What's going on in your attic?

Here's what the research says, in plain English.

1. 1

   9 out of 10 homes don't have enough insulation

   About 90% of U.S. single-family homes are under-insulated — wasting energy and money and making homes less comfortable.

   Source: North American Insulation Manufacturers Association (NAIMA), based on the U.S. Energy Information Administration's Residential Energy Consumption Survey. "Under-insulated" means below the minimum levels in the 2006 International Energy Conservation Code.

2. 2

   Sealing and insulating can cut heating and cooling costs about 15%

   The EPA estimates homeowners save an average of 15% on heating and cooling costs (about 11% on total energy costs) by air sealing their homes and adding insulation in attics, floors over crawl spaces and basement rim joists.

   Source: U.S. EPA, ENERGY STAR "Seal and Insulate" program. Savings vary by home and climate.

3. 3

   A hot attic works against your AC

   On a sunny Carolina afternoon, an attic can get far hotter than the air outside. Without good ventilation, that heat soaks down through the ceiling and your air conditioner runs longer to keep up. Balanced ventilation — air coming in low at the soffits and going out high near the ridge — helps move that heat out.

4. 4

   Trapped moisture causes winter problems

   In cold weather, warm, moist air from inside the house can rise into the attic and turn to water on the cold underside of the roof. Over time that can lead to damp insulation, mold and wood rot. Good ventilation and air sealing help keep the attic dry.

5. 5

   Indoor air matters too

   The EPA notes that levels of some pollutants can be two to five times higher indoors than outdoors. Keeping moisture under control — including in the attic — is one way to help prevent mold.

   Source: U.S. EPA, Indoor Air Quality.