Insulation and Ventilation Terms
Humidity, relative
the amount of water vapor that is actually in the air compared to the amount of water vapor that could exist in the air at a given air temperature, expressed as a percentage. More moisture can exit in warm air than cold air, so raising air temperature while keeping the water vapor constant reduces relative humidity
Vapor Drive?
a condition that occurs when heat vapor pressure cause increase vapor diffusion. One example is when water vapor diffuses through permeable building material from heated interior ares in the winter. Another example is when solar radiation heat wet bricks forcing water vapor though permeable building materials in the summer.
Dew Point (temperature)
the temperuatre at which water vaopr in the air may condense into liquid water. A higher dew point temperature indicates that the air contains more water vapor
Permeability
the ability or proper of material to resist or allow the diffusion of water vapr through said material. Permeability is expresed as a number greater than zero.
R-value
the ability or property of a material to slow heat transfer. A high R-value number equals a higher ability to slow heat transfer. R-value is expressed as a number greater than zero and is used to compare the insulation value of materials
U-value (factor)
the ability or property of a material to allow heat transfer. it is the inverse of R-value and is expressed as a number greater than zero. The larger the number, the higher the rate of heat transfer and a lower R-value
