According to the US Department of Energy, insulation is one of the most cost-effective ways of increasing your whole-house energy efficiency and decreasing your energy costs. Unless you are remodeling or building on an addition, this normally means checking on (and probably improving) the insulation in your attic. Insulation in the walls and, in some cases, floor of your house are an important part of your energy picture, but changing them after construction can be a time-consuming and expensive project, so this article will concentrate on attic insulation.
There are several different types of insulation available for attic installation, but in most cases, the easiest (but not only) solution is to add more of whatever type you already have. There is one obvious exception to this: if you have any reason to believe you might have asbestos insulation, make sure you consult with a licensed contractor! You can add loose fill insulation over fiberglass batt insulation, but if you decide to add batt insulation over loose fill, make sure there is no paper or foil backing on the fiberglass batt.
How much insulation should you have? Well, according to the Energy Star program website,most attics should have an R value of 38. The http://www.energysavers.gov website recommends attic insulation values up to R-60, depending on where in the country you are located. ForR-38, if you're using loose fill insulation, this should work out to an even application of approximately 12 to 14 inches throughout the attic, all the way to the corners.
How much does insulation cost? Prices vary widely between different types of insulation and their associated labor charges if you pay someone else to do the work, but generally speaking, loose fill insulation is the least expensive option. A quick Internet search shows estimated pricing around $0.02/R-value/square foot, so an R-38 installation would be $0.76/square foot.
The last major insulation type that we haven't discussed is spray-in-place insulation. This type of insulation is sprayed on and quickly expands to fill all available cracks and is an excellent thermal and air barrier. There are several different kinds of spray-in-place insulation available to choose from, but the most common appear to be either soy or petroleum based polyurethane spray foam insulation.
This is by no means an exhaustive article on attic insulation, but it should give you a good start. There are many different competing products available made from many different materials, all of which have their own positives and negatives. Please research thoroughly before making any major purchasing decisions.