Why we insulate
Electricity bills, oil bills, gas bills--all homeowners pay for one or more of these utilities,
and wish they paid less. Often many of us do not really know how to control or reduce our utility
bills. We resign ourselves to high bills because we think that is the price we have to pay for a
comfortable home. We encourage our children to turn off the lights and appliances, but may not
recognize the benefits of insulating the attic.
Heating and cooling ("space conditioning") account for 50 to 70% of the energy used in the average
American home. About 20% goes for heating water. On the other hand, lighting and appliances and everything
else account for only 10 to 30% of the energy used in most residences. It makes good sense to turn lights and
appliances off when they are not needed, and you'll save even more on your energy costs if your reduce the amount
of energy needed for heating and cooling.
Unless your home was constructed with special attention to energy efficiency, adding insulation will probably
reduce your utility bills. Much of the existing housing stock in the United States is not insulated to the best level.
Older homes are likely to use more energy than newer homes, leading to very high heating and air-conditioning bills. Even
if you own a new home, adding insulation may save enough money in reduced utility bills to pay for itself within a few years,
continue to save you money for as long as you own the home, and increase the resale value of your house.
The Crucial Role of Thermal Insulation
Inadequate insulation and air leakage are leading causes of energy waste in most homes. Insulation saves money and
our nation's limited energy resources. It can also make your house more comfortable by helping to maintain a uniform
temperature throughout the house. Walls, ceilings, and floors will be warmer in the winter and cooler in the summer.
Insulation can also act as a sound absorber or barrier, keeping noise levels down.
It is possible to add insulation to almost any house. You may be able to do the job yourself if the structural framing
is accessible--for instance, in unfinished attics or under the floor over an unheated space. Or, you may prefer to hire
an insulation contractor. In either case, it is important to choose and install the insulation correctly.
The amount of energy you conserve will depend on several factors: your local climate; the size, shape, and construction
of your house; the living habits of your family; the type and efficiency of the heating and cooling systems; and the fuel
you use. Once the energy savings have paid for the installation cost, energy conserved is money saved--and the annual
savings will increase if utility rates go up.
BLOWN-IN loose-fill insulation includes loose fibers or fiber pellets that are blown into building cavities or attics
using special pneumatic equipment. Another form includes fibers that are co-sprayed with an adhesive to make them
resistant to settling. The blown-in material can provide additional resistance to air infiltration if the insulation
is sufficiently dense.
BLANKETS, in the form of batts or rolls, are flexible products made from mineral fibers. They are available in widths
suited to standard spacings of wall studs and attic or floor joists. Continuous rolls can be hand-cut and trimmed to fit.
They are available with or without vapor retarder facings. Batts with a special flame-resistant facing are available in
various widths for basement walls where the insulation will be left exposed
How Does Insulation Work for You?
Heat flows naturally from a warmer to a cooler space. In the winter, this heat flow moves directly from all heated
living spaces to adjacent unheated attics, garages, and basements, or to the outdoors; or indirectly through interior
ceilings, walls, and floors--wherever there is a difference in temperature. During the cooling season, heat flows from
outdoors to the house interior. To maintain comfort, the heat lost in winter must be replaced by your heating system and
the heat gained in summer must be removed by your air conditioner. Insulating ceilings, walls, and floors decreases this
heat flow by providing an effective resistance to the flow of heat.
Insulation is rated in terms of thermal resistance, called R-value, which indicates the resistance to heat flow. The higher
the R-value, the greater the insulating effectiveness. The R-value of thermal insulation depends on the type of material,
its thickness, and density. In calculating the R-value of a multi-layered installation, the R-values of the individual layers
are added. Installing more insulation in your home increases R-value and the resistance to heat flow.
The effectiveness of an insulated wall or ceiling also depends on how and where the insulation is installed. For example,
insulation which is compressed will not give you its full rated R-value. Also, the overall R-value of a wall or ceiling
will be somewhat different from the R-value of the insulation itself because some heat flows around the insulation through
the studs and joists. That is, the overall R-value of a wall with insulation between wood studs is less than the R-value
of the insulation itself because the wood provides a thermal short-circuit around the insulation. The short-circuiting
through metal framing is much greater than that through wood-framed walls; sometimes the metal wall's overall R-value
can be as low as half the insulation's R-value. With careful design, this short-circuiting can be reduced. More information
can be found on the Web about whole-wall R-values.