Appraiser's Glossary of Green Building Terms N - Z
People who are interested in green building are typically interested in minimizing the amount of plastics and toxins they expose themselves and their families to. For these people, natural materials like wood, cotton, wool, and plant-based materials are considered preferable to highly processed chemicals like vinyl.
Ventilation design that uses existing air currents on a site and natural convection to move and distribute air through a structure or space. Strategies include placement and operability of windows and doors, thermal chimneys, landscape berms to direct airflow on a site, and operable skylights. (Source: City of Seattle Green Building Glossary)
A metering and billing arrangement that allows on-site generators to send excess electricity flows to the regional power grid. These electricity flows offset a portion of the electricity flows drawn from the grid. For more information on net metering in individual states, visit the U.S. DOE Green Power Network website. (Source: City of Seattle Green Building Glossary)
Net-zero Energy Homes
In these homes, solar, wind and geothermal systems generate enough energy to power the entire house, making the effective power bill zero over the course of a year. These homes are typically tied into the power grid so that during times when home is not producing power (such as a solar-powered home at night), power comes from the grid. Though when the sun is shining bright, more energy is being generated than is being used. At the end of the year, the net is zero. Whole tracts of these homes have been built in Las Vegas and other places. It is conceivable that eventually all new homes will be net-zero energy homes.
Energy derived from depletable fuels (oil, gas, coal) created through lengthy geological processes and existing in limited quantities on the earth.
Release of volatile chemicals from a product or assembly. Many chemicals released from materials impact indoor air quality and occupant health and comfort. Offgassing can be reduced by specifying materials that are low- or no-VOC and by avoiding certain chemicals (e.g., urea formaldehyde) entirely. Controlling indoor moisture, and specifying pre-finished materials, can also reduce offgas potential. (Source: City of Seattle Green Building Glossary)
Orientation of a structure for controlled solar gain is essential to the success of passive and active solar design elements. Sun charts and software assist in orienting a building for maximum solar benefit. Designing for solar considerations can substantially reduce both heating and cooling. (Source: City of Seattle Green Building Glossary)
Architectural elements on roofs and above windows that function to protect the structure from the elements or to assist in daylighting and control of unwanted solar gain. Sizing of overhangs should consider their purpose, especially related to solar control. (Source: City of Seattle Green Building Glossary)
Strategies for using the energy of the sun to heat (or cool) a space, mass, or liquid. Passive solar strategies use no pumps or controls to function. A window, oriented for solar gain and coupled with massing for thermal storage (e.g., a Trombe wall) is an example of a passive solar technique. (Source: City of Seattle Green Building Glossary)
A truly green home should include recycled materials. The most common recycled materials one might find in a home include composite decking like Trex, which is made from plastic (such as ground up trash bags) and wood (such as pallets). Some carpeting, like Interface, is made from old carpeting that has been recycled. Points are given in the LEED program for recycled products. A differentiation should be made between post-consumer and post-industrial materials. The former is considered more green.
One of the major tenets of green building is considering the life cycle of the materials used to build a home. It was once known as cradle-to-grave awareness. In other words, what will happen with this material after it has served its function? Will it end up in a landfill? Can it be recycled? The current thinking is to pay attention to cradle-to-cradle aspects of the product. For instance, lumber off-cuts used in a house can be recycled for use in other products, or ground into chips. Excess drywall can be ground at the jobsite to be used as a soil amendment. Interface carpeting does not end up in the landfill, but is sent back to the factory to be recycled into more carpeting.
As the planet becomes more populated and awareness grows that the earth is not an unlimited repository of raw materials, it becomes necessary to be conservative with materials. That includes harvesting wood from sustainably maintained forests, for instance, and using tile or flooring made from recycled materials or quickly renewed materials. Bamboo is a quickly renewed material, as is cork. As consumers become more aware of the limits of the natural resources of the earch, there is every reason to expect that a house that has bamboo floors, or cork floors, or tile or counters made of recycled materials will grow in value.
Roofing Material and Color
Durability is the key word in green building, the basis on which all other green features rest. So a roof with a 50-year lifespan is much greener than one with a 10-year estimated lifespan. As landfills grow and teeter and expand, consumers will become more aware of the social and personal cost of buying and installing cheap materials like roofing.
A unit of thermal resistance used for comparing insulating values of different materials; the higher the R-value, the greater its insulating properties
Solar Electric Systems
Of all the improvements that make a house green? solar-generated electricity is probably the most profound in terms of the environmental impacts. However, oddly enough, these systems rarely bring added value to a home. People who have installed these systems are naturally disappointed in this. As energy prices soar, however, there is every reason to expect that solar power systems will become highly prized. Also, costs of these systems are expected to fall by 2010, so you could expect more homeowners to invest in them.
There are two different types of solar-power systems: off-grid or grid-tied. In the past, back in the 1970s for instance, there was no such thing as grid-tied. All systems involved solar panels that charged up deep-cell batteries, and an inverter that turned the 12-volt battery power into 120-volt power that can be used in a home. Today, most systems are grid-tied, which means there are no batteries to maintain. In grid-tied systems, the power generated by the system is used by the home, and the excess is fed back into the power grid, and the homeowner is paid for that. When no energy is being generated, such as on cloudy days or at night, power flows again from the grid to the home.
Solar Heat Gain Coefficient
Solar Heat Gain Coefficient (SHGC) measures how well a product blocks heat caused by sunlight. The SHGC is the fraction of incident solar radiation admitted through a window (both directly transmitted and absorbed) and subsequently released inward. SHGC is expressed as a number between 0 and 1. The lower a window's solar heat gain coefficient, the less solar heat it transmits in the house. (Source:National Fenestration Rating Council)
Straw Bale Construction
Alternative building method using bales of straw for wall systems. The method uses an agricultural waste product in place of diminishing dimensional lumber, and achieves high insulation values. It is a building method most appropriate for regions with relatively little precipitation. (Source: City of Seattle Green Building Glossary)
Structural Insulated Panel (SIP)
Manufactured panels consisting of a sandwich of polystyrene between two layers of engineered wood paneling. Can be used for walls, roof, or flooring, and result in a structure very resistant to air infiltration. (Source: City of Seattle Green Building Glossary)
System capacity is a measurement of the total amount of heat or cooling a furnace, heat pump or air conditioner can produce in one hour. This amount is reported in Btu/hr on the nameplate of the equipment. (Source: Lawrence Berkeley National Laboratory)
Method of increasing the thermal performance of a material or assembly by reducing conductive heat loss. By inserting a less thermally conductive material in a material or assembly that bridges conditioned and unconditioned space, the conductive path is reduced or broken. An example is the thermal break featured in aluminum-framed windows. (Source: City of Seattle Green Building Glossary)
Unwanted heat loss or gain due to conduction through a material. An example of thermal bridging is heat loss that occurs with structural steel framing that is insufficiently insulated between conditioned and unconditioned space. (Source: City of Seattle Green Building Glossary)
U-Factor or U-Value
U-factor measures how well a product prevents heat from escaping. The rate of heat loss is indicated in terms of the U-factor (U-value) of a window assembly. U-Factor ratings generally fall between 0.20 and 1.20. The lower the U-value, the greater a window's resistance to heat flow and the better its insulating value. (Source: National Fenestration Rating Council)
Before the energy crisis of the 1970s, at which time new energy standards required homes to be sealed up better to conserve energy, ventilation was not such a big issue. Houses leaked energy and air, especially through old wood-framed windows, and all was well. But since houses have become sealed up better -- with air and vapor barriers such as Tyvek and other house wraps, and with vinyl windows and door sealing and other measures -- added effort has to be taken to ensure a certain number of air exchanges per hour. Houses with whole-house ventilation systems are more in line with green building (which means the house is comfortable and healthy) than those without.
Visible Transmittance (VT) measures how much light comes through a product. The visible transmittance is an optical property that indicates the amount of visible light transmitted. VT is expressed as a number between 0 and 1. The higher the VT, the more light is transmitted. (Source: National Fenestration Rating Council)
VOC stands for volatile organic compound. This could also be expressed as volatile chemical compound. VOCs are toxic chemicals known to have what the EPA calls adverse health effects. In other words, they make us sick. VOCs are chemicals that vaporize from commonplace products as paint, sealants and carpeting. You know that new-carpeting smell? That is chemicals offgassing from modern materials, and this offgassing can continue for years. As consumers grapple with more and more immune-system failures, lung problems, allergies and so on, awareness of low-VOC and no-VOC materials will likely grow and become valued.
Design strategy for reducing the amount of contaminants introduced into an interior space by providing grating or other material to remove contaminants from shoes. Significant portions of contaminants in a building are brought in this way, impacting indoor environmental quality. (Source: City of Seattle Green Building Glossary)
Water Heating, Solar
From the U.S. Dept. of Energy: Solar water heaters -- also called solar domestic hot water systems -- can be a cost-effective way to generate hot water for a home. They can be used in any climate, and the fuel they use -- sunshine -- is free. Solar water heating systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don't.
Most solar water heaters require a well-insulated storage tank. Solar storage tanks have an additional outlet and inlet connected to and from the collector. In two-tank systems, the solar water heater preheats water before it enters the conventional water heater. In one-tank systems, the back-up heater is combined with the solar storage in one tank. On average, if a house has a solar water heater, the water heating bills should drop 50% to 80%. Also, because the sun is free, the homeowners are protected from future fuel shortages and price hikes. (More info: U.S. Dept. of Energy)
Water Heating, Tankless
These water heaters are called tankless, on-demand, or instantaneous water heaters. The concept is this: Instead of heating water and storing it in a tank, these heaters use a high-powered gas burner or electric element to heat the water the moment it is used. Once an exotic rarity in homes, they are becoming so mainstream that they are offered by such manufacturers as GE and Bosch. Whereas not too long ago, homeowners might have scratched their heads at a small metal box in place of a water heater tank, they will more and more come to recognize these as energy savers. That is because in a tank system, the water slowly cools down and then has to be reheated, which wastes water. Of course, the better insulated the tank, the less the water will cool off.
According to the U.S. Dept. of Energy: For homes that use 41 gallons or less of hot water daily, demand water heaters can be 24% to 34% more energy efficient than conventional storage tank water heaters. They can be 8% to 14% more energy efficient for homes that use a lot of hot water -- around 86 gallons per day. Greater energy savings of 27% to 50% can be achieved if a demand water heater is installed at each hot water outlet. (Read more: U.S. Dept. of Energy)
The process of reducing the leaks of heat from or into a building. It may involve caulking, weather-stripping, adding insulation, and other similar improvements to the building shell.
Systems that convert air movement into mechanical or electrical energy. Driven by the wind, turbine blades turn a generator or power a mechanical pump
Landscaping design for conserving water that uses drought-resistant or drought-tolerant plants.