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Passive House designed in a traditional cottage style has a simple and elegant
shape. It is a 3-bedroom, 1 living room, kitchen-dinning room, 1 office, 1
guest room, 3.5-bathroom, 140 square meters, two-story single family home with
a slopping roof

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"I follow in building the principles which nature has used in its domain" ~ Frank Lloyd Wright
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Green Glossary Terms

GREEN is a term widely used now to describe buildings designed and constructed with minimal negative impact to the environment and with an emphasis on conservation of resources, energy efficiency, and healthful interior spaces.

SUSTAINABILITY refers to the concept that new development must meet the needs of the present without compromising those of the future. Sustainability is measured in three interdependent dimensions: the environment, economics, and society—often referred to as the triple bottom line.
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Adapted Plants
Plants that reliably grow well in a given habitat with minimal attention from humans in the form of winter protection, pest protection, water irrigation, or fertilization once root systems are established in the soil. Adapted plants are considered to be low maintenance but not invasive. See also, native plants, invasive species.
Advanced Framing
This is a house-framing strategy/technique in which lumber use is optimized to save material and improving the energy performance of the building. Regular framing techniques leave a large amount of wasted wood that needs to be thrown away.
A device installed on sink faucets to reduce their water use and the energy needed to heat water. Faucet aerators, coupled with low-flow shower heads, can reduce your home's water use by 50%. If an aerator is already installed on your faucet, it will have its rated flow imprinted on the side. This should read 2.75 gpm (gallons per minute) or lower.
Air Barrier
Building assembly components/products that work as a system to restrict air flow through the building. An air barrier may or may not act as a vapor barrier. The air barrier can be on the exterior and/or the interior.
Air Handler
A fan that a furnace, 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 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 that serves as an interior air barrier in building assemblies.
Percentage of light reflected off a surface; a material with high albedo is highly reflective.
Ammonium Sulfate
Flame retardant commonly used in cellulose insulation. Borates are also used.
Mineral fiber once commonly used in building materials, including insulation, fireproof siding, and resilient flooring; a known human carcinogen causing lung cancer, asbestos is no longer used in the United States.
A potentially dangerous indoor air quality problem in which combustion gases escape into the house instead of going up the chimney.
Balanced Ventilation
Ventilation system in which fans exhaust stale indoor air and bring in fresh outdoor air in equal amounts; often includes heat recovery or heat and moisture recovery
Batch Solar Water Heater
Solar water heater in which potable water is heated where it is stored. Also referred to as an integral collector storage (ICS) solar water heater.
Glue used in manufacturing wood products, such as medium-density fiberboard (MDF), particleboard, and engineered lumber. Most binders are made with formaldehyde. Two types of binders include urea-formaldehyde binder and methyl diisocyanate (MDI) binder.
Bio-Based Material
Material made from living matter, like agricultural crops. Bio-based materials are usually biodegradable.
Theory developed by biologist Edward O. Wilson suggesting that humans have an innate affinity for nature.
Plant material such as trees, grasses and crops that can be converted to heat energy to produce electricity.
Wastewater generated from toilets and kitchen sinks that contains high levels of bacterial pollutant.See also, greywater.
Blower Door Test
Test used to determine a home’s airtightness. A powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower also exaggerates air leakage and permits a specialized contractor to find and seal the leakage areas.
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 Earth’s protective ozone later; except for extruded polystyrene, the industry has now switched to ozonesafe blowing agents.
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 for domestic uses through a tankless coil or an indirect water heater.
Built Environment
The man-made creation of or alterations to a specific area, including its natural resources. On a home site, this includes everything that has been construction.
Buildable Land
The portion of the site where construction can occur. When used in density calculations, the calculation for buildable land excludes public streets and other public rights of way, land occupied by non-residential structures, public parks, and land excluded from residential development by law.
Building Envelope
Exterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation. The envelope includes the house foundation, framed exterior walls, roof or ceiling, and insulation and air-sealing materials.
Capillary Forces
Forces that lift or pull water through porous materials, such as concrete.
Carbon Footprint
A measure of an individual's, family's, community's, company's, industry's, product's or service's overall contribution of carbon dioxide and other greenhouse gases into the atmosphere. It takes into account energy use, transportation methods and other means of emitting carbon. A number of carbon calculators have been created to estimate carbon footprints, including one from the U.S. Environmental Protection Agency.
Carbon Neutral
Achieving an overall neutral (zero) total carbon release, brought about by balancing the amount of carbon released with the amount sequestered. It is typically achieved by reducing energy use and obtaining energy from renewable sources combined with offsetting remaining emissions through such means as carbon offsets.
Carbon-Neutral House
House that, on an annual basis, does not result in a net release of carbon dioxide, which is a greenhouse gas that contributes to global warming, into the atmosphere.
Carbon Offset
The act of mitigating one's carbon emissions, often purchased through a carbon offset provider that uses the money for carbon-sequestering activities including tree planting, renewable energy, energy conservation and methane capture.
Catchment Area
The surface area on a roof that captures rainwater for direction into a rainwater harvesting system.
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.

Vessel for storing water, such as that collected with a rainwater-harvesting system.
Materials used to enclose a house, providing protection against weather.
Climate Change
The variation of the average temperatures, rainfall and other measures of global or regional climate over time, whether caused by natural processes, humanity's influence or a combination of both.
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.
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).
Process of testing a home after a construction or renovation project to ensure that all of the home’s systems are operating correctly and at maximum efficiency.
Composite Lumber
Lumber made from plastic (often high-density polyethylene) and wood fiber or other agricultural byproducts. Composite lumber often contains recycled content.
Composting System
Outdoor bins for converting vegetable scraps, garden trimmings, and other plant matter into a rich, high-organic-content soil amendment. An alternative for indoor use is a worm bin.
Composite Wood
A product consisting of wood or plant particles or fibers bonded together by a synthetic resin or binder. Examples include plywood, particle-board, OSB, MDF, composite door cores.
Concrete Masonry Unit (CMU)
Block made of concrete used for wall construction. The hollow cores can be filled with concrete to reinforce walls.
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.
Movement of heat from one place to another by physically transferring heated fluid molecules, usually air or water. Natural convection is the natural movement of that heat; forced convection relies on fans or pumps.
Cool Pavements
Materials and construction methods used in roads, driveways, parking lots, sidewalks, and other hard surfaces, which perform to reduce the absorption, retention and emittance of solar heat, thus minimizing urban heat island effect. Techniques to achieve cool pavements include the use of coloration, materials, porosity and other processes that promote solar reflectivity and cooling through augmented air filtration and evaporation.
Cradle to Grave
Term used to describe the environmental impact a product has from it’s creation to destruction.
Cripple Studs
Studs in a wall system that support headers above (and below) windows or doors; indiscriminately placed, these additional studs can 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 crosslinking (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 (EMFs).
Use of sunlight for daytime lighting needs.
Degree Day
Measure of heating or cooling requirements based on the average outdoor temperature. To calculate the number of heating degree days of 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 by subtracting the average outdoor temperature from 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. This is also known as a tankless water heater.
Double Wall
Construction system in which two layers of studs are used to provide a thicker-than-normal wall system to accommodate extra insulation. The two walls are often separated by several inches to reduce thermal bridging through the studs and to provide additional space for insulation.
Drain Back 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.
Drip Irrigation System
An irrigation system that slowly applies water to the root system of plants to maximize transpiration while minimizing wasted water and topsoil runoff. Drip irrigation usually involves a network of pipes and valves that rest on the soil or underground at the root zone.
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.
Duct Blaster
Calibrated air-flow measurement system developed to test the airtightness of forced-air duct systems. All outlets for the duct system except for the one being tested are sealed off and the system is either pressurized or depressurized; the work needed by the fan to maintain a given pressure difference provides a measure of duct leakage.
Electric-Resistance Heat
Heat provided by electricity in which high-resistance wires convert electric current directly into heat. See 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 cause cancer. Magnetic fields are stronger near current in which there is separation between the positive and neutral leads.
Embodied Energy
Energy that goes into making a product, including energy for transporting both the raw materials and the finished product.
The output of greenhouse gases and other pollutants from mechanical, industrial, transportation or other processes.
Endocrine Disruptor
Chemical that mimics natural hormones, such as estrogen, and may interfere with reproductive development or alter. Endocrine disruptors include such commonly used chemicals as phthalate plasticizers (used in PVC plastic), and bisphenol-A (used in epoxies and polycarbonate plastic).
Energy Efficient
Maximizing, or at least increasing, the ratio between productive output and energy use.
Energy Efficiency Rating (EER)
Operating efficiency of a room air-conditioner, measured in BTU’s of cooling output, divided by the power consumption in watthours; 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. A “modified energy factor” accounts for certain adjustments according to accepted test procedures.
Energy Star
Labeling system sponsored by the U.S. Environmental Protection Agency and the U.S. Department of Energy for labeling the most energy-efficient products on the market. The ratings apply to a wide range of products, from computers and office equipment to refrigerators and air-conditioners.
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.
Label from the Federal Trade Commission that lists the expected energy consumption of an appliance, heating system, or cooling system and compares consumption with other products in that category, The energy performance is based on specified operating conditions and average energy costs; 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.
Environmental Protection Agency. A U.S. government agency that oversees environmental laws and programs.
Evaporative cooler
Energy-efficient cooling system in which a fine mist of water is evaporated, lowering the air temperature. Evaporative coolers are most appropriate in dry climates, because 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.
Electric or hydronic heating or cooling element installed in a duct. In a highly energy-efficient home, fan coils in ventilation ducting can be used for heating or cooling the living space.
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, the material is becoming common as a siding material in North America.

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.
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.
Chemical found in many building products; most binders used for manufactured wood products are formaldehyde compounds. Reclassified by the United Nations International Agency for Research on Cancer (IARC) in 2004 as a known human carcinogen. 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, producing electricity, water vapor, and heat.
Transparent or translucent layer of window or door that transmits light. High-performance glazings may include multiple layers of glass or plastic, low emissivity (low-e) coatings, and low-conductivity gas fill.
Global Warming Potential
Measure of how a given mass of greenhouse gas is estimated to contribute to global warming compared against carbon dioxide, which is given a value of 1.0.
Gravity-Flush Toilet
Toilet whose flush is powered solely by the force of falling water. See also pressure-assist toilet.
Wastewater from a building that does not include flush-water from toilets or (as most commonly defined) water from kitchen sinks or dishwashers. In some places, graywater can be collected and used for subsurface irrigation.
Green Building
Design and construction of buildings that minimize impacts on the environment while helping 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.)
"Geothermal" literally means "earth heat." It is often used to describe two different types of alternative energy source. "True" geothermal energy is less commonly used. It draws on energy generated in the earth's core, about 4,000 miles below the surface, via steam and hot water produced inside the earth to heat buildings or generate electricity. More common are geothermal heating and cooling systems that capitalize on the relatively constant temperature of the ground to transfer heat. These systems don't actually use the geothermal energy generated deep within the earth; instead, they use a heat-transfer liquid to move heat from a few feet below ground into a house during cold months, and from the house to the ground during hot months.
Greenhouse Gas
A gas in the atmosphere that traps some of the sun's heat and preventing it from escaping into space. Greenhouse gases are vital for making the Earth habitable, but increasing greenhouse gases contribute to climate change. Greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, and ozone.
Wastewater generated from domestic processes such as washing dishes, laundry and bathing. Greywater makes up 50-80% of residential wastewater. Greywater can be used for irrigation, reducing water waste. See also, blackwater.
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 stand-alone 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), then insulated, sheathed, and finished.
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 Island Effect
Heat island effect The incidence of higher air and surface temperatures caused by solar absorption and re-emission from roads, buildings and other structures. See also, cool pavements.
Heat Pump
Heating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump.
Heat Distribution
System for delivering heat throughout a house. See forced-air heating and hydronic heating.
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.
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 the most rigorous standards for flush performance.
Home Performance Audit
An energy audit that also includes inspections and testing assessing moisture flow, combustion safety, thermal comfort, indoor air quality, and durability.
Home Run Plumbing System
Water distribution piping system in which individual plumbing lines extend from a central manifold to each plumbing fixture or waterusing appliance. The 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.
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.
Hydronic System
A heating or cooling system that relies on the circulation of water as the heat-transfer medium. A typical example is a boiler with hot water circulated through radiators.
Impervious Surface
Surface that does not permit stormwater runoff to infiltrate the ground. See also porous paving.
Indirect Water Heater
Water heater that draws heat from a boiler used for space heating. The boiler eats 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.
Insulated Concrete Form (ICF)
Hollow insulated forms, usually made from expanded polystyrene (EPS), used for building walls (foundation and above ground), that are stacked and stabilized and then filled with concrete, which provides the wall structure.
Integral Collector Storage (ICS) Solar Water Heater
Solar water heater in which potable water is heated in the same place it is stored.
Integrated Design
Building design in which different components of design, such as the building envelope, window placement and glazing, and mechanical systems, are considered together. High-performance buildings and renovations can be created cost effectively using integrated design, since higher costs in one place can often be paid for through savings elsewhere. For example, by improving the performance of the building envelope, the heating and cooling systems can be downsized or even eliminated.
International Standards Organization (ISO)
This international nongovernmental standard-setting body, founded in 1947, includes representatives of national standard development organizations, such as the American National Standards Institute (ANSI) in the U.S. ISO defines terms and develops worldwide standards that frequently become law or form the basis of industry norms.
Device for converting direct-current (DC) electricity into the alternating-current (AC) form required for most home uses. An inverter is necessary if home-generated electricity is to be fed into the electricity grid through a net-metering arrangements.
Kilowatt-Hour (kWh)
Measure of electricity consumption; a 100-watt light bulb burning for ten hours consumes 1 kWh.
Toxic heavy metal often found in paints made or applied before 1978. When renovating, follow proper lead-abatement procedures to avoid lead poisoning.
Life Cycle
Entire life of a product or material, from raw material acquisition through disposal.
Life-Cycle Assessment (LCA)
Examination of the environmental and health impacts of a product or material over its life cycle. LCA provides a mechanism for comparing different products and materials for green building.
Life-Cycle Cost (LCC)
Economic cost of a product or building over its expected life, including both first cost (purchase cost) and operating cost.
Light Pollution
Nighttime lighting that escapes into the night sky. Light pollution can interfere with the day-night patterns of ecosystems, disrupt the flights of migrating birds, interfere with sea turtle nesting in coastal areas, and hinder astronomical observation.
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. The fill boosts a window’s R-value and reduces its U-factor.
Low-emissivity (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. The coating 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.
Component that distributes the water in a home-run plumbing system. It has one inlet and many outlets, each of which feeds one fixture or appliance.
Mechanical Ventilation
Ventilation system using one or more fans to exhaust stale indoor air from a home as a way to ensure adequate indoor air quality. See exhaustonly ventilation and balanced ventilation.
Native Plants
Plants that have evolved within their own ecological habitats, and are not invasive within their own native ranges. Native plants provide food and shelter to indigenous wildlife, stabilize shorelines and fields, etc., growing in balance with surrounding plant and animal species. See also, adapted plants, invasive species.
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 electricity meter backward. 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.
Net-Zero Energy
Producing as much energy on an annual basis as one consumes on site, usually with renewable energy sources, such as photovoltaics or small-scale wind turbines. Calculating net-zero energy can be difficult, particularly in grid-tied renewable energy systems, because of transmission losses in power lines and other considerations.
Release of volatile chemicals from a material or product. See also volatile organic compounds.
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 that quickly delivers 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; including energy, maintenance, and repairs.
Operating Energy
Energy required to operate a device or building.
Passive Solar Heating
Building design in which solar energy provides a significant portion of the heating without fans or pumps; the building itself serves as the solar collector and heat storage system.
Payback Period
Length of time it takes for an investment to pay for itself. 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
Highest possible 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.
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.
Pier Foundation
Building foundation consisting of piers instead of continuous walls. Piers are resource-efficient because they avoid the need for continuous foundation walls.
Polyisocyanurate (polyiso)
Type of rigid foam insulation used in above-grade walls and roofs, typically with a foil facing on both sides. This kind of insulation 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. Both open-cell and higher-density closed-cell products are used.
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 Paving
A paving material that allows precipitation to percolate through and infiltrate the ground rather than contributing to stormwater runoff. Pavers can be asphalt, concrete, or porous grid.
Portland Cement
Building material made from limestone, gypsum, and shale or clay, which when mixed with water, 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.
Postconsumer Recycled Material
Material recovered from a waste product that has been in use by a consumer before being discarded. See also postindustrial recycled material.
Postindustrial (preconsumer) Recycled Material
Material recovered from the waste stream of an industrial process that has not been placed in use. See also postconsumer recycled material.
Potable Water
Water considered safe for drinking and cooking.
Any silicon or silicon-aluminum material - which when finely divided and mixed with moisture, reacts with calcium hydroxide to form a cementitious compound. Common examples of pozzolans include fly ash, blast furnace slag, volcanic ash, silica fume, and rice hull ash.
Pressure-Assist Toilet
Toilet that uses air pressure, generated as the toilet tank refills, to produce a more forceful flush; some high-efficiency toilets (HETs) rely on pressure-assist technology.
Measure of resistance to heat flow; the higher the R-value, the lower the heat loss. R-value is 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; alternatively, the tubing can be installed on the underside of wood subflooring, although the benefit of thermal mass is lost.
Movement of energy via electromagnetic waves.
Rain Garden
Swales (low tracts of land that water flows to) with vegetation designed to absorb rain water in ways that reduce stress on storm drains and replenish ground water.
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 one-quarter to three-quarters of an inch.
Raised Heel Truss
Preconstructed roof truss designed to allow room at the eaves (above exterior walls) for large amounts of insulation. (Standard roof trusses have sufficient depth for adequate insulation near the eaves.)
The collection, reprocessing, marketing and use of materials that were diverted or recovered from the solid waste stream.
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.
Compound used in refrigerators, airconditioners, and heat pumps to transfer heat from one place to another (using the Rankine cycle), thus cooling or heating a space. Most refrigerants today are hydrochlorofluorocarbons (HCFCs), which deplete the ozone layer.
Renewable Energy
Thermal or electrical energy produced using solar, wind, hydropower, or biomass energy sources.
A measure of thermal resistance (the number of watts that will be lost per square meter at a given temperature difference). The inverse of U value (i.e., R=1/U).
Seasonal Energy Efficiency Ratio (SEER)
Energy performance rating of a whole-house (central) air conditioner or heat pump operating in the cooling mode, calculated as the ratio of the estimated seasonal cooling output divided by the seasonal power consumption in an average climate.
Material, usually plywood or oriented-strand board (OSB) but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses. Siding or roofing installed on the sheathing, sometimes over strapping to create a rainscreen.
Solar Collector
Device for capturing solar energy and transferring heat to water or air that circulates through it.
Solar Gain
Sunlight entering a building. A passive solar direct-gain system uses solar gain.
Solar Heat Gain Coefficient (SHGC)
The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.
Solar Window Screens
A mesh screen that is used to block insects as well as light and heat from the sun.
Space Planning
Process of converting the needs expressed by the client into the drawings and supporting documentation that outline the plan for the team
Runoff from Rain that is either carried off site in storm sewers or allowed to infiltrate the ground; stormwater can be reduced through the use of porous paving and other infiltration strategies.

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.
Sun Tempering
Practice of using a modest area of south facing windows to provide limited passive solar heating to a house.
To insulate extremely well. A house with very efficient windows and tight construction results in very low heating and cooling costs.
Sustainable refers to products and techniques that are renewable or recyclable and therefore minimize the natural resources they use.
Low area of ground used for drainage and oftenthe infiltration of stormwater.
Tankless Coil
Heat exchanger used for heating water that is integrated into a boiler. Effective in the winter months when the boiler is operating for space heating, tankless coils waste energy in warmer months, since they require the boiler to fire up every time hot water is drawn.
Tankless Water Heater
Tankless water heaters heat water as it flows through the device. They do not retain any water internally except for what is in the heat exchanger coil. Tankless heaters are often installed throughout a household at more than one point-of-use, or larger models may still be used to provide all the hot water requirements for an entire house. The chief advantages of tankless water heaters are a continuous flow of hot water and energy savings (as compared to a limited flow of continuously heating hot water from conventional tank water heaters).
Unit of heat equal to 100,000 British thermal units (Btus), commonly used to measure natural gas consumption.
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 Envelope
The thermal enclosure created by the building exterior and insulation. Improving the thermal envelope is one of the most important aspects to creating an energy efficient home.
Thermal Mass
Heavy, high-heat-capacity material that can absorb and store a significant amount of heat; used with a passive solar heating system to keep the house warm at night.
Thermosiphon Solar Water Heater
Solar water heater that operates passively (through natural convection), circulating water through a solar collector and into an insulated storage tank situated above the collector. Pumps and controls are not required.
Top Plate
Wood framing member that forms the top of a wall. In advanced framing, a single top plate is often used in place of the more typical double top plate.
Tubular Skylight
Round skylight that transmits sunlight down through a tube with internally reflective walls, even through an attic space to deliver daylighting through a ceiling light diffuser. Most tubular skylights are 12 to 16 inches in diameter and deliver daytime lighting comparable to several 100-watt incandescent light bulbs.
Measure of the heat conducted through a given product or material calculated as the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every one degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value.
United States Green Building Council (USGBC)
Organization devoted to promoting and certifying green buildings. USGBC created the LEED rating systems.
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. Although unvented gas heaters burn very efficiently, indoor air quality experts strongly recommend against their use because combustion gases, including high levels of water vapor, are released into the house.

U Value (U factor)
A measure (often used for windows) of thermal conductivity that is the inverse of R value. A lower U value means a more energy efficient window.
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 Profile
The relative individual component and total combined vapor permeability of building assemblies. The vapor profile addresses not only how the assembly protects itself from getting wet by vapor diffusion, but also how it dries the assembly gets wet.
Vapor Retarder
Layer that inhibits vapor diffusion through a building envelope. Examples include polyethylene sheeting, foil facing, kraft paper facing on batt insulation, and low-permeability paints. Most building codes define a vapor retarder as 1 perm or less, with many common vapor retarders being significantly less than 1 perm. Note that many building scientists prefer a focus on the vapor profile of a building assembly rather than just the individual vapor permeability of the designated vapor retarder.
Variable Air Volume (VAV) Air Handler
System for controlling an HVAC system in which the volume of air provided to conditioned space is varied to control comfort.
Vegetated Roof
A roof partially or fully covered by vegetation. By creating roofs with a vegetated layer, the roof can counter-act the heat island effect as well as provide additional insulation and cooling during the summer.
Replacement of stale indoor air with fresh outdoor air, usually with fans but sometimes naturally through building design elements. See also heat recovery ventilator.
Waste Management Plan
Plan that addresses the collection and disposal of waste generated during construction or renovation, usually including the collection and storage of recyclable materials.
Used water from toilets, showers, sinks, dishwashers, clothes washers, and other sources in the home, including all contaminants, which can either flow into a municipal sewer system or be treated with an onsite wastewater disposal system. See also graywater.
Program developed and administered by the U.S. Environmental Protection Agency to promote and label water-efficient plumbing fixtures.
Cost-effective energy efficiency measures for existing residential and multifamily housing. When weatherization includes the house as a system, it is often called whole-house weatherization.
Type of landscaping that requires little if any irrigation, is suited to dry and drought-prone climates, and generally relies on regionally adapted native plants.

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