Attic or Ceiling Insulation


One of the easiest and most cost-effective energy improvements you can make to your home is to increase the amount of insulation in your attic. A poorly insulated attic wastes your energy dollars in both winter and summer. In cold weather, a large percentage of the home's heat loss occurs through the attic, and in summer the attic is one of the greatest sources of heat gain. Insulation resists the flow of heat in either direction, helping you save energy costs for both space heating and air conditioning.

Unlike exterior walls, which are enclosed and have limited space for insulation, attics are usually accessible and have plenty of room for additional insulation. Assuming this is the case, there are several options for increasing insulation.

Materials


The two most common insulation materials used in attics are fiberglass and cellulose. Fiberglass can be purchased in the form of batts/blankets or loose fill. The batts or blankets can be rolled out and cut to the appropriate length and are usually the easiest material for a homeowner to install. Loose fiberglass is typically installed using an insulation-blowing machine, usually by a professional insulation contractor. Some suppliers will also rent insulation blowing machines for do-it-yourself installation. Cellulose insulation is another type of loose-fill insulation, made from recycled newspaper or wood fiber that has been treated to make it fireproof. Either material works well as long as you install enough to achieve the recommended R-value.

R-value (which represents resistance) is the standard measure of insulation effectiveness. The higher the R-value, the better the insulation resists the flow of heat. You should have a minimum of R-30 if possible, and in colder climates even more. The table below shows U.S. Department of Energy recommendations for attic/ceiling R-values based on climate. These recommended levels have been determined to be cost-effective for most homes.

Climate Recommended R-value
Warm with cooling and minimal heating requirements R-22 to R-38
Mixed with moderate heating and cooling requirements R-38
Cold R-38 to R-49

Preliminary Steps


The first step is to determine how much insulation you currently have. To do this you'll need to identify the type of existing insulation and then measure the depth. Fiberglass can either be pink, yellow or white, while cellulose is usually grey (it looks like lint) or tan (like sawdust). Once you've identified the material and measured the depth, you can estimate the existing R-value - just multiply the inches by the appropriate R-value per inch.

Fiberglass batts 3.0 - 3.4
Loose fiberglass 2.2 - 2.5
Cellulose 3.7

Once you've estimated the existing R-value, you can decide how much additional insulation to install. Keep in mind that adding insulation has a diminishing return. The more you currently have, the longer it will take for the energy savings to offset the cost of adding more.

Before installing additional insulation, be sure to check for any problems that might be aggravated (or simply hidden) by the new insulation.

  • Check for any signs of moisture problems (stains, mold or fungus growth, rotted wood). Any moisture problems must be corrected before installing more insulation.
  • Make sure to provide clearance around any heat-producing devices like older recessed light fixtures (or replace the bulbs with compact fluorescents that don't generate much heat).
  • Look for any bathroom vents that exhaust into the attic and make sure they're not covered by the insulation. Better yet, use flexible tubing (like for a clothes dryer vent) to direct the exhaust to the closest soffit or eave vent.
  • If the home is very old and has "knob and tube" wiring, you'll need to get a licensed electrician to certify that it is safe to add more insulation.
  • If you're installing the insulation yourself, be sure to identify any soffit or eave vents and install some type of blocking to keep them from being obstructed by the insulation.

Attic Ventilation


Adequate ventilation is important in both summer and winter. In hot weather, it can help exhaust some of the excess heat from the attic, making the insulation more effective. In winter, it can help exhaust any moisture that might otherwise condense on cold surfaces and cause long-term damage.

A qualified insulation contractor should be able to calculate the appropriate number and size of vents based on square footage, type and location of existing vents, and other factors. Options include roof vents, gable-end louvers, soffit or eave vents or ridge vents. In most cases you should have one square foot of vent opening for each 150 square feet of attic area, and the total vent area should be split between high and low vents to ensure balanced air circulation.

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