Insulation is the term used for a variety of materials used to reduce heat transfer. It is part of the building envelope, used to limit heat loss through walls, roofs or floors. There's also electrical insulation, which is similar but for electricity.
In most climates the exterior temperature is very different from the desired interior temperature. This is why people heat or cool their homes. These systems require energy to operate so the purpose of insulation is to allow the internal temperature of the building to be as unrelated as possible to the external temperature. If a building is insulated properly, this can result in large energy savings. This is beneficial from an economical, environmental and social point of view.
Because of the large number of insulation types on the market, it is important to have a common rating system. North America uses a unit called the R-value (Resistance value) to measure the performance of an insulation. The Metric unit for thermal resistivity is the RSI. The R-value measures the material's resistance to thermal conduction. It is important to note that heat transfer occurs through three different mechanism; conduction, convection and radiation. A limitation of the R-value is that it only accounts for conduction. This can result in a slightly inaccurate representation of the true resistance to thermal transfer of a material. R-values, however, are a simple way to compare materials' insulating qualities
The R-value is found using the following formula:
The SI units of an R-value are m2·K/W
Since the R-value is inversely proportional to the heat transfer through the object, the higher the R-value, the better the insulator. That is, the greater the R-value, the greater the resistance to heat transfer. A typical 2"x4" wall assembly, insulated with fibreglass batt insulation, will have and R-value of about 13.73. Fibreglass insulation is one of the most common types of insulation in walls. The R-value is reduced to 2.73 when the insulation is removed. R-values can be added normally. So if two materials are together the total R-value is just the R value of one plus the R-value of the other.
Below is a table of R-values.
|Material||R-value per inch||Insulation||R-value per inch|
|Drywall||0.90||Fibreglass Batts||3.0 - 3.8|
|Hardwood||0.90||Cellulose||2.8 - 3.7|
|Sand and Gravel||0.09||Rigid Board - Extruded Polystyrene||5.0 - 6.3|
|Cement Mortar||0.20||Spray-Foam Polyurethane||5.6 - 6.2|
|Brick||0.20||Vacuum Insulated Panels||39|