The key to a properly insulated building is the selection of an insulating medium that is effective in two ways. The insulating material must keep the building warm in the winter and cool in the summer, at reasonable installation and maintenance cost levels. A wide variety of insulating materials are available to manage the heating and cooling of any building.
Blankets and Batts
The most common building insulation is provided by batts or blankets of expanded fiberglass or rock wool. They are applied after the framing stage of construction and before application of interior wall finishes. Individual batts or roll goods are placed in the spaces between wall studs or ceiling joists and stapled in place. Insulation value of common insulating materials is determined by the "R" value of the material. The R value for fiberglass blankets is 3.3 per installed inch and 3.7 for rock wool, meaning they are good insulators of heat. Well insulated modern homes are designed with R values of 19 for exterior walls and R 34 for ceilings.
Polyurethane Insulating Materials
Expanded polyurethane delivers very good R values, making them possibly the best insulation for exterior walls. The material is available in board form, as a spray-on material, expanded in place or applied in sheets. R values for polyurethane materials range between 5.0 and 7.0 per installed inch. These products are not readily available in all construction markets and are expensive when compared to other insulating materials.
Cork and Wood Fiber Boards
The principal advantages of insulating board installations are reasonable cost and ease of application. Do-it-your-selfers find it easy to apply under the application of gypsum wall board. The material is usually available in 1/2- and 1-inch thicknesses at most home improvement centers. Fiber and cork boards provide insulation of 3.0 per installed inch.
Loose Fill Insulation
Loose fill insulating materials fall at the low end of the cost and efficiency scale. Wood shavings, sawdust and straw have been used as cheap insulators. All of these materials suffer the disadvantages of moisture absorption and low R values, and they provide attractive homes for insects. Typical R values range from 2.0 to 2.5 per installed inch.
For those tempted to eliminate insulating materials from a construction project, the bottom line is air space. Air adds no cost to a project, provides an R value of 1.0 per inch of space and must be completely sealed to prevent air circulation and heat loss or gain.