Cellulose insulation and the process of weatherizing and insulating a building involves a number of technical terms and concepts. We've compiled this glossary to help you decipher them.
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Thermal bridging
Thermal envelope
Thermal Radiation or Radiation
Thermography
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Thermal bridging
A thermal bridge is a component or series of components (an assembly) in a building envelope through which heat transfers at a substantially greater rate than the surrounding area. Another way to picture a thermal bridge is as a chain of low-R-Value materials that provide a direct path from the exterior of a building to the interior, uninterrupted by any air space or traditional insulating material.
For example, the assembly consisting of interior drywall, the stud that it is in contact with, the sheathing that contacts the stud, and the siding that contacts the sheathing, represents a direct thermal 'bridge' from the exterior to the interior of a structure. Because these materials have substantially lower R-Values, or resistance to heat conduction, than cellulose insulation, they represent a 'faster" or 'more direct' path for heat to exit the building in winter or enter it in summer.
For example, the assembly consisting of interior drywall, the stud that it is in contact with, the sheathing that contacts the stud, and the siding that contacts the sheathing, represents a direct thermal 'bridge' from the exterior to the interior of a structure. Because these materials have substantially lower R-Values, or resistance to heat conduction, than cellulose insulation, they represent a 'faster" or 'more direct' path for heat to exit the building in winter or enter it in summer.
Thermal envelope
The thermal envelope of a structure consists of the structure's foundation, walls, roof, windows, and doors, considered as a system. The thermal envelope of a structure controls the flow of energy between the interior and exterior of that structure.
Thermal Radiation or Radiation
Thermal radiation is one of the four ways by which heat moves through a structure. Thermal radiation is electromagnetic radiation emitted from the surface of an object, due to the object's temperature. Infrared radiation from a household radiator or electric heater, or the light emitted from a typical incandescent light bulb, are common examples of thermal radiation. Thermal radiation is one of the four ways heat moves through a structure. (See also air infiltration, convection and conduction)
Thermography
Thermography, relative to assessing the insulation and/or air leakage in a structure, measures surface temperatures through the use of an infrared still camera. These cameras see light, invisible to the naked eye, in the heat spectrum. The images record the temperature variations of the building's surfaces, where white typically indicates warmer regions and black indicates colder areas. These images are useful in determining the need for air sealing and insulation, 'before and after' assessments, isolating air leakage from moisture leakage, etc.
