Let the Sun In
At the start of spring, most people are ecstatic to see the sun's rays pushing the colder days of winter away. But as the spring drags on into summer just about everyone finds themselves wishing for cooler weather. In properly insulated homes the unique discomforts each season brings is considerably less of a bother. Proper insulation has come even more into focus over the last fifty years because of the steady rise of energy costs. The investment of properly insulating a structure will quickly pay for itself, continue reducing energy costs and provide a multitude of benefits that come with a comfortable ambient temperature. Below are some insulation basics to help consumers better understand insulation terminology and principles.
Insulation is a building material that absorbs or reflects the exchange of heat between the interior of a structure to outside. Heat can be exchanged three ways; Conduction, Radiation and Convection. Heat is transferred by Conduction when elevated temperatures are exchanged from two objects in direct contact. Heat is transferred by Radiation when elevated temperatures are exchanged from two objects that are not directly touching through rays of light (direct or indirect sunlight). Heat is transferred by Convection when elevated temperatures are exchanged by circulation within a given space (heat rising). Various forms and applications of insulation are better at maintaining ambient temperatures and reducing energy costs.
For North American consumers the most often seen value concerning thermal insulation's effectiveness is a measure known as R-Value. R-Value is the value given to specify a materials resistance to conductive heat. The higher the stated R-Value the better the material will block conductive heat. Fibrous or cellular material insulations typically resist conduction. For International consumers the most standard value seen as a measure of an insulation's effectiveness is the U-Value. The U-Value is a much broader measure of insulation's ability to resist heat transfer because it takes into account all three methods of heat transfer (Conduction, Radiation and Convection). Unlike R-Value, a lower U-Value shows that the material or product is more efficient at resisting heat transfer. E-Value is primarily related to reflective insulation or radiant barriers. E-Value is the measure of a material or products ability to resist heat transfer by radiation (radiant heat). A higher E-Value indicates that a material or product is more efficient at resisting radiant heat.
In order to best ascertain what product is best for a certain application the methods of heat transfer need to be considered heat-loss-diagram Once the methods of heat transfer are identified different product heat transfer resistance values can be used to determine which insulation will work best for that specific application. For example, in an attic heat is transferred primarily by conduction and radiation. A product with only the R-Value listed, as is common with most traditional insulation, may provide an effective means of preventing heat transfer via conduction but it does not address the heat transfer via radiation that is often excessive in most attics. Similarly, a product that only lists the E-Value may be an efficient means of preventing heat transfer via radiation but determining how well it will resist heat transfer via conduction is unclear because of the absence of a R-Value. Products only listing an E-Value are sometimes seen in radiant or reflective barriers. The effectiveness of products listing only a U-Value for certain applications are more difficult because all three methods of heat transfer are taken into account. It should also be noted, that many times materials or products are used in conjunction. For example, a radiant barrier with a high E-Value used in conjunction with a high R-Value cellulose insulation would likely prevent heat transfer in an attic if installed properly. Similarly, a product that combines a reflective membrane and insulation, commonly seen in reflective insulation, may provide equal or greater results, for an attic application.