharge the local water table rather than being lost as surface runoff. An important LID principle includes the idea that stormwater is not merely a waste product to be disposed of, but rather that rainwater is a resource.

Low Income  A household or family whose annual (gross) income does not exceed 80 percent of the median income for the area (adjusted for family size). A household or family whose annual (gross) income does not exceed 50 percent of the median income for the area is "very low income."

Low-Income Housing Tax Credit (LIHTC) Tax incentive created in the Tax Reform Act of 1986 that is designed to attract equity capital for investment in rent restricted affordable housing. The program encourages the production of affordable housing by offering its owners tax credits for a ten year period based on the cost of development and the number of low income units produced.

Low VOC  Building materials and finishes that exhibit low levels of "offgassing," the process by which VOCs (Volatile Organic Compounds) are released from the material, impacting health and comfort indoors and producing smog outdoors. Low (or zero) VOC is an attribute to look for in an environmentally preferable building material or finish. See "Volatile Organic Compound (VOC)" for more information.

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Maintenance  An overlooked element of a product, system, or design strategy that impacts cost over the life cycle. Selecting products and designing for easy maintenance enhances durability and lessens the likelihood that maintenance is overlooked. Establishing and adhering to a maintenance protocol ensures that materials and systems function to specifications.

Master Plan  A statement, through text, maps, illustrations or other forms of communication, that is designed to provide a basis for decision making regarding the long term physical development of the municipality.

Material Safety Data Sheet (MSDS)  A compilation of information required under the OSHA Communication Standard on the identity of hazardous chemicals, health, and physical hazards, exposure limits, and precautions. Section 311 of SARA requires facilities to submit MSDSs under certain circumstances.

MDF (Medium Density Fiberboard)  A composite wood fiberboard, used for cabinetry and other interior applications. MDF containing urea formaldehyde can contribute to poor indoor air quality.

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

Mercury  A metal that is an odorless silver liquid at room temperature, converting to an odorless, colorless gas when heated. Mercury readily combines with other elements, and accumulates in the environment. Mercury is toxic, and causes a range of neurological, organ, and developmental problems. Fluorescent lights and old thermostats are two building related products that can contain significant amounts of mercury. Newer fluorescent lights are available with substantially reduced amounts of mercury.

Mixed Use Development  Development that is created in response to patterns of separate uses that are typical in suburban areas necessitating reliance on cars. Mixed use developments include residential, commercial, and business accommodations in one area.

Modular Building  Building technique using modular, or pre-constructed components. Building on a "module" also refers to the concept of using standardized dimensions that reduce the amount of construction waste. Building in four-foot increments is one strategy.

Montreal Protocol  Treaty, signed in 1987, governs stratospheric ozone protection and research, and the production and use of ozone-depleting substances. It provides for the end of production of ozone-depleting substances such as CFCs. Under the Protocol, various research groups continue to assess the ozone layer. The Multilateral Fund provides resources to developing nations to promote the transition to ozone-safe technologies.

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Natural Ventilation  Ventilation design that uses existing air currents on a site and natural convection to move and distribute air through a structure or space. Strategies include placement and operability of windows and doors, thermal chimneys, landscape berms to direct airflow on a site, and operable skylights.

Night Flushing  The process of removing hot air from a building during the cool evening hours, to cool elements with thermal mass within the building and flush stale air.

Non-Point Source Pollution (NPS)  Pollution that cannot be identified as coming from a specific source and thus cannot be controlled through the issuing of permits. Storm water runoff and some deposits from the air fall into this category.

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Occupancy Sensor  A sensing device, commonly connected to a room's lighting but also occasionally to heating or ventilation, that shuts down these services when the space is unoccupied.

Offgassing  Release of volatile chemicals from a product or assembly. Many chemicals released from materials impact indoor air quality and occupant health and comfort. Offgassing can be reduced by specifying materials that are low- or no-VOC and by avoiding certain chemicals (e.g., urea formaldehyde) entirely. Controlling indoor moisture, and specifying pre-finished materials, can also reduce offgas potential.

On-Demand Hot Water  See Demand Hot Water Systems

On-Site Stormwater Management  Building and landscape strategies to control and limit stormwater pollution and runoff. Usually an integrated package of strategies, elements can include vegetated roofs, compost-amended soils, pervious paving, tree planting, drainage swales, and more.

Operations Manual (O&M Manual)  Manual developed to assist building occupants in maintaining and operating a green building and its features. Many features' effectiveness can be reduced or eliminated by the actions (or inaction) of occupants and maintenance crews. An operations manual usually includes product and system information and warranties, contact information, and other information required for effective operations and maintenance.

Orientation (Solar)  Orientation of a structure for controlled solar gain is essential to the success of passive and active solar design elements. Sun charts and software assist in orienting a building for maximum solar benefit. Designing for solar considerations can substantially reduce both heating and cooling.

OSB  Oriented Strand Board. A high strength, structural wood panel formed by binding wood strands with resin in opposing orientations. OSB is environmentally beneficial in that it uses small dimension and waste wood for its fiber; however, resin type should be considered for human health impact, and the production process monitored for air pollutant emissions.

Overhangs  Architectural elements on roofs and above windows that function to protect the structure from the elements or to assist in daylighting and control of unwanted solar gain. Sizing of overhangs should consider their purpose, especially related to solar control.

Overlay Districts  Zoning districts in which additional regulatory standards are superimposed on existing zoning. Overlay districts provide a method of placing special restrictions in addition to those required by basic zoning ordinances.

Ozone (O3)  A naturally occurring, highly reactive, irritating gas comprising triatomic oxygen formed by recombination of oxygen in the presence of ultraviolet radiation. This gas builds up in the lower atmosphere as smog pollution, while in the upper atmosphere it forms a protective layer that shields the earth and its inhabitants from excessive exposure to damaging ultraviolet radiation.

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Passive Solar  Strategies for using the sun's energy to heat (or cool) a space, mass, or liquid. Passive solar strategies use no pumps or controls to function. A window, oriented for solar gain and coupled with massing for thermal storage (e.g., a Trombe wall) is an example of a passive solar technique.

Patient Equity  Equity whose returns on investment are received on a long-term timeframe, complementing and supplementing typical short-term real estate financing. These may include investments from foundations and pension funds, revenue from parking facilities, and other sources of capital.

Performance Bond  A surety bond between two parties, insuring one party, the building owner/developer/purchaser, against loss if the terms of a contract are not fulfilled by the other party, the contractor/seller. Usually part of a construction contract or supply agreement.

Performance Zoning  Establishes minimum criteria to be used when assessing whether a particular project is appropriate for a certain area; ensures that the end result adheres to an acceptable level of performance or compatibility. This type of zoning provides flexibility with the well-defined goals and rules found in conventional zoning.

Permeable paving  See Porous Paving

Photocell  A device that measures the amount of incident light present in a space.

Photovoltaic (PV) Cell  An electronic device consisting of layers of semiconductor materials fabricated to form a junction (adjacent layers of materials with different electronic characteristics) and electrical contacts and being capable of converting incident light directly into electricity (direct current).

Photovoltaic (PV) Module  An integrated assembly of interconnected photovoltaic cells designed to deliver a selected level of working voltage and current at its output terminals, packaged for protection against environment degradation, and suited for incorporation in photovoltaic power systems.

Phytoremediation  Low-cost option for site cleanup when the site has low levels of contamination that are widely dispersed. Phytoremediation (a subset of bioremediation) uses plants to break down or uptake contaminants.

Porous Paving  Paving surfaces designed to allow stormwater infiltration and reduce runoff. Several methods are commonly used, including spaced pavers with soil infill and newer specialized asphalt and concrete applications that actually allow rainwater to pass through them.

Precautionary Principle  When information about potential risks is incomplete, basing decisions about the best ways to manage or reduce risks on a preference for avoiding unnecessary health risks instead of on unnecessary economic expenditures.

Public Benefits Charge  A charge added to a customer billing which is intended to cover costs related to services that a utility provides in the public interest. A utility may be mandated by legislation or regulations to provide some or all of the services covered by this charge, and these services range from educational initiatives to funding for low-income customers to environmental programs.

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Radiant Heat  Heat transferred in the form of light energy (including non-visible spectra). Distinct from conductive heat, occurring with the direct contact between two materials.

Radiant barrier roof sheathing  Usually a foil-faced plywood, manufactured with proprietary methods and used as the roof sheathing under the roofing material itself. The reflective surface of the material actually reflects heat away from the roof back through the shingles without significantly increasing the thermal load on the material (usually only 2 to 5 degrees). Other methods are rolled materials that are applied after the regular plywood or OSB sheathing. Both materials can reduce attic and subsequent living area cooling loads significantly. Some manufacturers claim up to 97 percent effectiveness.

Radon  A colorless naturally occurring, radioactive, inert gas formed by radioactive decay of radium atoms in soil or rocks. Design strategies help reduce the amount of radon infiltration into a building and remove the gas that does infiltrate.

Rainwater Catchment/Harvest  On-site rainwater harvest and storage systems used to offset potable water needs for a building and/or landscape. Systems can take a variety of forms, but usually consist of a surface for collecting precipitation (roof or other impervious surface) and a storage system. Depending on the end use, a variety of filtration and purification systems may also be employed.

Recharge  Water that infiltrates into the ground, usually from above, that replenishes groundwater reserves, provides soil moisture, and affords evapotranspiration.

Recycled Content  The content in a material or product derived from recycled materials versus virgin materials. Recycled content can be materials from recycling programs ("post-consumer") or waste materials from the production process or an industrial/agricultural source ("pre-consumer" or "post-industrial").

Recycling  Process by which materials that would otherwise become solid waste are collected, separated or processed and returned to the economic mainstream to be reused in the form of raw materials or finished goods.

Recycling Areas  Space dedicated to recycling activities is essential to a successful recycling program, both on the construction site and in the building after occupation. For strategies related to determining recycling area configuration and placement, see the Business and Industry Resource Venture site.

Recycling Bins  Containers to temporarily hold recyclable materials until transferred to a larger holding facility of pick-up by a recycling service. Conveniently located bins increase recycling rates by allowing occupants to recycle more easily. Designing space for recycling bins is a physical reminder of a commitment to recycling.

Re-entry  (In indoor air program) Refers to air exhausted from a building that is immediately brought back into the system through the air intake and other openings.

Refurbished  Products that have been upgraded to be returned to active use in their original form. Refurbishing is considered a form of reuse, and is preferable to recycling as it requires less processing and inputs to return a product to useful service.

Regional Manufacture  Goods produced within a certain radius of the project site. Using regionally produced goods is considered a sustainable building strategy in that it reduces the transportation impacts associated with the product, it often allows for a better understanding of the production process and increases the likelihood that the product was manufactured in accordance with environmental laws, and it supports regional economies.

Relative Humidity  Ratio of the amount of water vapor in air at a specific temperature to the maximum capacity of the air at that temperature.

Renewable Resources  A resource that can be replenished at a rate equal to or greater than its rate of depletion; e.g., solar, wind, geothermal and biomass resources.

Renovation  Upgrade of an existing building or space that maintains the original structure of a building.

Resource Conservation  Practices that protect, preserve or renew natural resources in a manner that will ensure their highest economic or social benefits.

Retrocommissioning  Refers to the systematic process of commissioning of existing buildings for identifying and implementing operational and maintenance improvements and for ensuring their continued performance over time. It is an inclusive and systematic process that intends not only to optimize how equipment and systems operate, but also to optimize how the systems function together.

Reuse  Using a product or component of municipal solid waste in its original form more than once; e.g., refilling a glass bottle that has been returned or using a coffee can to hold nuts and bolts.*  Reuse is a sustainable building strategy in that it reduces the strain on both renewable and nonrenewable resources, and when materials are reused on or near the site of salvage, they reduce transportation-related environmental impacts.

Revolving Fund  A fund established to finance a cycle of operations to which reimbursements and collections are returned for reuse in a manner such as will maintain the principal of the fund, e.g., working capital funds, industrial funds, and loan funds.

Risk Assessment  Qualitative and quantitative evaluation of the risk posed to human health and/or the environment by the actual or potential presence and/or use of specific pollutants. Risk Factor Characteristics (e.g., race, sex, age, obesity) or variables (e.g., smoking, occupational exposure level) associated with increased probability of a toxic effect.

Runoff  The water that flows off the surface of the land, ultimately into our streams and water bodies, without being absorbed into the soil.

R-value  A measure of resistance to heat flow or conductivity for a material, especially insulation; the reciprocal of U-factor. While many in the building community consider R-value to be the primary or paramount indicator of energy efficiency, it only accounts for conduction, one of three modes of heat flow, (the other two being convection and radiation).

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Salvage  Building materials diverted from the waste stream intended for reuse.

Sick Building Syndrome  Building whose occupants experience acute health and/or comfort effects that appear to be linked to time spent therein, but where no specific illness or cause can be identified. Complaints may be localized in a particular room or zone, or may spread throughout the building.

Shower Facilities  In buildings that house workers, shower facilities are considered a green building feature in that they allow occupants that elect to travel by bicycle and other human powered modes of transportation to exercise this option.

Site Plan  A scaled plan showing proposed uses and structures for a parcel of land. A site plan could also show the location of lot lines, the layout of buildings, open space, parking areas, landscape features, and utility lines.

Smart Growth  Well-planned development that protects open space and farmland, revitalizes communities, keeps housing affordable and provides more transportation choices.

Soft Costs  The design, legal, architectural, financing and other costs, plus fees, incurred when developing a real estate project. (As opposed to the "hard" construction costs.

Solar Collector  Any device used to capture or concentrate the sun's energy. The leaves on a tree can be considered a solar collector, as can a window, solar panel, or dark surfaced thermal mass.

Solar Orientation  See Orientation (solar).

Solar Panels  General term for an assembly of photovoltaic modules. See photovoltaic. Use of solar panels is a sustainable building strategy in that it lessens a building's reliance on nonrenewable sources of power distributed through the grid system.

Source Reduction  The design, manufacture, purchase or use of materials to reduce the amount or toxicity of waste in an effort to reduce pollution and conserve resources (i.e., reusing items, minimizing the use of products containing hazardous compounds, extending the useful life of a product and reducing unneeded packaging). Practices that reduce the amount of any hazardous substance, pollutant or contaminant entering any waste stream or otherwise being released into the environment. Such practices also reduce the risk to public health and the environment associated with such releases. Term includes equipment or technology modifications, substitution of raw materials, and improvements in housekeeping, maintenance, training or inventory control.

Special Districts  Geographic areas in which fees or taxes are collected to fund investments or services benefiting properties within the district.

Stack Effect  Air, as in a chimney, that moves upward because it is warmer than the ambient atmosphere.

Staging  The sequencing and physical positioning of building materials on a construction site. Sustainable building pays particular attention to staging in order to minimize the impact to the construction site and protect materials from damage.

Stakeholder  Any organization, governmental entity, or individual that has a stake in or may be impacted by a given approach to environmental regulation, pollution prevention, energy conservation, etc.

Streetscape  The space between the buildings on either side of a street that defines its character. The elements of a streetscape include: building frontage/façade; landscaping (trees, yards, bushes, plantings, etc.); sidewalks; street paving; street furniture (benches, kiosks, trash receptacles, fountains, etc.); signs; awnings; and street lighting.

Structural Insulated Panel (SIP)  Manufactured panels consisting of a sandwich of polystyrene between two layers of engineered wood paneling. Can be used for walls, roof, or flooring, and result in a structure very resistant to air infiltration.

Sustainability  Practices that would ensure the continued viability of a product or practice well into the future.

Sustainable Development  An approach to progress that meets the needs of the present without compromising the ability of future generations to meet their needs. Development with the goal of preserving environmental quality, natural resources and livability for present and future generations.

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Tankless water heater  See Demand Hot Water System.

Tax Increment Financing  A program designed to leverage private investment for economic development projects in a manner that enhances the benefits accrued to the public interest.

Thermal Break  Method of increasing the thermal performance of a material or assembly by reducing conductive heat loss. By inserting a less thermally conductive material in a material or assembly that bridges conditioned and unconditioned space, the conductive path is reduced or broken. An example is the thermal break featured in aluminum-framed windows.

Thermal Bridging  Unwanted heat loss or gain due to conduction through a material. An example of thermal bridging is heat loss that occurs with structural steel framing that is insufficiently insulated between conditioned and unconditioned space.

Thermal Mass  A mass (often stone, concrete, or brick) used to store heat and reduce temperature fluctuation in a space, by releasing heat slowly over time.

Tipping Fee  Charge for the unloading or dumping of waste at a recycling facility, composting facility, landfill, transfer station or waste-to-energy facility.

Total Volatile Organic Compounds  The total mass, typically in milligrams per cubic meter, of the organic compounds collected in air.

Toxic  Capable of having an adverse effect on an organism; poisonous; harmful or deadly.

Transfer of Development Rights  A system that assigns development rights to parcels of land and gives landowners the option of using those rights to develop or to sell their land. TDRs are used to promote conservation and protection of land by giving landowners the right to transfer the development rights of one parcel to another parcel. By selling development rights, a landowner gives up the right to develop his/her property, but the buyer could use the rights to develop another piece of land at a greater intensity than would otherwise be permitted.

Transit-Oriented Development (TOD)  The development of housing, commercial space, services, and job opportunities in close proximity to public transportation. Reduces dependency on cars and time spent in traffic, which protects the environment and can ease traffic congestion, as well as increasing opportunity by linking residents to jobs and services.

Tri-generation  The combined production of electricity, heat and cooling, and involves connecting cogeneration units with absorption cooling units (cooling produced from heat).

Trombe Wall  Thermal storage system used in passive solar design. A high-mass wall that stores heat from solar gain during the day and slowly radiates the heat back into the living space at night.

Truck Tire Wash Down Area  A strategy for removing dirt and other contaminants from construction vehicles in order to prevent stormwater contamination related to transport of contaminants offsite on vehicle tires. A specified area is created for wash down, with structural controls in place to prevent wash down waters from entering the storm system or the larger environment.

TXV (Also TEV) Thermostatic expansion valve  A TXV installed on an air conditioning system can dramatically improve the efficiency of the unit. When cooling demand is high, the valve opens up and lets more coolant pass through the indoor coils. When demand is low, the valve closes to reduce the refrigerant flow. AC units not equipped with TXVs have either a fixed orifice or capillary tube system.

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Urea-Formaldehyde Foam Insulation  A material once used to conserve energy by sealing crawl spaces, attics, etc.; no longer used because emissions were found to be a health hazard.

U (U-Value/U-factor)  A measure of the amount of heat that flows in or out of a substance under constant conditions when there is a one degree difference between the air within and outside a building. U-factor is used in determining the performance of a glazing system or window assembly and is always used as a summary measure for the conductive energy measure of building enclosures. The reciprocal of R-value.

Urban Forest  A forest or a collection of trees and shurbs that grow within a city, town or a suburb. In a wider sense it may include any kind of woody plant vegetation growing in and around human settlements. The benefits of urban forests are many, including beautification, reduction of the urban heat island effect, reduction of stormwater runoff, reduction of air pollution, reduction of energy costs through increased shade over buildings, enhancement of property values, improved wildlife habitat, and mitigation of overall urban environmental impact.

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Variance  The relaxation of requirements of a zoning district for a specific parcel or tract of land. Variances are often issued to avoid unnecessary hardships to a landowner.

Ventilation  Process by which outside air is conveyed to an indoor space.

Ventilation Control (by Occupants)  The ability of building occupants to control ventilation rates. A strategy for giving control of comfort back to occupants, this can be achieved through access to individual electronic controls or by operable windows in workspaces. Studies show that giving increased control to occupants over their environment results in greater occupant tolerance for variability in the indoor environment.

Ventilation Rate  The rate at which indoor air enters and leaves a building. Expressed as the number of changes of outdoor air per unit of time: air changes per hour (ACH), or the rate at which a volume of outdoor air enters in cubic feet per minute (CFM).

Visual DOE  See Energy Modeling

Volatile Organic Compound (VOC)  Organic substances capable of entering the gas phase from either a liquid or solid form. Building materials such as particle board, plywood, adhesives, paints, varnishes, carpet, drapes and furniture are often made with materials that off-gas VOCs, usually in the form of formaldehyde products. Other sources include some you may not think of: tobacco, burning gas, perfume, cleaning agents, hairspray and even copy and printing machines. Degrees of exposure to VOCs can cause everything from mild symptoms such as irritated eyes, ears and throat to more severe reactions such as wheezing and other respiratory problems. By using low-VOC products, exposures are reduced and indoor air quality is improved.

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Walk-off Mat  Design strategy for reducing the amount of contaminants introduced into an interior space by providing grating or other material to remove contaminants from shoes. A significant portion of contaminants in a building are brought in this way, impacting indoor environmental quality.

Waste Management Plan  See Construction Waste Management

Water-Source Heat Pump  Heat pump that uses wells or heat exchangers to transfer heat from water to the inside of a building. Most such units use ground water. (See groundsource heat pump; heat pump.) 1

Waterless Urinal  Urinal with no water line. Most designs use a specialized material that allows fluid to drain one-way into the sewer system.

Watts per Square Foot  A shorthand measure of the energy use of a building, often applied to indoor lighting. Energy codes often limit the watts per square foot based on building type and function.

Whole-house fan  Essentially a large fan that draws hot air out of a building and replaces it with cooler exterior air, as opposed to attic fans that only remove the hot air from the attic. Compared with an air conditioner, which can draw up to 6,000 watts, whole-house fans use about the same amount of electricity as a couple of light bulbs, or around 120 watts for smaller units up to about 700 watts for larger units. New homes of especially tight construction may need to have barometric vents installed a distance away from the exhaust intake to prevent negative pressure problems in the house, which could have an adverse effect on fuel-burning appliances. (Simply opening a couple of screened windows can also equalize the pressure.) It is important to prevent creating negative pressure around fuel-burning appliances in the house and starving them for combustion air as the fire can actually leave the firebox looking for oxygen. A good whole-house fan can reduce the interior temperature of a house by 10 to 15 degrees within about 20 minutes, as well as create a "sensible" feeling that the moving air is cooler. The exhaust intake is usually located in the highly heated attic air space, and many homes use a gravity damper system in the ceiling that opens automatically as the systems operates and then seals closed upon shut-down.

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Zero-lot-line Development  A development option where side yard restrictions are reduced and the building abuts a side lot line. Overall unit-lot densities are therefore increased. Zero-lot-line development can result in increased protection of natural resources.

Zoning  Classification of land in a community into different areas and districts. Zoning is a legislative process that regulates building dimensions, density, design, placement and use within each district.

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