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Air Barrier:

A semi-impermeable layer placed on the building enclosure to control the movement of air into and out of the building.  

Air Exchange Rate:

Number of instances (per hour) of 100% replacement of air contained within the building enclosure by outside air. Usually measured by means of blower door testing.  


American Society of Heating, Refrigerating and Air-Conditioning Engineers

Building Enclosure (Building Envelope, Building Shell):

The layer of wall, floor, and roof components in a building that separate interior spaces from the outside environment. Includes all structural and thermal control elements.  

Conductive Heat Transfer:

The transfer of thermal energy directly through a building material, from a region of high temperature to an area of low temperature. The continuous, unbroken, and relatively high values of insulation left in place by Fox Blocks ICFs prevent "thermal bridging" in clear and undisturbed areas of ICF wall. This supports the thermal control capacity of the building as a whole, and reduces the "appetite for energy".  

Convective Heat Transfer/Thermal Convection:

Convective heat transfer, or convection, is the transfer of heat from one place to another by the movement of fluids, like air or water. Examples are found in air leakage around doors and windows or heat rising through open areas of multi-story buildings (buoyancy). Convective heat transfer (clear wall areas)is dramatically reduced in ICF buildings due to the air-impermeable layer of concrete that forms the core and structure of the building. A recent Canadian study attributes a 60% reduction in total air leakage to ICF construction.

Energy Modeling:

A computer driven simulation of the thermal performance of a building over the span of a year, using different variables for characteristics like building orientation, insulation levels, amount of air infiltration through the building enclosure, and more. Used for cost/benefit analysis of building materials and methods.  

Energy Recovery Ventilators (ERV):

An energy recovery ventilator (ERV) is a type of mechanical equipment that features a heat exchanger combined with a ventilation system for providing controlled ventilation into a building. The benefit of using energy recovery is the ability to meet the ASHRAE ventilation & energy standards, while improving indoor air quality and reducing total HVAC equipment capacity.

Heat Island Effect: 

According to the U.S. Environmental Protection Agency (USEPA), “The term "heat island" describes built up areas that are hotter than nearby rural areas. The annual mean air temperature of a city with 1 million people or more can be 1.8–5.4°F (1–3°C) warmer than its surroundings. In the evening, the difference can be as high as 22°F (12°C). Heat islands can affect communities by increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, heat-related illness and mortality, and water quality.

Indoor Air Quality (IAQ):

This term refers to the comfort and safety levels experienced by the occupants of the building, as a result of the conditioning and handling of air supplies within the building shell. Features like constant air temperature and low levels of particulates (dust, mold, pollen, or pollutants) are seen as desirable conditions in occupied spaces. Uncontrolled air leakage in the building shell may lower the Indoor Air Quality.  

Moisture Barrier:

A layer of plastic or foil which resists the diffusion of moisture through wood and steel cavity wall, ceiling, and floor assemblies. 

Net Zero Energy:

A popular term used to describe buildings that demonstrate a balance between energy consumption and production over the span of a year, or a "net-zero" rate of consumption of energy produced for the public grid.

Passive Solar Design:

According to the US Department of Energy, “Passive solar design takes advantage of a building's site, climate, and materials to minimize energy use. A well-designed passive solar home first reduces heating and cooling loads through energy-efficiency strategies and then meets those reduced loads in whole or part with solar energy.”

Prescriptive Design:

Standardized construction specifications (both structural and energy related) contained in local and national building codes that can be included in building plans without review by a licensed engineer. Used to gain plan approval in buildings that fall within certain size and story parameters spelled out in the code. (Mostly residential)


R-Value is a measure of thermal resistance, or how well a building material is likely to resist heat flow. A higher R-value means lower heat loss. R-value is the reciprocal of U-value.  

Thermal Bridge:

A pathway for heat; Any point at which a high rate of unwanted heat flow can occur across the building enclosure cross-section. Examples are found in uninsulated posts, studs, and headers in wood buildings, and exposed exterior concrete building elements that are also exposed to interior conditioned space.  

Thermal Enclosure (Thermal Shell, Insulating Layer):

Elements in the building enclosure that are dedicated to control of heat flow through the plane of the building enclosure. Usually excludes structural elements, unless they are part of the thermal control system, like ICF and SIP walls.  

Thermal Mass:

Thermal mass is the ability of a material to absorb and store heat energy. A lot of heat energy is required to change the temperature of high density materials like concrete, bricks and tiles. They are therefore said to have high thermal mass. Lightweight materials such as timber have low thermal mass. Appropriate use of thermal mass throughout your home can make a big difference to comfort and heating and cooling bills.