How Much Insulation Should Be in an Attic?
- To decide how much insulation you need, you must understand R-value in relation to insulation. R-value, as defined by HGTV.com, is "the measurement of the insulation's resistance to heat change." In general, a higher R-value number yields a better insulation. This Old House online suggests that the climate zone you live in will affect what level R-value you use and ultimately how much insulation you will need. Warm weather zones, for example, may need R-38 insulation, but cold weather zones require a higher number, like R-49. Whether heating or cooling, the goal of insulation is to reduce the air flow and thus keep cool or warm air from escaping.
- Next you need to determine how much you currently have and how much more you need. One way to go about this is to hire a professional for an energy audit. A recommendation can be made for how much more insulation you need and where to put it, which you can implement yourself or hire someone to do for you. If you want to get an idea of how much attic insulation is adequate, however, Energy Star (a joint program of the U.S. Department of Energy and the Environmental Protection Agency) suggests that you just take a look across your attic. If you can see the floor joists, you probably don't have enough. If your insulation covers the joists, adding more may not help you conserve energy or save money. Sometimes shifting the insulation and distributing it more evenly will help more than adding extra insulation, Energy Star indicates.
- HGTV.com suggests that homes with an attic insulation depth of 8 inches or less should be supplemented with plastic-wrapped fiberglass insulation or an attic blanket. Ten to 14 inches of insulation is the Energy Star recommendation, depending on the type of insulation you are dealing with. This Old House reminds do-it-yourself installers to wear protective clothing and gear when working with insulation, and be sure you use unfaced batts if adding additional insulation over what you currently have, as the paper or foil barrier could trap moisture in your ceiling. Do not cover can lighting fixtures in the floor unless they are designed for insulation contact. Finally, if you decide to add blown insulation, remember that professional equipment is calibrated to blow the material at a certain density to achieve the highest R-value possible.