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153 Green Building Acronyms and Initials

If you're bewildered by the jargon, here's a list to help you decipher all those abbreviations

Posted on Jan 8 2014 by Allison A. Bailes III, PhD

Acronyms and initials (let's call that AI, for short, not to be confused with the other AI, which stands for artificial intelligence, or AIA, which stands for American Institute of Architects) are part of the jargon of every field. Our field, whether you call it building science, green building, home performance, or something else, is no exception. So, a few years ago I started putting together a list that I now include in the manuals that we give out in our training classes.

I'm up to 153 total lines in my list, which our students find helpful in sorting out all the jargon that's new to them. When you first come into this field and start getting the barrage of ACH50, HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building., COPEnergy-efficiency measurement of heating, cooling, and refrigeration appliances. COP is the ratio of useful energy output (heating or cooling) to the amount of energy put in, e.g., a heat pump with a COP of 10 puts out 10 times more energy than it uses. A higher COP indicates a more efficient device . COP is equal to the energy efficiency ratio (EER) divided by 3.415. , HDDThe difference between the 24-hour average (daily) temperature and the base temperature for one year for each day that the average is below the base temperature. For heating degree days, the base is usually 65 degrees Fahrenheit. For example, if the average temperature for December 1, 2001 was 30 degrees Fahrenheit, then the number of heating degrees for that day was 35., WRB, and more thrown at you, it's good to have somewhere you can look these things up.

Also, if two AI have the same definition, I included them on the same line. For example, SHR and SHF both refer to the same quantity, even though one uses the word fraction and the other ratio.


GBA Glossary

When a single AI has two different definitions, however, I put them on separate lines. The only one I have like that right now is CO, which could stand for carbon monoxide or certificate of occupancy.

Anyway, I'm sure you're dying to find out what RTFM stands for, so let's get on with it. Below is a table of my 153 acronyms and initials. If you want to download the list, see the link below the table.

Acronym What it stands for
AAC autoclaved aerated concrete
ABAA Air BarrierBuilding 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. Association of America
ACCA Air Conditioning Contractors of America
ACH50 air changes per hour at 50 Pascals
ACHnat air changes per hour natural
ACI Affordable Comfort Inc.
ADA another damn acronym (although this would really be initials)
ADA Americans with Disabilities Act
ADC Air Distribution Council
AFUEAnnual 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. annualized fuel utilization efficiency
AGW above-grade wall
AHJ authority having jurisdiction
AHRI Air Conditioning, Heating, and Refrigeration Institute
AHU air handler unit
ANSIAmerican 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. American National Standards Institute
APHN American Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. Network
ASHP air-source heat pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps.
ASHRAEAmerican 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. Amer. Soc. of Heating, Refrigerating, and Air-conditioning Engineers
ASTMAmerican 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. American Society for Testing and Materials
BA Building America
BAS building airflow standard
BCAP Building Codes Assistance Project
BOP Builder Option Package
BPI Building Performance Institute
BS building science
BSC Building Science Corporation
BTL building tightness limit
BTUBritish 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. One Btu is equivalent to 0.293 watt-hours or 1,055 joules. British Thermal Unit
CAZ combustion appliance zone
CCF hundred cubic feet
CDD cooling degree days
CFA conditioned floor area
CFLCompact fluorescent lamp. Fluorescent lightbulb in which the tube is folded or twisted into a spiral to concentrate the light output. CFLs are typically three to four times as efficient as incandescent lightbulbs, and last eight to ten times as long. CFLs combine the efficiency of fluorescent light with the convenience of an Edison or screw-in base, and new types have been developed that better mimic the light quality of incandescents. Not all CFLs can be dimmed, and frequent on-off cycling can shorten their life. Concerns have been raised over the mercury content of CFLs, and though they have been deemed safe, proper recycling and disposal is encouraged. compact fluorescent lamp
cfm cubic feet per minute
cfm50 cubic feet per minute at 50 Pascals
CHP combined heat & power
CO carbon monoxide
CO certificate of occupancy
CO2 carbon dioxide
COP coefficient of performance
CYA cover your ass
CZ climate zone
DIY do it yourself
DOEUnited States Department of Energy. Department of Energy
ECM electronically commutated motor
EEM energy efficient mortgage
EER energy efficiency ratio
EF energy factor
EFL Environments for Living(EFL). A green building program that focuses on building science to improve home energy efficiency and comfort. EFL is administered by Masco Contractor Services.
EIA Energy Information Administration
EIM Energy Improvement Mortgage
ELA envelope/enclosure leakage area
ELR Envelope/Enclosure Leakage Ratio
EPA Environmental Protection Agency
EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest. expanded polystyrene
EqLA equivalent leakage area
ERV(ERV). The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV. energy (or enthalpy) recovery ventilator
ES / ESTAR Energy StarLabeling system sponsored by the 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.
ES V3 Energy Star version 3
FHA U.S. Federal Housing Authority
FLA four letter acronym or five letter acronym
FROG finished room over garage
GBA Green Building Advisor
GC general contractor
GSHP ground-source heat pumpHome heating and cooling system that relies on the mass of the earth as the heat source and heat sink. Temperatures underground are relatively constant. Using a ground-source heat pump, heat from fluid circulated through an underground loop is transferred to and/or from the home through a heat exchanger. The energy performance of ground-source heat pumps is usually better than that of air-source heat pumps; ground-source heat pumps also perform better over a wider range of above-ground temperatures.
GWP global warming potential
HDD heating degree days
HEPA high efficiency particulate air
HERSIndex or scoring system for energy efficiency established by the Residential Energy Services Network (RESNET) that compares a given home to a Home Energy Rating System (HERS) Reference Home based on the 2006 International Energy Conservation Code. A home matching the reference home has a HERS Index of 100. The lower a home’s HERS Index, the more energy efficient it is. A typical existing home has a HERS Index of 130; a net zero energy home has a HERS Index of 0. Older versions of the HERS index were based on a scale that was largely just the opposite in structure--a HERS rating of 100 represented a net zero energy home, while the reference home had a score of 80. There are issues that complicate converting old to new or new to old scores, but the basic formula is: New HERS index = (100 - Old HERS score) * 5. Home Energy Rating System
HOT2000 A type of Canadian energy modeling software
HP home performance
HPwES Home Performance with Energy StarA residential weatherization program jointly administered by the U.S. Department of Energy and the U.S. Environmental Protection Agency. The Home Performance With Energy Star program connects homeowners interested in improving the energy performance of their homes with contractors trained to assess home performance and perform energy retrofit work.
HRV(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; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. heat recovery ventilator
HSPF heating season performance factor
HUD U.S. Department of Housing and Urban Development
HVAC Heating, Ventilating, & Air Conditioning
IAQIndoor air quality. 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. indoor air quality
ICAT insulation contact, air tight (designation for recessed can lights)
ICC International Code Council
ICFInsulated concrete form. Hollow insulated forms, usually made from expanded polystyrene (EPS), used for building walls (foundation and above-ground); after stacking and stabilizing the forms, the aligned cores are filled with concrete, which provides the wall structure. insulated concrete form
IEA International Energy Agency
IECC International Energy Conservation Code. International Energy Conservation Code
IEQ indoor environmental quality
IR infrared
IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code. International Residential Code
IREC Interstate Renewable Energy Council
iwc inches of water column (pressure unit)
iwg inches of water gauge (pressure unit, same as iwc)
KISS keep it simple, stupid
LBL Lawrence Berkeley Laboratory (old name, still used by some)
LBNL Lawrence Berkeley National Laboratory
LCALife-cycle assessment. 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 analysis
LEDLight-emitting diode. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed. light emitting diode
LEEDLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. Leadership in Energy & Environmental Design
LEED AP LEED Accredited Professional
MEC Model Energy Code
MERV Minimum Efficiency Reporting Value
NAHBNational Association of Home Builders, which awards a Model Green Home Certification. National Association of Home Builders
NAPHN North American Passive House Network (a.k.a. APHN)
NASEO National Association of State Energy Offices
NATE North American Technician Excellence
NCI National Comfort Institute (not to be confused with Comfort Institute)
NIST National Institute of Standards and Technology
NPP neutral pressure plane
NPV net present value
NREL National Renewable Energy Laboratory
NZE Net ZeroProducing 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. Energy
OCEAN Online Code Environment and Advocacy Network
OEM original equipment manufacturer
ORNL Oak Ridge National Laboratory
OSB oriented strand board
OVE Optimal Value Engineering (includes advanced framingHouse-framing techniques in which lumber use is optimized, saving material and improving the energy performance of the building envelope.)
PDW pre-drywall
PHAUS Passive House Alliance U.S.
PHIUS Passive House Institute U.S.
PM project manager
PPE personal protective equipment
PSC permanent split capacitor
PTAC packaged terminal air conditioner
PTHP packaged terminal heat pump
PV photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow.
PV present value
QA quality assurance
QAD Quality Assurance Designee
RECS Residential Energy Consumption Survey
RESNET Residential Energy Services Network
RH relative humidity
RTFM read the friendly manual
SDO Standards Development Organization (ANSI designation)
SEER(SEER) The efficiency of central air conditioners is rated by the Seasonal Energy Efficiency Ratio. The higher the SEER rating of a unit, the more energy efficient it is. The SEER rating is Btu of cooling output during a typical hot season divided by the total electric energy in watt-hours to run the unit. For residential air conditioners, the federal minimum is 13 SEER. For an Energy Star unit, 14 SEER. Manufacturers sell 18-20 SEER units, but they are expensive. seasonal energy efficiency ratioSeasonal Energy Efficiency Ratio (SEER) is the total cooling output (in BTU) of an air conditioner or heat pump during its normal annual usage period divided by its total energy input (in Watt-hours) during the same period. The units of SEER are Btu/W·h. SEER measures how efficiently a residential central cooling system operates over an entire cooling season. The relationship between SEER and EER depends on location, because equipment performance varies with climate factors like air temperature and humidity.
SFBE square footage of building enclosure
SHF or SHR sensible heat fraction (or ratio)
SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. solar heat gain coefficient(SHGC) The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.
SIP(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. structural insulated panel
SIPA Structural Insulated Panel Association
SIR savings investment ratio
SMACNA Sheet Metal and Air Conditioning Contractors' National Association
SPF spray polyurethane foam
SPFA Spray Polyurethane Foam Association
SWAG scientific wild-ass guess
TESP total external static pressure
TLA three letter acronym
TXV or TEV thermal expansion valve
USGBCUnited States Green Building Council (USGBC). Organization devoted to promoting and certifying green buildings. USGBC created the LEED rating systems. U.S. Green Building Council
VOC volatile organic compound
VRF variable refrigerant flow
VRV variable refrigerant volume
WRB water-resistive barrierSometimes also called the weather-resistive barrier, this layer of any wall assembly is the material interior to the wall cladding that forms a secondary drainage plane for liquid water that makes it past the cladding. This layer can be building paper, housewrap, or even a fluid-applied material. (not weather-resistant barrier)
wrt with respect to
WUFI Wärme-und Feuchtetransport instationär
XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. extruded polystyrene
ZEB zero energy building (should be 'net' zero)
ZPD zone pressure diagnostics

Sorry. No definitions for the AI above. The purpose of this list is just to help people decode the letters when they hear or read them. Some of these terms are defined in the GBA glossary.

Get the full list

If you'd like the list of what is currently 153 acronyms and initials in both pdf and MS Excel formats, go here: Get the List!.

I hope you find it useful. If you're relatively new to the field, this list can be quite handy. If you've been in the field for a while, you probably know all or most of what's here, but maybe you have some others that you think I should add. Let me know.

Allison Bailes of Decatur, Georgia, is a speaker, writer, energy consultant, RESNET-certified trainer, and the author of the Energy Vanguard Blog. You can follow him on Twitter at @EnergyVanguard.


AI isn't an acronym because if you tried to say it, someone might dial 911. To be an acronym, it'd have to make a nice word-like sound. Something like IMP (Insulation Manufacturers and Partners) or LUST (leaking underground storage tank), for example. (Only one of those is something I made up, btw.) AI isn't an abbreviation either, which is usually a shortened version of a single word. And don't get me started on contractions! No, AI is a set of initials, which is usually the word people should use when they call something an acronym.

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Image Credits:

  1. tikitoy998 from - Creative Commons license

Jan 14, 2014 2:19 PM ET

double jeopardy
by Hobbit _

The amusing thing is that some mechanism of GBA tries to identify
glossary terms in posted text and insert some form of the
definition in a way that isn't clear to me, perhaps it's
supposed to be a mouse-over that expands a pop-up or the like.
Reading GBA with a text-only or bare-bones browser as I usually
do, things get confusing because that text simply shows up inline
right after the term in question without even any separation
added. It's theoretically smart enough to do that only on the
first instance per post of the term and not all of them, but
makes for amusing reading sometimes.

Now imagine what happens when I read this article!

I see similar glossary mechanisms on other forums, but the terms
are simply highlighted clickable links that readers can *optionally*
follow if they want a definition. Hopefully the coming website
revamp can also present glossary references in a slightly less
stuffed-down-your-throat fashion, which will also cause slightly
less text to be sent out per page anyway.


Jan 15, 2014 8:41 AM ET

Response to Hobbit
by Martin Holladay

Thanks for letting us know about one more glitch in the design of our GBA website. I really appreciate the feedback. I have added your suggestion to a long list of hoped-for improvements to the GBA web site, and I will be sharing the list with our technical team.

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