Grab a tape measure and a flashlight to see what kind of insulation you already have in the attic and how deep it is. Then use the numbers in the chart at right to estimate its R-value. Pull up and dispose of any material that's compressed, water stained, or moldy—it's useless. Owners of houses built before 1990 take note: If what you see is lightweight, grainy, loose-looking insulation with shiny flecks, it could be vermiculite from a mine with asbestos deposits. Get it tested, and if necessary, call in a pro to remove and haul it away safely.