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Glossary



Air Changes per Hour at 50 Pascals (ACH50) - An expression of ventilation rates or air infiltration - the number of times in an hour that the equivalent of home's entire air volume is exchanged with outside air.


Air barrier - The portion of the building enclosure which controls air flow between a conditioned space (indoors) and an unconditioned space (outdoors). Comprised of low air permeance materials that are continuous over the entire building enclosure. These air barriers can be located on the interior or exterior of the building.


Air barrier system - The assembly of components used in building construction to create a plane of air tightness throughout the building envelope and to control air leakage. Component elements include such things as windows, doors and service entries inserted and sealed into the building enclosure.


Air Barrier Material - A material designed to be the primary air barrier in a building enclosure. Air Barrier materials should be 'Air Impermeable' which is defined as a material that allows less than 0.02 L/s per m2 of air permeance (through) at 75 pascals pressure difference. Drywall is the most common air barrier material in houses. Open and Closed cell spray foam can also be used as a Air Barrier Material.


Air Infiltration - Air leakage into conditioned space. This is natural, unplanned (and generally unwanted) allowance of unconditioned external air into the conditioned internal space.


Air Leakage - See Air infiltration above.


Air Permeable Material - These are structural materials which can be part of the building enclosure but are not intended as part of the air barrier.


ASHRAE - The American Society of Heating, Refrigeration and Air Conditioning Engineers. ASHRAE is an international technical society for all individuals and organizations interested in heating, ventilation, air-conditioning, and refrigeration.


Balloon Framing - A method of building framing where the walls are framed from long continuous wall studs that run from the sill plate to the roof eaves. Floors, windows and other fixtures are built around the continuous framing.


Band Joist - Located between the first and second floors, the vertical lumber element to which the floor joists are attached forming the second floor. This can be a major source of air exfiltration even in modern construction. This is often made worse by leaky supply ducts between the floor joists. The term is also sometimes used in place of Rim Joist (see below).


Basements - The below ground level foundation of a building, often used for storage, utility space, and man caves.


Beam - One of the main structural elements in the building enclosure, traditionally wood though it can be a wide variety of building materials.


Below Grade - In building terms, grade is the ground level. Therefore, below grade…below ground level.


Blower Door - Diagnostic equipment consisting of a calibrated fan, removable panels, and gauges, used to measure and locate air leakage.


Blower Door Test - The blower door depressurizes or pressurizes the house to measure air tightness and identify air leaks. A blower door test can also be run during sealing work so contractors can find areas to be addressed.


Boiler - The core of a water-based heating system. A boiler heats water which is carried through structures via a steam or a hot water distribution system. Steam systems have higher heating requirements (because of the higher operating temperature of steam vs. water). Almost any fuel sources are options but the most common in North America are oil and natural gas boilers.


Borate/Boric Acid - Borates are a class of chemicals added to cellulose as a fire retardant and anti-pest treatment. Borates are created from boron and are also used as treatments for wood and lumber.


Btu - British Thermal Unit - The amount of energy that is required to raise 1 lb. of water up 1° Fahrenheit. Approximately equal to one wooden match.


Btuh - A rate of energy transfer - expressed as Btu/hour


Building Envelope (or Building Enclosure) - The internal elements of walls, floor, ceiling, roof, windows and doors of a building that encloses conditioned space. The Envolope of a building that defines the division between the interior, conditioned space and exterior unconditioned space. Consists of an air, vapor, and thermal barrier.


Building Shell - The external elements walls, floor, ceiling, roof, windows and doors of a building that encloses conditioned space. Can consists of an air, vapor and thermal barrier, a water control plane and the structural elements which include the foundation (or slab), the exterior walls, and roof.


Capillary Action, Capillarity - The directional movement of liquids through a porous material or narrow space (like small cracks), driven by molecular forces. Due to capillary action, liquids can move against gravity or other driving forces. Capillary action occurs because water is sticky, thanks to the forces of cohesion (water molecules like to stay close together) and adhesion (water molecules are attracted and stick to other substances). Adhesion of water to the walls of a vessel will cause an upward force on the liquid at the edges and result in a meniscus which turns upward. The surface tension acts to hold the surface intact. Capillary action occurs when the adhesion to the walls is stronger than the cohesive forces between the liquid molecules. Capillary action (sometimes capillarity, capillary motion, or wicking) is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube, in porous materials such as paper and plaster.


Caulking - One of several types of joint sealant. Refers to a variety of material based caulks (silicon, urethane, or to name a few) today but the term dates back to mixtures of hemp fibers and pine tar used to water seal boats.


Combustible Area Zone (CAZ) - It is the area which houses the appliances that heat the home through combustion, such as a boiler or furnace and water heater. Typically located in the basement, they can also be located in other areas such as garages or portions of the main floors. The CAZ needs to maintain a minimum pressurization to avoid spillage, back drafts, or other hazards.


CAZ Worst Case Depressurization Test - A combustion appliance test evaluating the potential for backdrafting flue gases. We first create the 'worst case depressurization' (activating exhaust fans and closing door to produce the highest negative pressure in the house). We then visually assesses to see if there is any flue gas spillage.


Cellulose Insulation - Cellulose is one of the more common and least expensive forms of insulation. Cellulose is shredded paper typically mixed with boric acid as a flame retardant and anti-pest treatment. Cellulose can be blown loosely over flats, water assisted wall sprayed, or densepacked in wall cavities. Cellulose can achieve approximately R-3.5 to 4.0 per inch depending on the method used.


Chlorofluorocarbon (CFC) - Any of various halocarbon compounds consisting of carbon, hydrogen, chlorine, and fluorine, once used widely as aerosol propellants and refrigerants. Chlorofluorocarbons are believed to cause depletion of the atmospheric ozone layer.


Combustion efficiency - A measure of useful heat extracted from a fuel source by an operating heating appliance. For example a furnace with a combustion efficiency of 60 percent converts 60 percent of the fuels energy content into useful heat. The rest is lost as exhaust gases.


Condensation - When water moves from a vaporous state to liquid. Typically, this occurs when the moist air comes into contact with a surface temperature below the dew point.


Conditioned Space - The space within the building enclosure that is being environmentally controlled.


Conduction - Transmission of heat energy through a material or from one material to another by direct contact. Materials with low rates of conductive heat transfer make good insulation.


Convection - Transmission of heat energy from one place to another by movement of a fluid such as air or water.


CFM - Cubic Feet per Minute. The volume measure for air flow in building science.


CFM50 - This is the airflow (in Cubic Feet per Minute) created by pressurizing a building pressure to 50 Pascals. CFM50 is the most commonly used measure of building airtightness and represents a fictional wind blowing on all sides of the structure at approx. 25 mph.


Density - Determined by weighting a material and finding its volume in cubic feet. After a quick calculation, it is expressed in pounds per cubic foot of the material.


Dew Point - The temperature at which water vapor fully saturates the air (it can't hold any more) and will start to transition to liquid (condense). Solids below the dew point temperature will cause vapor to condense on its surface.


Diffusion - The movement of water vapor from regions of high relative humidity (RH) or pressure toward regions of lower RH driven by a higher to lower temperature differential.


DHW - Domestic Hot Water


Energy Efficiency Ratio (EER) - It is used to measure the efficiency of air conditioners. The EER of a particular cooling device is the ratio of output cooling energy (in BTU) to input electrical energy (in Wh) at a given operating point. EER is generally calculated using a 95 °F outside temp and an inside (actually return air) temp of 80 °F and 50% relative humidity. This is similar to SEER, but it is only done at the single operating condition. ~EER = 0.875 * SEER. More efficient ACs have a higher EER number.


Emissivity - In building science, a material's ability to emit radiation (usually referring to heat and light energy). Emissivity runs from e = 0 (perfect reflection of radiation) to e = 1 . The darker and duller the surface, the closer emissivity will be to 1. Conversely the more shiny/reflective a surface, the closer to 0.


Energy - The ability of one system to exert force over a distance on another system.


Energy Audit - Energy audits are assessments of the insulation, air leakage, and heating systems in your home. Done with the sole focus of reducing the energy consumption of the house. This may result in the house being more comfortable, but usually results in it being far less comfortable.


Energy Recovery Ventilator (ERV) - This is a mechanical system that recovers heat and moisture while exchanging stale inside air for fresher outside air.


Energy Star - Standard for energy efficiency in many consumer products. First developed by the US Dept of Energy, it has since evolved into an international standard for efficiency.


Exfiltration - Uncontrolled air leakage of conditioned air from inside the home to the outside, driven by pressure and temperature.


Expanded Polystyrene (EPS) - This is the white beaded 'styrofoam' most people are familiar with (think Dunkin Donuts coffee cups). It is typically formed into rigid foam boards and has a higher vapor permeability than either XPS or Polyisocyanurate (foil faced). EPS would need to be paired with a vapor barrier in building shell applications.


Facade - The aesthetic and protective exterior of a building.


Faucet Aerator - A mesh screen found at the tip of modern faucets. Rather than coming out in a single stream, the aerator spreads the flow into droplets. This improves flow, reduces splashing and saves water.


Fiberglass Insulation - Fiberglass consists of extremely fine glass fibers. As an insulation, it is cost effective, temperature resistant and equally effective in most climates. The main drawback is that it does not stop air flow in any way. Unless paired with an effective air barrier, fiberglass insulation won't function at the advertised R-value.


Flame Retardant - A substance, which is added to a polymer formulation to reduce or retard the tendency to burn.


Flame Retarded (Adj.) - The property of a material to which flame-retardant has been added.


Flame Spread - Unit of measure generated by a standard test for determining relative combustibility. The flame spread of a tested material is rated relative to red oak (flame spread = 100). ASTM = E84 is the test method used to determine the above.


Flammability - Relative ability of a material to support combustion as expressed by its flash point.


Flashing - A building material for directing exterior water away from the building. Occasionally used in other capacities such air sealing chimney enclosures.


French Drain - An exterior perimeter drain around a building. These drains help reduce basement moisture problems by moving rain water away from the foundation.


Grade - Ground level in relation to the building.


Habitable Space - The space within the building enclosure where folks sleep, dine, cook etc. on a continual basis.

Header - The top structural framing members over all building egresses (primarily windows and doors).


Heat Exchanger - A system which transfers heat from one fluid (gaseous or liquid) to another without mixing the two fluids. Air to air heat exchangers capture a portion of outgoing heat by transferring it to the incoming air flow (this is similar to how forced air furnaces work). Water heat recovery systems do the same for a water medium, capturing some of the potentially wasted outgoing heated water and preheating incoming water.


Heat Gain - The amount of heat gained within a conditioned residential space from non-heating system sources. This includes sunlight, body heat, incandescent lights and the heat radiating from an active boiler/furnace/water heater.


Heating Load - Heating load is the maximum number of BTUs the heating system will need to provide for a comfortable interior temperature. The load is calculated on a near worst case scenario ( typically 1% of the time {totaling 88hrs/year} it is likely to get colder).


Heat loss - Heat that is lost from a building by air leakage, conduction, and radiation. To maintain a steady interior temperature, heat losses must be offset by a combination of heat gains and heat contributed by a heating system.


Heat recovery ventilator (HRV) - A mechanical ventilation system that recovers energy from exhausted indoor air and transfers it to incoming outdoor air. This system usually incorporates an air-to-air heat exchanger which transfers the heat from exhaust air to the incoming air or vice versa (depending on the season).


HVAC - An acronym that stands for Heating, Ventilation, and Air Conditioning. This refers to all of your building's major mechanical systems.


Humidistat - A humidity sensitive control device that signals the ventilation system to operate if the humidity goes above a preset limit.


Hydrochlorofluorocarbons (HCFC) - These are halogeneted compounds containing carbon, hydrogen, chlorine and fluorine. They have shorter atmospheric lifetimes than CFCs and deliver less reactive chlorine to the stratosphere where the "ozone layer" is found.


Hydronic System - Water based system that can provide heating and possibly cooling. It can consist of cast iron radiators, base boards, or in (or under) floor tubing. The system can be a high temperature (radiators and base boards) that provide heat primarily by convection or low temperature (tubing in (or under) the floor that provides heat (or cooling) primarily by radiation.


Hydrophobic - Having no affinity for water; not compatible with water. "Water fearing" Also preventing growth of mold and mildew.


Hygrometer - A tool for measuring the water vapor in the atmosphere. Humidity measurement instruments usually rely on measurements of some additional quantity such as temperature, pressure, mass or a mechanical or electrical change in a substance as moisture is absorbed.


Ice Dam - Ice dams are a lip of ice that forms on the outside edge of a roof. When large enough, water can pool behind the lip, possibly causing roof leaks and water damage. They are formed by an upper portion of the roof being above the freezing point (melting snow) and a lower portion (at the eves typically) of the roof being below freezing.


Indoor air quality (IAQ) - IAQ figures prominently in ensuring sufficient fresh breathable air, reasonable humidity levels and freedom from mold and chemicals.


IECC - International Energy Conservation Code. The international code standard for energy use in construction. In 2012, Maryland other states adopted new energy efficiency code for new construction and retrofits. More testing, including blower door and duct blaster testing is required on new and existing construction.


Infiltration - Uncontrolled leakage of air into a building through cracks such as around doors, windows, electrical outlets and at structural joints. Uncontrolled leakage of conditioned air from outside of the home to the inside.


Infrared Thermometer - A thermometer which uses the infrared spectrum to detect surface temperatures at a distance. This is a useful tool for homeowners to do their own home energy investigations without the much more substantial investment of an infrared camera.


Insulation - Materials with low thermal conductivity characteristics that are used to slow the rate of heat transfer.


Isocyanate (typically MDI) - One of a group of neutral derivatives of primary amines (R-N=C=O) groups. An essential component (A) of polyurethane foam chemistry.


Kilowatt-hour (kWh) Standard unit for measuring electrical energy consumption-kilowatts X hours.


LED bulbs - Light emitting diode. LEDs are extraordinarily long lasting and very efficient compared to either incandescents or CFLs. LEDs produce light with a semiconductor 'filament' instead of the standard metal one.


Low-E Coating - Low E coatings are spectrally selective so as to allow sunlight in but block/reflect a higher degree of solar heat (infrared). Low E or low emissivity coatings are a thin, silvery metal layer on the window pane. Very useful in sunny climates to reduce cooling loads by limiting solar heat gain. In heating climates, it reduces heating by reducing the amount of infrared energy that escapes through windows. Note: Most windows can be set up for heating or cooling, not both. This requires a triple pane with the center pane coated on both sides, but will result in the reduction of solar gain in the winter time.


Low Emissivity - See Low E Coating directly above. We're basically talking about the same thing.


Low Flow Showerhead - Showerhead with less than the 2.5 gpm water flow.


Material Safety Data Sheet (MSDS) - A standard formatted information sheet, prepared by a material manufacturer, describing the potential hazards, some physical properties, and procedures for safe use of a material.


Mold - Fungal growths often resulting in deterioration of organic materials, require moist conditions to grow.


Off Gassing - This is the chemical vapors released from paints, finishes and other materials into the home. This is an indoor air quality issue and must be considered as the building envelope is tightened.


Off Peak Electricity - This is the period of time, usually night, when there is less demand for electricity. Utilities often charge reduced rates for off-peak usage.


On Demand Hot Water - A mechanical system which delivers hot water 'on demand'. This reduces heat loss when there is no hot water useage because the system does not maintain a reservoir of pre-heated water.


Oriented strand board (OSB) - Made by orienting strands of wood slivers and compressing them into a board. OSB use has exploded in the last 30 years, largely supplanting plywood and planed lumber in building shell construction.


Organic - Compounds containing carbon.


Perm - A unit of water vapor transmission defined as 1 grain of water vapor per square foot per hour per inch of mercury pressure difference (1 inch mercury = 0.49 psi).


Pascals - A unit of pressure equivalent to one newton per square meter or 1 psi = ~6900 Pa


Passive Heating - Heating systems for a house that lack a active mechanical component. Usually some variant of solar heating (solar hot air, thermal masses or solar heat gain).


Passive Solar - Utilizing solar in passive manner such as with thermal masses or solar light tubes instead of actively with photovoltaic panels or solar hot water systems.


Permeability - The time rate of water vapor transmission through unit area of a material of unit thickness induced by unit vapor pressure difference between two specific surfaces, under specified temperature and humidity conditions.


pH - A measure of acidity/alkalinity of aqueous mixtures. A measure of pH 7 is neutral, lower is more acidic, higher is more alkaline.


Photovoltaic (PV) - Usually references photochemical cells which generate electric current when under direct sunlight.


Polyisocyanurate (Polyiso) - This is a closed cell solid foam insulation. It usually comes with foil backing. Polyiso can act as an air barrier and has the highest R-value (up to R-7 per inch) of any common insulating material. However, it does not hold up under direct sunlight and does degrade to approximately R-6 after 5-10 years.


Power Vented Exhaust - A combustion system's gas vent that is coupled with a fan system to expedite the removal of flue gases.


Pressurized Fog Testing - Done in conjunction with a blower door test or duct blaster test. Using the blower door, pressurized fog test visually identifies air leaks in a building’s envelope. The test is usually done when temperature and weather conditions make an infrared scan difficult. Using the duct blaster, pressurized fog test visually identifies air leaks in the duct work. The test is usually done during construction to show to the HVAC contractor just how leaky the ducts really are as installed.


Product Data Sheet - A listing of all the general characteristics and components of a chemical or product. (Also see MSDS).


Programmable Thermostat - A thermostat which allows for setting different room temperatures over periods of time. One of the most cost effective ways to reduce your heating or cooling bill.


PSI - Pounds per square inch.


Radiation - Transfer of heat energy from one object to another through an intermediate space without transfering heat to the intermediate space. Thus, only the object receiving the radiation, not the space is heated. The heat is in the form of infrared, (low frequency & invisible) light energy, transferring from a "warm" object to a "cold" object. It is known as the "black body effect".


Relative Humidity - The ratio expressed as a percentage of the amount of moisture air actually contains to the maximum amount it could contain at that temperature.


Renewable Energy - Energy which comes from natural sources such as wind, sun, and hydroelectric. These sources naturally replenish. Compare to non-renewables like coal, natural gas and oil.


R-Value - A unit of measurement of resistance to heat flow in (hr.*ft2*° F)/BTU. Typically, expressed as R-11, R-20, and so on; the higher the number, the greater the resistance to heat flow.


Retrofit - The modification of an existing building or facility to include new systems or components.


Rim Joist - Located atop the foundation wall, the vertical lumber element to which the basement floor joists are attached forming the first floor. This can be a major source of air infiltration even in modern construction.


Sealed Combustion - A means of providing air for heating and hot water appliances where the combustion air and post-combustion flue gases are both piped to the outside. Often done through a concentric vent where both intake and exhaust run in the same pipe.


Seasonal Energy Efficiency Ratio (SEER) - A measure for the energy efficiency of cooling units. The SEER rating is determined by dividing the cooling BTUs produced by the energy used in watt-hours for a typical year period. Unlike the EER's single point, the SEER is thus calculated with the same indoor temperature, but over a range of outside temperatures from 65 °F (18 °C) to 104 °F (40 °C), with a certain specified percentage of time in each of 8 bins spanning 5 °F (2.8 °C). The higher the SEER, the more efficient the cooling unit.


Sheathing - The exterior layer of the building envelope installed over the stud walls. Historically this has been planed lumber boards but in the 20th century this was been supplanted by plywood and later oriented strand board (OSB), but can also be rigid foam boards.


Siding or Cladding - The outer covering of a residence. Provides improved aesthetics and acts as weather protection.


Sill Plate - Located atop the foundation wall, the bottom horizontal lumber to which the basement floor joists are attached. This forms the first floor. The sill plate can be a major source of air infiltration even in modern construction.


Slab On Grade - More commonly known as a slab foundation. A very simple, cost effective alternative to a full basement, slab concrete is poured directly into an excavated mold. Garages, regardless if attached or detached, are often slab on grade construction.


Solar Gain - The energy gained (usually we're talking about heat) from sunlight.


Solar Heat Gain Coefficient (SHGC) - An abbreviation seen on window performance labels. It shows the percent of solar heat allowed through the window.


Spray Foam - A polyurethane-based insulation that is applied via spraying on the insulating surface. The two main types are a denser impermeable closed cell foams and a less dense semi-permeable open cell foam.


Stack Effect - One of the main drivers of air transported heat loss in homes. Warm air naturally drifts upward within the building envelope. This updraft grows stronger as the indoor-outdoor temperature difference grows (the stack draft will be much stronger if outdoor temp is 20 F compared to 50 F and indoors at 70 F). This thermal updraft finds every crack and seam to escape in the building's peak. The updraft also creates a corresponding negative pressure, pulling in cold air at the building's base.


Standard Testing - Laboratory test methodology for determining relative properties of materials or equipment at specific conditions.


Stud - A vertical wood beam used in residential construction of walls.


Sun Tunnel or Solar Tube - A form of passive solar lighting. Solar tubes or sun tunnels are tubes which run from the roof and terminate in a globe which diffuses the light through an interior room.


Superinsulation - The word was coined during the energy crisis of the 70's it is an approach to solving thermal envelope problems. Superinsulation is usually, but not always, one of the several polyurethane foam systems.


Thermostat - "Temperature sensitive" control device that signals a heating or cooling system to operate if the temperature in a conditioned space reaches a preset limit.


Temperature Controls - Temperature controls monitor the heating distribution system's return and supply lines. By examining the difference in temperature between the departing and returning supply, it closely controls the boiler/furnace output.


Therm - 100,000 BTUs. Often used to standardize the comparison of different energy sources. When used for home heating and hot water, natural gas is delivered in therms or deca-therms (1,000,000 btu's).


Thermal Barrier (Thermal Envelope) - The conductive heat control layer (Insulation) of the building envelope.


Thermal Bridge - A thermally conductive material which penetrates or bypasses an insulation system; such as a metal fastener or stud. This results in the movement of heat across a building assembly, often compromising thermal performance of the wall assembly.


Thermal Resistance (R) - An index of a material's resistance to heat flow. See R-Value.


Thermal Shock - A building materials reaction to rapid changes in temperature. This can cause some materials to fail.


Thermography (Infrared Scan, Thermal Imaging) - A building energy diagnostic technique using an infrared camera (a camera that sees the infrared spectrum) for locating areas of temperature differential or air leakage in a building. Often used in conjunction with pressurization or depressurization. They can detect gaps in insulation, air infiltration and water leaks.


Top Plate - The board that forms the top of a wall in platform framed construction.


Unvented - Unvented roofs are those which do not have an active ventilation system. More and more modern construction use unvented roof designs. In cold climates, this requires that the interior air barrier (or other condensing surfaces) stay warmer than the dew point so as to avoid condensation. This makes venting which is intended to transport moisture out of the building unnecessary but requires controlling interior moisture sources.


U-Value - Thermal conductance. U-value is equal to the inverse of the sum of the R-values in a system (U = 1 /R total). Another measure of the thermal resistance (actually thermal conductance) of a building assembly or insulating product, most often used with windows.


Vapor Retarder - A layer of moisture resistant material which controls moisture diffusion to prevent moisture migration into building cavities.
Class I Vapor Retarders (Vapor Barriers or Vapor impermeable) have a permeability of 0.1 perm or less.
Class II Vapor Retarders (Vapor Semi-Impermeable) have a permeability of 1.0 perm or less and greater than 0.1 perm.
Class III Vapor Retarders (Vapor permeable) have a permeability of 10 perm or less and greater than 1.0 perm.


Venting - Most modern residential construction ventilates the roof & occasionally the basement. The main goals with ventilated roofs are controlling roof temperature, extending the life of roof sheathing and, during the winter, slowing the melting of snow. A desired benefit is controlling moisture. A roof ventilation system usually consists of continual venting along the roof edge (known as soffit or edge vents), channel vents running along the roof deck (known as channel or proper vents) leading to either a ridge vent (running the length of the roof peak), several individual vents (turtle vents), or gable end vents.


Volatile Organic Compounds (VOC) - Any compound containing carbon and hydrogen or containing carbon and hydrogen in combination with other elements. VOCs are carbon-based compounds which can evaporate at room temperature. Found in many home products, they can contribute to air quality issues.


Weatherstripping - Material additions to the seams of doors and windows to reduce the leakage of interior conditioned air.


Extruded Polystyrene foam insulation (XPS) - This foam board insulation has advantages in that it is water resistant, can act as an air barrier and has higher insulating values (R-5.5 to R-6.5 per inch) than many other common insulating materials.