The following article was written by Laurie L. Dove and can be read in full here… http://home.howstuffworks.com/most-energy-efficient-way-to-insulate-an-attic.htm
When installing mineral wool, use a higher R-value than you think you’ll need to offset the loss that will occur over time.
You feel a cold draft in that one dark hallway upstairs — so who you gonna call? Before you check in with paranormal investigators, check your energy bill. If it’s running high, the solution may be much simpler than a séance: Beefing up the insulation in your attic is one of the easiest ways to make your home more energy efficient.
Before you can select an insulation, however, you’ll need to understand its resistance to heat flow, or R-value. The higher the R-value, the more effective the insulation will be at keeping your house warm in the winter and cool in the summer. If you live in North America, you can find the recommended R-value for homes in your area on the North American Insulation Manufacturer’s Association Web site. Keep in mind that the effect of R-values is cumulative. For example, if your attic has R-19 insulation and another layer of R-19 insulation is added, the insulation will have a value of R-38.
Loose-fill insulation, also known as blown-in insulation, is made of small clumps of recycled materials such as fiberglass, cellulose or mineral wool (which is made of natural mineral or metal remnants). It’s usually installed by professionals who use special equipment to spray it onto the attic floor and into attic wall cavities [source: U.S. Department of Energy]. However, loose-fill insulation, especially that comprised of cellulose, can lose up to 20 percent of its R-value as it settles and compacts over time, so it’s a good idea to install extra to offset the loss.
Batt and roll insulation, also known as blanket insulation, is usually comprised of fiberglass, although some is made of mineral wool, plastic fibers or natural fibers (like cotton). Roll insulation comes in a variety of widths, and its length can be cut to fit during installation. This type of insulation is a relatively simple do-it-yourself project, but it’s important to research local building and fire codes and permits before you start, and to follow the manufacturer’s directions. On average, roll insulation costs less than other types of insulation [source: U.S. Department of Energy].
Installing high R-value insulation in your attic will create a barrier to prevent the heat or cold from escaping, thus making your home more energy efficient. Sometimes, however, insulation isn’t enough. You’ll also need to prevent hot air from leaking out of the attic through unsealed cracks, roof vents, windows or chimneys. These leaks waste energy and can cause structural damage to a home, especially in snow-prone climates. When warm air escapes through an unsealed gap in the attic, it causes the snow and ice on the roof to melt. This continual thawing process can cause moisture to seep into and damage underlying materials [source: Hynek].
These energy-wasting, damage-causing gaps can be sealed with caulking, spray foam, plastic sheeting or weather stripping, each of which has its own benefits and drawbacks [source: Energy Efficiency and Renewable Energy Clearinghouse]. To determine which will be best for you, search the U.S. Department of Energy Web site or talk to an expert at a trusted hardware store or contracting business. Whatever types of insulation you choose to install in your home’s attic, you can expect to pay more for those with higher R-values.