Glossary for building green home items
Active closed-loop solar water heater: Solar water heater in which an electric pump circulates a freeze-protected heat-transfer fluid through the collector and heat exchanger within a storage tank.
Active drainback solar water heater: Solar water heater in which water or another heat-transfer fluid is pumped through the collector and drains back to a tank in the house when the pump turns off.
Advanced framing: House-framing technique in which lumber use is optimized, improving both the material efficiency of the house and the energy performance of the building envelope.
Air barrier: Layer in the building envelope that effectively blocks air movement, which also blocks the flow of most water vapor.
Air handler: Fan that a furnace, whole-house (central) air conditioner, or heat pump uses to distribute heated or cooled air throughout the house.
Air-source heat pump: Heat pump that relies on the outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps.
Airtight drywall: Use of drywall with carefully sealed edges and joints to serve as the air barrier in a wall or ceiling system.
Annual Fuel Utilization Efficiency (AFUE): Energy efficiency of a heating system that accounts for start-up, cool-down, and other operating losses that occur during real-life operation; AFUE is always lower than combustion efficiency.
Autoclaved aerated concrete (AAC): Masonry building material used throughout much of the world for more than 70 years; made of portland cement, sand, and water; an autoclaving process (heating under pressure) during the setting results in the production of air pockets in the material, making it less dense and better insulating.
Backdrafting: Indoor air quality problem in which potentially dangerous combustion gasses escape into the house instead of going up the chimney.
Balanced ventilation: Mechanical ventilation system in which separate, balanced fans exhaust stale indoor air and bring in fresh outdoor air; often includes heat recovery or heat and moisture recovery (see also heat-recovery ventilator and energy-recovery ventilator).
Batch solar water heater: See integral collector storage (ICS) solar water heater.
Binder: Glue used in manufacturing wood products, such as medium-density fiberboard (MDF), particleboard, and engineered lumber. Most binders are made with formaldehyde. See urea-formaldehyde binder and methyl diisocyanate (MDI) binder.
Bioaccumulate: Process by which toxins can build up in the food chain; small organisms often store toxins in their fatty tissues, and when larger organisms eat them, those toxins become more concentrated. At the top of the food chain (polar bears and humans, for example), the levels of toxins can become very high.
Blowing agent: Compound used in producing foam insulation; mixed as a liquid with the foam ingredients under pressure, the blowing agent evaporates, creating gas bubbles that provide the insulation. Until recently, most blowing agents (HCFCs and CFCs) depleted the Earth’s protective ozone layer; except for extruded polystyrene, industry has now switched to ozone-safe blowing agents.
Boiler: System used to heat water for hydronic heating. Most boilers are gas-fired or oil-fired, although some are electric or wood-fired; a boiler can also heat water through a tankless coil or an indirect water heater.
Borate: Chemical containing the element boron that provides fire resistance to materials such as cellulose insulation and decay resistance to wood products.
Brominated flame retardant (BFR): Chemicals added to various plastics and foam materials to provide fire resistance; there is growing concern that BFRs are harmful to humans.
Brownfield: Land that has been contaminated from past (usually industrial) uses.
Btu: British thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature; about the heat content of one wooden kitchen match.
Building envelope: Exterior layer of a house that provides protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation.
Capillary forces: Forces that lift water or pull it through porous materials, such as concrete.
Carbon-neutral: House that, on an annual basis, does not result in a net release of carbon dioxide (a greenhouse gas that contributes to global warming) into the atmosphere.
Catalytic combuster: Specialized component in a combustion device, such as a wood stove, that results in more complete combustion, thus improving efficiency and reducing pollution.
Cathodic protection rod: Metal rod in a storage-type water heater that protects the tank from corrosion; the sacrificial cathodic protection rod is eaten away over time and can be replaced.
Cavity-fill insulation: Insulation installed in the space created by wall, ceiling, roof, or floor framing; most commonly fiberglass-batt, spray-applied or dense-pack cellulose, or spray polyurethane.
Chromated copper arsenate (CCA): Type of wood preservative that has now been eliminated from most wood products due to concerns about leaching and toxicity; huge quantities of CCA-treated wood remain in use, especially in residential decks.
Cistern: Vessel for storing water, such as that collected with a rainwater harvesting system.
Clerestory windows: Vertical, or close-tovertical, windows in a flat-roof house that bring sunlight deeply into the building.
Cohousing: Development pattern in which multiple (typically 8 to 30) privately owned houses or housing units are clustered together with some commonly owned spaces, such as common house, workshop, greenhouse, etc.; automobiles are typically kept to the outside perimeter of the community, resulting in a protected area where children can play.
Combustion air: Air used for burning fuel in heating and water-heating systems; outdoor air may be delivered directly to the combustion chamber in a sealed-combustion system.
Combustion chamber: Portion of a furnace, boiler, or other combustion appliance where fuel is burned to produce useful heat.
Combustion efficiency: Efficiency at which a fuel is burned in a combustion appliance when operating at its rated output; the combustion efficiency is always higher than the annual fuel utilization efficiency (AFUE).
Compact fluorescent lamp (CFL): Fluorescent light bulb in which the tube is folded or twisted into a spiral to concentrate the light output; CFLs are typically 3 to 4 times as efficient as incandescent light bulbs, and they last 8 to 10 times as long.
Composting system: Outdoor bin or group of bins for converting vegetable scraps, weeds from the garden, and other plant matter into a rich, high-organic-content soil amendment.
Composting toilet: Toilet that does not flush human waste down the drain using potable water; instead, the wastes are stored in a composting chamber that decomposes the waste. Most of the waste is converted into water vapor and carbon dioxide and vented into the outside air; a small amount of rich, organic humus is removed annually and can be spread around non-food plants.
Concrete masonry unit (CMU): Block made of concrete used for wall construction; hollow cores can be filled with concrete to reinforce walls.
Conduction: Movement of heat through a material as kinetic energy is transferred from molecule to molecule; the handle of an iron skillet on the stove gets hot due to heat conduction. R-value is a measure of resistance to conductive heat flow.
Constructed wetland: Specialized artificial wetland that relies on microorganisms living around plant roots to purify wastewater.
Convection: Movement of heat from one place to another by physically transferring heated fluid molecules, usually air or water. Natural convection is the movement of that heat naturally; forced convection relies on fans or pumps.
Cost-plus basis: System of payment for services in which a builder charges an hourly rate for construction labor, the direct cost of materials, and a pre-established profit level.
Cripple studs: Studs in a wall system that support headers above windows or doors; these additional studs result in extra heat loss because they do not insulate as well as the insulation in the wall cavity.
Cross-linked polyethylene (PEX): Specialized type of polyethylene plastic that is strengthened by cross-linking (chemical bonds formed in addition to the usual bonds in the polymerization process). PEX is used primarily as tubing for hot-and cold-water distribution and radiant-floor heating.
Current loop: In electrical wiring, a situation in which separation of hot and neutral leads results in higher-than-normal electromagnetic fields (EMF).
Curtain truss: Known also as a Larson truss, a non-structural truss that extends out from a structural wall system for the purpose of holding cavity-fill insulation. Often used on timber-frame houses, curtain trusses may be as much as 12 inches deep, providing an insulating value greater than R-40. Since they aren’t structural, curtain trusses are often constructed from 2x2s with plywood reinforcement flanges to minimize wood use.
Daylighting: The use of sunlight for daytime lighting needs.
Deep-cycle battery: Specialized battery for storing electricity that can be deeply discharged and recharged many times; used for homes with stand-alone power systems (non-grid-connected) that rely on photovoltaic or wind power.
Degree day: Measure of heating or cooling requirements based on the average outdoor temperature. To calculate the number of heating degree days for a given day, find the average of 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, which measure air conditioning requirements, are calculated much the same way, but based on the difference between the average outdoor temperature and an indoor base temperature, usually 75°F.
Demand water heater: Water heater that heats water only as needed; there is no storage tank and, thus, no standby heat loss. While electric demand water heaters may make sense for a remote sink in a house, demand water heaters fired by natural gas or propane are gen‑
erally more practical for whole-house use, given the hot water loads of showering and clothes washing.
Design temperature: Reasonably expected minimum (or maximum) temperature for a particular area; used in sizing heating and cooling equipment.
Design-build firm: Company that handles both house design and construction; since both services are provided by the same firm, integrated design can easily be achieved.
Diffuser: With forced-warm-air heating system, a register or grille attached to ducting through which heated or air conditioned air is delivered to the living space; with tubular skylight and electric light fixture, a cover plate through which diffused light is delivered.
Direct-gain system: Type of passive solar heating system in which south-facing windows provide heat gain during the daytime and high-mass thermal-storage materials absorb and store that heat to keep the space warm at night. This is the simplest type of passive solar heating system, but careful design is required to prevent overheating.
Double wall: Construction system in which two layers of studs are used to provide a thicker-than-normal wall system so that a lot of insulation can be installed; the two walls are often separated by several inches to reduce thermal bridging through the studs and to provide additional space for insulation.
Drywall clips: Simple metal or plastic clips that are used to tie sheets of drywall together, especially at inside corners; use of a few clips can eliminate one or two wall studs, thus leaving more room for insulation. Because such a corner can float, cracking of the drywall joint is less common.
Dual-flush toilet: Toilet that provides two flush levels: a full-volume flush for use with solid wastes, and a reduced-volume flush (often half the volume) when only liquid waste and paper need to be flushed.
Dutch drain: Open drain at the bottom of a house wall to carry stormwater (rainwater runoff) away from the house.
Earth-bermed: Earth built up around the walls of a house to reduce heat loss, protect against wind, and reduce noise; superb moisture management and drainage are critically important with earth-bermed and underground houses.
Ecological footprint: Measure of the amount of land and water required to support a person or population of people; includes both resource extraction and waste disposal.
Effective R-value: See mass-enhanced R-value.
Electric-resistance heat: Heat provided by electricity in which high-resistance wires convert electric current directly into heat. See also heat pump.
Electromagnetic field (EMF): Field given off by electric current flow. Some health experts are concerned that the magnetic field component of EMFs may be harmful or even cancer-causing. Magnetic fields are stronger near current in which there is separation between the positive and neutral leads.
Electronically commutated motor (ECM): Specialized, energy-efficient electric motor whose output can be reduced to save energy; most commonly used with fans and pumps.
Embodied energy: Energy that goes into making a product; typically includes energy for transporting both the raw materials and the finished product.
Endocrine disruptor: Chemical that mimics natural hormones, such as estrogen, and may interfere with reproductive development or alter behavior in offspring. Includes such commonly used chemicals as phthalate plasticizers used in PVC plastic and bisphenol-A used in epoxies and polycarbonate plastic.
Energy efficiency rating (EER): As most commonly used, EER is the operating efficiency of a room air conditioner, measured in Btus of cooling output, divided by the power consumption in watt-hours; the higher the number the greater the efficiency.
Energy factor: Efficiency measure for rating the energy performance of dishwashers, clothes washers, water heaters, and certain other appliances; the higher the number the greater the efficiency.
Energy-efficient mortgage (EEM): Special type of mortgage in which the lending institution raises the allowable mortgage amount for a given earnings level, since energy-saving features in the house will reduce the monthly operating costs, thus leaving more money available to pay the mortgage.
EnergyGuide: Label from the Federal Trade Commission that lists the expected energy consumption of an appliance, heating system, or cooling system, and how that consumption compares with other products in that category; the energy performance is based on specified operating conditions and average energy costs — your actual performance may vary.
Energy-recovery ventilator (ERV): Type of heat-recovery ventilator (HRV) that captures water vapor as well as heat from the outgoing airstream in a balanced ventilation system. In winter months, this can reduce the drying that occurs when outdoor air is brought indoors and warmed.
ENERGY STAR: Labeling system sponsored by the US Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners.
Engineered header: A framing member made of engineered lumber, used to carry a wall or roof load above a window or door.
Engineered lumber: Lumber made by gluing together veneers or strands of wood to create very strong framing members; stronger and less prone to warping than standard framing lumber and can be made from smaller-diameter trees.
Environmental footprint: Measure of one’s overall burdens or impacts on the environment. See also ecological footprint.
Evaporative cooler: Energy-efficient cooling system in which a fine mist of water is evaporated, lowering the air temperature; most appropriate in dry climates, as they add humidity to a house. Also known as a swamp cooler.
Exhaust-only ventilation: Mechanical ventilation system in which one or more fans are used to exhaust air from a house, with make-up air supplied passively. See also balanced ventilation.
Expanded polystyrene (EPS): Type of rigid foam insulation; unlike extruded polystyrene (XPS), EPS does not contain ozone-depleting HCFCs.
Extruded polystyrene (XPS): Type of rigid foam insulation that is widely used below-grade, such as underneath concrete floor slabs; in North America XPS is currently made with ozone-depleting HCFC-142b.
Fan-coil: Electric or hydronic heating or cooling element installed in a duct; lets ventilation air also warm or cool the living space.
Ferrocement: Mix of portland cement, sand, and water that is sprayed on a steel mesh, creating a thin, strong material; often used for cisterns.
Fiber-cement siding: Siding material made from wood fiber and portland cement that is highly durable, moisture-resistant,
and fire-proof; developed in New Zealand, is becoming common as a siding material in North America.
First cost: Initial cost of buying or building something, as distinguished from the operating cost.
Flashing: Material, usually sheet metal, rubber, or plastic, installed to keep rain from entering a building; when properly installed in a wall or roof assembly, flashing sheds rain to the exterior.
Fluorescent lighting: Type of energy-efficient lighting introduced in the 1930s in which electric discharge within a sealed glass tube energizes mercury vapor, producing ultraviolet (UV) light; this UV light is absorbed by a phosphor coating on the inside surface of the glass tube, which in turn fluoresces, generating visible light. See also compact fluorescent lamp.
Fluoropolymer: Polymer (compound made up of many identical molecules linked by chemical bonds) containing the element fluorine; the most recognized fluoropolymer is DuPont’s Teflon®, or polytetrafluoroethylene (PTFE). A key constituent in making fluoropolymers, perfluorooctanoic acid (PFOA), has come under fire as a “likely carcinogen.”
Forced-air heating: Heat distribution system in which heat is delivered by forcing warm air through a network of ducts. A furnace or heat pump typically generates the warm air.
Formaldehyde: Chemical found in many building products; most binders used for manufactured wood products are formaldehyde compounds. Reclassified in 2004 as a “known human carcinogen.” See also phenol-formaldehyde binder and urea-formaldehyde binder.
Fuel cell: Electrochemical device similar to a battery in which electricity is generated by chemically reacting hydrogen with oxygen; electricity, water vapor, and heat are the only products.
Furnace: System used to heat air for a forced-air heating system. Furnaces can be gas-fired, oil-fired, wood-fired, or electric.
Galvanized coating: Protective zinc coating added to steel to reduce corrosion.
Glazing: When referring to windows or doors, the transparent or translucent layer that transmits light; high-performance glazings may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill.
Gravity-flush toilet: Toilet whose flush is powered solely by the force of falling water. See also pressure-assist toilet.
Graywater: Wastewater from a building that does not include flush-water from toilets and (as most commonly defined) water from kitchen sinks or dishwashers.
Green building: Design and construction of buildings that minimize impacts on the environment while helping to keep occupants healthy.
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: Mortgage that acknowledges a green home’s lower monthly operating costs due to reduced energy use or reduced need for automobiles. Because of these lower monthly operating costs, the amount of allowable mortgage is increased.
Green power: See green electricity.
Greenfield: Site that has not previously had a building on it. See also brownfield.
Grid-connected power system: Electricity generation system, usually relying on photovoltaics or wind power, that is hooked up to the utility company’s electric grid through a net-metering arrangement so that electricity can be obtained when the locally generated power is not sufficient. See also standalone power system.
Ground-source heat pump: Heat pump that relies on the relatively constant temperatures underground as the heat source and heat sink. The energy performance of ground-source heat pumps is usually better than that of air-source heat pumps.
Gut-rehab: Building renovation in which the walls are gutted (reduced to the wall framing and sometimes sheathing).
Hard-coat (pyrolytic) low-e: Type of low-e coating in which a heat-reflective metal coating is formed into the surface of the glass during manufacturing (pyrolytic refers to heat), rather than being applied after the glass is made — as is the case with soft-coat low-e coatings.
Heat distribution: System for delivering heat throughout a house. See forced-air heating and hydronic heating.
Heat exchanger: Device that allows for transfer of heat from one material to another. An air-to-air heat exchanger, or heat-recovery ventilator, transfers heat from an outgoing airstream to an incoming airstream. A copper-pipe heat exchanger in a solar water heater tank transfers heat from the heat-transfer fluid circulating through a solar collector into 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.
Heating Season Performance Factor (HSPF): Energy performance of an air-source heat pump operating in heating mode; it is the ratio of the estimated seasonal heat output divided by the seasonal power consumption. See also seasonal energy efficiency ratio (SEER).
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. See also energy-recovery ventilator.
Heat sink: Where heat is dumped by an air conditioner or heat pump used in cooling mode; usually into the outdoor air or ground. See air-source heat pump and ground-source heat pump.
High-efficiency toilet (HET): Toilet that provides at least 20% water savings over the federal standard of 1.6 gallons per flush and still meets rigorous standards for flush performance.
Home-run plumbing system: Water-distribution piping system in which individual plumbing lines extend from a central manifold to each plumbing fixture or water-using appliance; piping is typically cross-linked polyethylene (PEX). Because diameter of the tubing can be matched to the flow of the fixture or appliance, hot water can be delivered more quickly.
Horizontal-axis clothes washer: Washing machine (typically front-loading) in which the laundry drum is configured horizontally; this allows significant water savings, because the laundry is dipped into and out of the wash water as the drum rotates. See also vertical-axis clothes washer.
Hydrochlorofluorocarbon (HCFC): Compound commonly used as a refrigerant in compression-cycle mechanical equipment (refrigerators, air conditioners, and heat pumps) or as a blowing agent in producing foam insulation. HCFCs are damaging to the Earth’s protective ozone layer.
Hydronic heating: Heat distribution system in which hot water produced by a boiler is circulated through pipes and baseboard
radiators or tubing in a radiant floor. Also called baseboard hot-water heating.
Hydropower: Generation of electricity from falling or flowing water.
Impervious surface: Surface that does not permit stormwater runoff to infiltrate the ground. See also porous paving.
Incandescent light: Light produced by a standard light bulb when electric current heats a tiny coiled filament to glowing; converts about 90% of the electricity into heat and only 10% into light. See also fluorescent lighting.
Indirect water heater: Water heater that draws heat from a boiler used for space heating; a separate zone from the boiler heats water in a separate, insulated tank via a water-to-water heat exchanger. See also tankless coil.
Indoor air quality (IAQ): 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.
Infill site: Building site sandwiched between existing buildings in a fairly developed area; by developing infill sites, there is less pressure on greenfield sites and residents often have better access to public transportation.
Instantaneous water heater: See demand water heater.
Insulated concrete form (ICF): Hollow insulated forms, usually made from expand- ed polystyrene (EPS), used for building walls (foundation and aboveground); after stacking and stabilizing the forms, the aligned cores are filled with concrete, which provides the wall structure.
Integral collector storage (ICS) solar water heater: A simple solar water heater in which potable water is heated where it is stored.
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 can be created cost-effectively using integrated design, since higher costs in one place can often be paid for through savings elsewhere — e.g. by improving the performance of the building envelope, the heating and cooling systems can be downsized, or even eliminated.
Inverter: Device for converting direct-current (DC) electricity into the alternating-current (AC) form required for most home uses — necessary if home-generated electricity is to be fed into the electric grid through net metering arrangements.
Kilowatt-hour (kWh): A measure of electricity consumption; a 100-watt light bulb burning for 10 hours consumes 1 kWh.
Leach field: An area of permeable soil into which effluent from a septic tank is able to infiltrate the ground; a component of an on-site wastewater disposal system.
Leaching: Relative to materials, this is the process by which chemicals can escape in the environment; for example, arsenic can leach out of older pressure-treated wood.
Life cycle: Entire life of a product or material, from raw material acquisition through disposal.
Life-cycle assessment (LCA): Examination of environmental and health impacts of a product or material over its life cycle; provides a mechanism for comparing different products and materials for green building.
Life-cycle cost: Economic cost of a product or building over its expected life, including both first cost (purchase cost) and operating cost.
Living Machine: Ecological wastewater treatment system that relies on biological systems (microorganisms, plants, and animals) to purify wastewater, usually used for municipal-scale treatment systems.
Low-conductivity gas fill: Transparent gas installed between two or more panes of glass in a sealed, insulated window that resists the conduction of heat more effectively than air; boosts a window’s R-value and reduces its U-factor.
Low-e coating: Very thin metallic coating on glass or plastic window glazing that reduces heat loss through the window; the coating emits less radiant energy (heat radiation), which makes it, in effect, reflective to that heat; boosts a window’s R-value and reduces its U-factor.
Make-up air: Outside air supplied to replace household air that was used in a combustion appliance or exhausted through a ventilation system.
Manifold: With a home-run plumbing system, the manifold is the component that distributes the water; it has one inlet and many outlets to feed different fixtures and appliances.
Masonry heater: Specialized, high-mass, wood-burning fireplace in which a small fire is burned very efficiently at very high temperature; the fire heats up the thermal mass of the masonry heater, which then radiates heat to the living space. In a well-insulated home, it often only has to be burned once or twice per day.
Mass-enhanced R-value: The higher R-value performance of a high-mass wall material; it takes into account the fact that such a material absorbs and stores heat during the daytime and, thus, results in lower overall heat loss. Mass-enhanced R-values are climate-specific; in sunny climates with high daily temperature swings, such as Rocky Mountain states, the boost will be more significant. Also called effective R-value, and commonly exaggerated by manufacturers of masonry building systems.
Materials recovery facility (MRF): Solid waste processing facility, often operated by a municipality, in which waste materials are separated for recycling or separate disposal streams.
Mechanical ventilation: Ventilation system using a fan or several fans to exhaust stale indoor air from a home as away to ensure adequate indoor air quality. See exhaust-only ventilation and balanced ventilation.
Medium-density fiberboard (MDF): Panel product used in cabinets and furniture; generally made from wood fiber glued together with binder; similar to particleboard, but with finer texture, offering more precise finishing. Most MDF is made with formaldehyde-emitting urea-formaldehyde binders.
Methyl diisocyanate (MDI) binder: Non-formaldehyde binder used in some medium-density fiberboard and particleboard products, including straw-based particleboard.
Mixed-use development: Development pattern in which such building types as residential, retail, and commercial office are located in the same area; beneficial because it can reduce dependence on automobiles.
Mulch: Organic material, such as leaves, straw, or chipped wood waste, spread on the ground and around plantings to reduce the need for irrigation and weeding.
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. The utility effectively buys the power at the retail price, but the amount of electricity the utility company will “buy” in a given month is limited to the amount that the homeowner buys; any excess electricity is purchased at a much lower, wholesale price. See grid-connected power system.
Offgassing: Release of volatile chemicals from a material or product. See also volatile organic compounds.
On-center: As used in house construction, the distance from the center of one framing member to the center of another; in wood-frame construction, studs are typically 16 or 24 inches on-center.
On-demand hot water circulation: System to quickly deliver hot water to a bathroom or kitchen when needed, without wasting the water that has been sitting in the hot-water pipes, which circulates back to the water heater.
On-site wastewater system: Treatment and disposal of wastewater (sewage) from a house that is not connected to a municipal sewer system; most on-site systems include a septic tank and leach field.
Operating cost: Cost of operating a device or building; includes energy, maintenance, repairs, etc.
Operating energy: Energy required to operate something, such as a house.
Oriented strand board (OSB): Wood sheathing or subfloor panel made from strands of wood glued together in layers oriented for strength; most OSB is made using phenol-formaldehyde binder or methyl diisocyanate (MDI) binder.
Owner-builder: Homeowner who builds his or her own home.
Particleboard: Panel product used in cabinets and furniture; generally made from wood fiber glued together with binder. Similar to medium-density fiberboard (MDF), but with a coarser texture. Most particleboard is made with formaldehyde-emitting urea-formaldehyde binder, although some wood particleboard and all straw particleboard uses a non-formaldehyde methyl diisocyanate (MDI) binder.
Passive solar heating: Building design in which solar energy provides a significant portion of the heating without the use of fans or pumps; the building itself serves as the solar collector and heat storage system. See also direct-gain system and thermal storage wall.
Payback period: Length of time it takes to pay back the cost of the investment. For example, water and energy savings from replacing an old showerhead with a new, water-saving model can often pay back the investment in a few months; the payback period for a photovoltaic power system will be much longer.
Peak watt: Unit of rated power output, for example from a photovoltaic (PV) module in full sunlight, as distinct from its output at any given moment, which may be lower.
Pellet stove: Wood stove designed to burn pellets made from compressed sawdust; screw-auger feeds pellets into the firebox at a metered rate; electric fan provides combustion air.
Permaculture: Term coined by Bill Mollison for the practice of designing sustainable human habitats; intended to mean both “permanent agriculture” and “permanent culture.”
Phenol-formaldehyde binder: Formaldehyde-based binder used for wood products, especially those made for exterior applications; lower formaldehyde emissions than urea-formaldehyde binder.
Phosphate: Nutrient contained in some detergents that results in excessive vegetative growth in water bodies.
Photovoltaic (PV) cell: Device that generates electricity from sunlight; multiple PV cells are combined into a PV module.
Photovoltaics (PV): Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. See also PV module and PV array.
Phthalate plasticizer: Chemical added to polyvinyl chloride (PVC) and some other plastics to make them more flexible; phthalates are endocrine disruptors.
Pier foundation: Building foundation consisting of piers instead of continuous walls; resource-efficient because it avoids the need for continuous foundation walls.
Plasticizer: Chemical compound added to a material to make it more flexible or softer. See phthalate plasticizer.
Platform framing: The most common house framing system in North America; a platform, or deck, is constructed at each floor level, and on top of this the house walls are erected.
Polychlorinated biphenyl (PCB): Highly toxic chemical that was long used as a fire-resistant coolant in electrical ballasts and other products; PCBs were banned in the 1970s, but remain a very significant problem today.
Polyisocyanurate (polyiso): Type of rigid foam insulation used in above-grade walls and roofs; typically has a foil facing on both sides; was made with ozone-depleting HCFC-141b blowing agent, but manufacturers have switched to ozone-safe hydrocarbons.
Polyurethane foam: Insulation material made from polyol and isocyanate and a blowing agent that causes it to expand; typically sprayed into wall cavities or sprayed on roofs.
Polyvinyl chloride (PVC): Most common plastic in building construction; widely used in such applications as drainage piping, flooring, exterior siding, window construction, and electrical wire. Also known as vinyl.
Porous grid paver: Concrete or stone porous paving material designed to allow stormwater to infiltrate the ground.
Porous paving: A paving material that allows rainfall to percolate through and infiltrate the ground, rather than contributing to stormwater runoff; can be asphalt, concrete, or porous grid paver.
Portland cement: The most common building material in the world; a fine gray powder made from limestone, gypsum, and shale or clay; when mixed with water, cement binds sand and gravel into concrete. Portland cement was invented in 1824 by Joseph Aspdin, a British stone mason, who named it after a natural stone quarried on the Isle of Portland off the British coast.
Post-and-beam construction: Construction system using a relatively small number of structural timber, steel, or concrete framing members, with non-structural infill walls or insulated panels. See also timber framing.
Post-consumer recycled material: Material recovered from a waste product that has been in use by a consumer before being discarded. See also post-industrial recycled material.
Post-industrial (pre-consumer) recycled material: Material recovered from the waste stream of an industrial process that has not been placed in use. See also post-consumer recycled material.
Potable water: Water considered safe for drinking and cooking.
Pressure-assist toilet: Toilet that uses air pressure, generated as the toilet tank refills, to produce a more forceful flush; some of the highest-performance, high-efficiency toilets (HETs) rely on pressure-assist technology.
Pressure-treated wood: Wood that has been chemically treated to extend its life, especially when outdoors or in ground contact. The most common pressure-treated wood until a few years ago, chromated copper arsenate (CCA), has now been phased out for most applications, due to health and environmental concerns.
Prudent avoidance: Strategy using relatively easy and low-cost tactics to avoid exposure to something that may prove to be harmful, such as electromagnetic fields (EMFs).
PV array: Group of PV modules wired together to increase total power output.
PV module: Panel made up of photovoltaic cells; generates electricity directly from sunlight.
R-value: Measure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor.
Radiant energy: Energy transmitted by electromagnetic waves.
Radiant-floor heating: Heat distribution system in which a floor serves as a low-temperature radiator. When used with hydronic heating, hot water is usually circulated through tubing embedded in a concrete slab; alternately, the tubing can be installed on the underside of wood subflooring, although the benefit of thermal mass is lost.
Radiation: Movement of energy via electromagnetic waves.
Radon: Colorless, odorless, short-lived radioactive gas that can seep into homes and result in lung cancer risk. Radon and its decay products emit cancer-causing alpha, beta, and gamma particles.
Rainscreen: Construction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch.
Recirculating sand filter: Treatment system in which wastewater is circulated through a bed of sand or specialized media, where both aerobic and anaerobic conditions support bacteria that break down organic matter and convert nitrates into atmospheric nitrogen.
Reflective roofing: Roofing material that reflects most of the sunlight striking it to help reduce cooling loads; the ENERGY STAR Cool Roof program certifies roofing materials that meet specified standards for reflectivity.
Refrigerant: Compound used in refrigerators, air conditioners, and heat pumps to transfer heat from one place to another, thus cooling or heating a space. Most refrigerants today are hydrochlorofluorocarbons (HCFCs), which deplete the ozone layer.
Renewable Energy: Energy produced using solar, wind, hydropower, or biomass energy sources; can be thermal or electric energy.
Room air conditioner: Air conditioner installed in a window or through a wall; usually used to cool a relatively small area — although with a very energy-efficient, tight house, a single room air conditioner may be able to cool the entire space. See also whole-house (central) air conditioner.
Salt-box: Style of house, commonly built in Colonial New England, in which most of the windows are on the taller south-facing wall, and the roof slopes down to a relatively short north wall to help deflect wind.
Sealed combustion: Combustion system for space heating or water heating in which outside combustion air is fed directly into the combustion chamber and flue gasses are exhausted directly outside.
Seasonal energy efficiency ratio (SEER): Energy performance rating of a whole-house (central) air conditioner or heat pump operating in the cooling mode; it is the ratio of the estimated seasonal cooling output divided by the seasonal power consumption in an average climate.
Semiconductor: Material, such as silicon, whose electrical properties can be altered to make it either electrically conductive or insulating; used in electronic
devices such as computer chips and in photovoltaics.
Septic tank: Tank into which raw wastewater (sewage) from a house with an on-site wastewater disposal system flows. Anaerobic (oxygen-deprived) bacteria in the tank destroy pathogens in the wastewater and decompose the organic waste; effluent from the tank flows through pipes and drains into the ground in a leach field.
Sheathing: Material, usually plywood or oriented strand board (OSB), installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on sheathing.
Soft-coat low-e: Very thin metallic coating that is sputtered onto glass to improve its performance in reducing heat loss; because they are delicate, soft-coat low-e coatings must be protected within sealed insulated-glass units. See also hard-coat (pyrolytic) low-e.
Soil amendment: Material added to soil to make it more fertile or improve its moisture-holding capacity; chopped, recycled drywall can be used as such.
Solar AquaticTM system: See Living Machine. Solar collector: Device for capturing solar
energy and transferring heat to water or
air that circulates through.
Solar gain: Sunlight entering a building; for example, a passive solar direct-gain system.
Solar heat gain coefficient (SHGC): The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.
Spec house: House built on speculation in other words without a buyer already identified.
Spline: With structural insulated panel (SIP) construction, refers to connectors used to join panels; plywood splines are often installed in routed grooves in the foam insulation next to the interior and exterior oriented strand board (OSB) skins.
Stand-alone power system: Self-contained electricity generation and storage system, usually powered by photovoltaics or wind power, that is not connected to the electric grid. See also grid-connected power system.
Stormwater: Runoff from rain that is either carried offsite in storm sewers or allowed to infiltrate the ground; storm-water can be reduced through the use of porous paving and other infiltration strategies.
Straw: Stems left after harvesting cereal grains. Baled straw is used for strawbale construction; chopped straw can be manufactured into particleboard.
Strawbale construction: Construction system in which walls are built out of stacked baled straw and plastered on the interior and exterior surfaces. strawbale walls can be load-bearing (carrying the roof load) or non-load-bearing (in which a post-and-beam structural frame carries the roof load).
Stress-skin panel: Non-structural, insulated panels used for enclosing and insulating a timber-frame house; the interior skin is typically drywall and the exterior skin is oriented strand board (OSB).
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.
Sump: Reservoir or pit in the basement of a house into which water can drain, especially during flooding; a sump pump is used to pump collected water out of this reservoir.
Sunspace: Passive solar extension on the south side of a house used as a sunny daytime living space and as a heat source for the house; a key design feature is the ability to close the connections between the sunspace and house (typically windows and doors) at night. Can also be used for growing plants.
Suntempering: Practice of using a modest area of south-facing windows to provide limited passive solar heating to a house.
Superinsulate: To insulate extremely well; a house with very efficient windows and tight construction results in very low heating and cooling costs.
Swale: Low area of ground used for drainage and, often, the infiltration of stormwater.
Swamp cooler: See evaporative cooler.
Tankless coil: Heat exchanger integrated into a boiler used for heating water. Effective in the winter months when the boiler is operating for space heating, but tankless coils waste energy in warmer months, since they require the boiler to fire up every time hot water is drawn.
Therm: Unit of heat equal to 100,000 British thermal units (Btus); commonly used for natural gas.
Thermal bridging: Heat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel.
Thermal 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.
Thermal storage wall: Type of passive solar heating system in which sunlight shines through south-facing glass or plastic glazing and is absorbed by the outer surface of a high-mass wall; the wall surface heats up and that heat is stored in and conducts through the wall to warm the living space. Also called a Trombe wall.
Thermosiphon solar water heater: Solar water heater that operates passively (through natural convection) to circulate water through a solar collector and into an insulated storage tank situated above the collector; pumps and controls are not required.
Timber frame: Type of post-and-beam construction relying on large structural timbers.
Top plate: In wood-frame construction, the framing member that forms the top of a wall. In advanced framing, a single top plate is often used in place of the more typical double top plate.
Track-off mat: Mat at a house entrance across which people scuff their feet to remove moisture, dirt, and other particulates; important for keeping contaminants out and reducing cleaning requirements.
Trombe wall: Pronounced “Trome.” See thermal storage wall.
Tubular skylight: Round skylight that transmits sunlight down through a tube with internally reflective walls, even through an attic space; it delivers day-lighting through a ceiling light diffuser. Most tubular skylights are 12 to 16 inches in diameter and deliver light comparable to several 100-watt incandescent light bulbs.
U-factor: Measure of the heat conducted through a given product or material the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2 °Fhr). U-factor is the inverse of R-value.
Universal design: Design that makes a building accessible to as many individuals as possible, including older people and those with physical handicaps.
Unvented (or vent-free) gas heater: Gas-burning space heater that is not vented to the outdoors. While unvented gas heaters burn very efficiently, indoor air quality experts strongly recommend against their use because combustion gasses, including high levels of water vapor, are released into the house.
Urea-formaldehyde binder: Interior-grade formaldehyde-based binder used for particleboard, medium-density fiberboard (MDF), and hardwood plywood; higher formaldehyde emissions than phenol-formaldehyde binder.
UV light treatment: Water treatment system in which water passes through a column where it is exposed to ultraviolet light to kill any pathogens.
Vapor diffusion: Movement of water vapor through a material; water vapor can diffuse through even solid materials if the permeability is high enough.
Vapor retarder: Layer that inhibits vapor diffusion through a building envelope; examples include polyethylene sheeting, foil facing, and low-permeability paints.
Ventilation: Replacement of stale indoor air with fresh outdoor air — usually with fans, but sometimes naturally through building design elements. See also heat recovery ventilator.
Venturi effect: Increase in fluid velocity as flow is constricted; also, the principle by which air is drawn into a stream of water to increase the force of the flow. Used to enhance performance of some low-flow showerheads.
Vernacular: The architectural style that is specific to a certain region and that typically evolved in response to local climatic conditions.
Vertical-axis clothes washer: Top-loading washing machine with a tub that rotates back and forth and spins on a vertical axis, i.e., the center of rotation is a line extending up from the center of the tub. See also horizontal-axis clothes washer.
Vinyl: Common term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate).
Volatile organic compound (VOC): An organic compound that evaporates readily into the atmosphere; as defined by the US Environmental Protection Agency, VOCs are organic compounds that volatize and then become involved in photochemical smog production.
Waste management plan: Plan that addresses the collection and disposal of waste generated during construction, usually including the collection and storage of recyclable materials.
Wastewater: Used water from toilets, showers, sinks, dishwashers, clothes washers, and other sources in the home, including all contaminants; can either flow into a municipal sewer system or be treated with an onsite wastewater disposal system.
Waterborne finish: Finish for wood or other materials that uses water as the carrier, instead of an organic solvent; waterborne
finishes generally have much lower volatile organic compound (VOC) levels.
Whole-house (central) air conditioner: Air conditioning system that serves an entire house; cooled air is delivered through a system of ducts. See also room air conditioner.
Whole-wall R-value: Average R-value of a wall, taking into account the thermal bridging through wall studs.
Wind farm: Electricity-generating windmills grouped together to improve operation and maintenance efficiencies and economic performance; typically comprised of large windmills; the power is usually fed into the utility grid.
Wind power: Use of wind to generate electricity.
Worm bin: Alternative to a composting bin for kitchen scraps; worms digest organic waste, converting it into a rich soil.
Xeriscaping: Type of landscaping that requires little if any irrigation; suited to dry climates; generally relies on regionally adapted native plants.