Ammoniacal copper arsenate.
One of several varieties of toxic pesticides used in pressure-treated wood; see also CCA (chromated copper arsenate).

ACH stands for Air Changes per Hour. This is a metric of house air tightness. ACH is often expressed as ACH50, which is the air changes per hour when the house is depressurized to -50 pascals during a blower door test. The term ACHn or NACH refers to "natural" air changes per hour, meaning the rate of air leakage without blower door pressurization or depressurization. While many in the building science community detest this term and its use (because there is no such thing as "normal" or "natural" air leakage; that changes all the time with weather and other conditions), ACHn or NACH is used by many in the residential HVAC industry for their system sizing calculations.

ACQ is a water-based wood preservative alternative to CCA for preserving wood that prevents decay from fungi and insects. There are four standardized ACQ formulations, Types A, B, C, and D. The different formulations allow achieving compatibility with different wood species and applications. All ACQ types contain 2 active ingredients which may vary within the following limits: copper oxide (62%-71%), which is the primary fungicide and insecticide, and a quaternary ammonium compound (29%-38%), which provides additional fungicide and insect resistance properties.

House-framing techniques in which lumber use is optimized, saving material and improving the energy performance of the building envelope.

A U.S. Environmental Protection Agency (EPA) program to promote the construction of "better than Energy Star" homes.

A proposed U.S. Environmental Protection Agency (EPA) program to promote the construction of “better than Energy Star” homes. The proposal calls for builders to comply with a “Builder Option Package” of measures including superinsulated walls, triple-glazed windows, ducts within the conditioned space, compact duct layout, a furnace with sealed plenums and a variable-speed energy-efficient blower motor, an efficient hot water distribution system, and a solar water heater or heat-pump desuperheater.

Annual Fuel Utilization Efficiency. Widely-used measure of the fuel 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. Furnaces sold in the United States must have a minimum AFUE of 78%. High ratings indicate more efficient equipment.

Building assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both.

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.

In terms of solar energy, the angle that the sun's rays make with an imaginary line perpendicular to a surface. The angle of incidence determines the intensity of the energy that any surface “sees.”

(AFUE) Widely-used measure of the fuel 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. Furnaces sold in the United States must have a minimum AFUE of 78%. High ratings indicate more efficient equipment.

American National Standards Institute. National nonprofit membership organization that coordinates development of national consensus standards. Accreditation by ANSI signifies that the procedures used meet the Institute’s essential requirements for openness, balance, consensus, and due process.

APA-The Engineered Wood Association.
Nonprofit trade association for manufacturers of engineered wood products, including glue-laminated timber (glulams), composite panels, wood I-joists, and laminated veneer lumber (lvls). APA and APA EWS (Engineered Wood Systems) trademarks identify products that meet the organization's manufacturing and performance guidelines. Formerly known as the American Plywood Association.

Inert (chemically stable) gas, which, because of its low thermal conductivity, is often used as gas fill between the panes of energy-efficient windows.

Mineral fiber once commonly used in many building materials, including insulation, fireproof siding, and resilient flooring. Inhalation of invisible asbestos fibers can lead to chest and abdominal cancers as well as scarring of the lungs. The use of asbestos in some products has been banned by the EPA and the U.S. Consumer Products Safety Commission; manufacturers also have adopted voluntary limitations on its use. When found in older buildings (most commonly in floor tiles, pipe and furnace insulation, or asbestos shingles), the product's friability is a major determinant in how it must be handled during renovations. More information: http://www.epa.gov/iaq/asbestos.html

American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).
International organization dedicated to the advancement of heating, ventilation, air conditioning, and refrigeration through research, standards writing, publishing, and continuing education. Membership is open to anyone in the HVAC&R field; the organization has about 50,000 members.

A standard for residential mechanical ventilation systems established by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Among other requirements, the standard requires a home to have a mechanical ventilation system capable of ventilating at a rate of 1 cfm for every 100 square feet of occupiable space plus 7.5 cfm per occupant.

The American Society of Interior Designers is a trade association representing the interior design professional community. ASID partnered with USGC to develop the REGREEN program, a green residential remodeling program (see www.regreenprogram.org).

American Society for Testing and Materials. Not-for-profit international standards organization that provides a forum for the development and publication of voluntary technical standards for materials, products, systems, and services. Originally the American Society for Testing and Materials.