Insulation R-values are numerical values that indicate the level of thermal resistance in insulation. Thermal resistance is the ability of a material to reduce the heat loss of a wall. In the building and construction industry, the insulation R-value is a measure of the effectiveness of insulation products.
The insulation R-value of a material is determined under very specific test conditions, designed to mimic the standard home. Insulation is used to stop the loss of heat through convection, conduction and radiation. In homes and buildings, most of the air in a room is lost through natural convection to the outside.
Insulation works as a barrier to heat loss by acting just like trapped air. The insulation fills up the space between the outer wall and the inner walls of a room. The higher the insulation R-value, the closer it is to the thermal conductivity of trapped air. Air cannot move through air, and so the insulation eliminates heat loss through natural convection by forming an insulation barrier.
Insulation R-values are measured in K·m²/W or kelvin meters squared per watt. As a rule of thumb, the greater the value, the greater the level of insulation provided. The purpose of insulation values is to provide homeowners and consumes one comparable value to assist in the decision making process.
The highest insulation R-values are for Vacuum insulated panels at R-45. Flat, aerogel has a rating of R-10, with isocyanurate foam at R-8.3 and phenolic foam at R-7. Fiberglass blown or loose cellulose both have insulation R-values of R-3.
In the US, there were many cases of deceptive advertising claims on insulation R-values. In response to this the Federal Trade Commission (FTC) issued the R-Value Rule to stop industry wide unfair or deceptive acts. A insulation R-values fact sheet must be provided to customers before the product is purchased and the insulation R-values of the product must be clearly listed on the product label.
Insulation R-values are calculated based on a specific product thickness. Doubling the thickness does not necessarily increase the effectiveness of the insulation and may in fact have the opposite effect. For this reason, insulation R-values are used instead of inches.
The heat loss value of a wall must take into consideration the losses due to windows, wall studs and other conduits through the wall. All of these factors impact on the heat loss of a wall. To maintain a consistently low heat loss values, investigate the insulation R-value of the windows installed in the room.