How Does Insulation Work?

Heating and cooling your home represents almost half of the money you will spend on energy every year. If your home is poorly insulated, those costs can be even greater. The amount of insulation as well as its effectiveness is key to your energy use. By nature, heat flows from a warmer area to a cooler area due to the difference in temperature. So in winter, the warm air in your heated rooms will move to the cooler, unheated areas such as the attic, garage, crawl spaces, or outside. During summer, the warm outside air will transfer to the cooler interior of your home because of the higher temperature outside as well as the admission of sunlight. In either case, your HVAC system must work to replace or remove the heat lost or gained. The effectiveness of your insulation will directly impact how hard your HVAC system must work which then directly impact your energy costs. Insulation's role is to slow down the transfer of heat. This is measured in its ability to resist air flow, which is called R-value. The higher the R-value is, the greater its resistance to heat. Its R-value will be determined by the type of material it is made from, the thickness of the insulation and the density of the insulating material itself. There isn't just one correct R-value for all areas of the country or all areas of a house. Shown below is a table prepared by the U.S. Department of Energy for Targeted Insulation Levels for different areas of the country and locations within your home. Target Insulation Levels

If you want to know what the R-value of the insulation in your current home is, either look for an "energy label" containing the home's R-values near the main electric service panel or near the hatch or stairway. If you can't find a posted energy label, look directly on the insulation for the R-value or measure the actual thickness of the insulation. In addition to the R-Value, installing your insulation correctly is critical to its effectiveness. There are five common installation problems that can occur:

1. One of the types of insulation is Batts. If it is compressed, it will provide less resistance to heat and can provide a channel for air and heat movement.

2. If your Batts or Vapor Barrier is stapled to the inside of the studs, unwanted air movement can occur between the studs and the insulation. It should always be stapled on top of the studs, allowing the Batt to completely fill the cavity in which it is placed.

3. Not completely filling irregular areas or small voids with insulation can cause heat loss. A void of 1-2 percent can result in a 25-40 percent loss in R-value in that area. It is for this reason; different types of insulation may be used in the same home.

4. If you don't install loose-fill cellulose insulation to its property density, heat loss can occur. The proper density is called fluffing.

5. Heat can be conducted through the studs and joists of your home. This is called short circuiting or bridging the insulation. With careful design and proper installation, this can be minimized.

While your contractor will be looking out for these common problems, it is helpful for you to know what will be affecting your energy costs for the life of your home. Some areas of your home will have a greater opportunity for heat loss than others. If you have to prioritize which to insulate first, this is the recommended order:

• Attic, including the attic door or cover hatch
• Beneath floors above unheated spaces such as garages, unfinished basements and crawlspaces
• Around walls in an heated basement or unventilated crawlspace
• Around the edges of a slab-on-grade foundation.

As you work with your architect or designer and contractor, ask questions about how your home will be insulated. This planning can save you money in the future as well as protect the earth's precious resources.