Tips on Increasing Attic-Insulation Efficiency
Laying an attic blanket across the joists increases the R-value of the insulation in the attic significantly.
Statistics show that 85 percent of a house's heat loss is straight up through the attic space. Houses built before the energy crunch in the early '70s, might just have a little bit of fiberglass insulation in the attic or empty cavities between the joists. Either way, the house is probably wasting energy – and the homeowners' money.
The amount of insulation a material provides is measured by its R-value. The higher the number in the R-value, the more effective the insulation is. Houses built before the 1970s probably have an R-value of 11 or less, but today's standards call for R-values as high as 38 or more, depending on the house's location.
Some houses may have gray material between the ceiling joists. If it's an old house, that could be mineral wool. A newer house is likely to have blown-in cellulose. Either way, it can be left in place and insulation added over it.
When working with insulation, wear gloves, eye protection and a good particle mask, especially when using fiberglass.
In some ways, rigid foam insulation is easier to work with, but fiberglass is usually easier to get up into the attic.
Don't worry if the fiberglass batt insulation at the home center seems to be too thin. It will expand to as much as 6 inches thick.
To cut a batt to size, lay it on a piece of plywood. Then put a short length of 2x4 at the point where you want to cut, put your foot on the 2x4 and lean on it to compress the fiberglass. Once it's compressed, it's easy to cut with a utility knife.
If you already have six inches of insulation and you want to get to the recommended R-38, add an "attic blanket." It's also made of fiberglass, but it has no paper backing. To install it, just lay it across the joists. Keep adding layers until you get to R-38.
Look for the new no-itch poly-wrap insulation. It is much easier to work with and it's safer, so it's worth the extra cost.