State University Extension
Home Maintenance And Repair
Energy Tips - Home Insulation Lower your energy costs and
provide creature comfort
and cooling your American home accounts for 50 – 70% of your home
energy use. 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 U.S. is not insulated
to the optimal level. Older homes are likely to use more energy than
newer homes, usually due to inadequate insulation and air leakage.
Insulation saves money. It also makes your home more comfortable by
helping to maintain a uniform temperature through the house.
It is important to:
• Insulate your attic to recommended levels, including the attic door
or hatch cover
• Provide the recommended level of insulation under the floor, above
unheated spaces, around walls in a heated basement or unventilated
crawl space, and on the edges of slabs-on-grade.
• Use the recommended levels of insulation for exterior walls for new
home construction. When remodeling or residing your house, consider
using the levels recommended for new construction in your existing
How Insulation Works
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
through ceilings, walls, and floors – wherever there is a difference in
temperature. During the cooling season, heat flows from outdoors into
the house. See Table 1.
Insulation decreases this heat flow by providing effective
resistance to the flow of heat. Insulation is rated in terms of thermal
resistance called R-values that indicate the resistance to heat flow.
The higher the R-value, the greater the degree of insulating
effectiveness.The R-value of thermal insulation depends on the type of
material, its thickness, and its 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 Rvalue
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 that is
compressed will not give its fullest 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 joints. Therefore, the overall R-value
of a wall with insulation between wood studs is less than the Rvalue of
the insulation itself because the wood provides thermal short-circuits
around the insulation. The short-circuiting through metal framing is
much greater than through wood framed walls.
Does Your Home Need More Insulation?
To begin you must answer this question: find out how much
insulation you already have and then determine how much more would be
cost effective. A qualified home energy auditor will include an
insulation check as a routine part of an energy audit. For information
about home energy audits, call your local utility company.
If you don’t have someone else to inspect your home, you’ll need to
look for insulation in the attic, then check walls and floor adjacent
to an unheated space like garage or basement. In those places, the
structural frame elements (the ceiling joists or wall framing boards)
are often exposed, making it easier to examine the insulation and to
measure depth and thickness of insulation.
It is more difficult to inspect your exterior walls. One method is to
examine an electrical outlet on an exterior wall, but first turn off
the power to the outlet. Then remove the cover plate and shine a
flashlight into the crack around the outlet box. You should be able to
see whether or not insulation is in the wall. In older homes, you may
want to check more than one outlet because wall insulation on one wall
doesn’t necessarily mean that it is everywhere in the house. Next,
inspect and measure the thickness of any insulation in unfinished
basement ceilings and walls or above crawl spaces.
Types of Insulation
Although insulation can be made from a variety of materials, it
usually comes in four types: batts, rolls, loose-fill, and rigid foam
boards. Each type is made to fit in a different part of your house.
Batts are made to fit between the studs in your walls or between the
joists of your ceilings or floors. Batts are usually made of fiberglass
or rock wool. Also, rolls or blankets are usually made of fiberglass
and can be placed over the floor in the attic.
Loose-fill insulation (made of fiberglass, rock wool, or cellulose) is
blown into the attic or walls. Cellulose is usually made from recycled
newsprint treated with fire-retardant chemicals.
Rigid foam boards are made of polyisocyanurate extruded polystyrene
(XPS or blueboard) expanded polystyrene (EPS or bead board) or other
materials. These boards are lightweight, provide structural support,
and generally have an R-value of 4 to 7 per inch. Rigid board
insulation is made for use in confined spaces such as exterior walls,
concrete slabs, and cathedral ceilings. See Table 2.
Attics and Crawl Spaces
The easiest and most cost-effective way to insulate your home is
to add insulation to the attic. To find out if you have enough attic
insulation, measure the thickness of insulation. If there is less than
R-value 22 (7 inches of cellulose) you could probably benefit by adding
more. Michigan Energy Code for new homes requires R-30 for
attics/ceilings and R-13 for walls.
If your attic has ample insulation and your home still feels drafty and
cold in the winter or too warm in the summer, chances are you need to
add insulation to the exterior walls as well. This is a more expensive
measure that usually requires a contractor, but it may be worth the
cost if you live in a very hot or cold climate and it will increase the
You may also need to add insulation to your crawl space. Either the
walls or the floor above the crawl space should be insulated.
Consider factors such as climate, building design, and budget
when selecting insulation R-values for your home.
Recessed light fixtures can be a major source of heat loss, but you
need to be careful how close you place insulation next to a fixture
unless it is marked “I.C.” and is designed for direct insulation
contact. Check your local building codes for recommendations. As
specified on the product packaging, follow the product instructions and
wear the proper protective gear when installing insulation.
Energy Tips - Home Insulation, Michigan State University Extension E2798
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June 30, 1914, in cooperation with the U.S. Department of Agriculture.
Thomas G. Coon, Director, MSU Extension, East Lansing,MI 48824. This
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products or trade names does not imply endorsement by MSU Extension or
bias against those not mentioned.
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