ucing repair and maintenance costs.
How do we improve home energy efficiency?
Increasing insulation is perhaps the first answer
that comes to mind, but it is only part of the
answer. Improving our homes energy efficiency
involves an understanding of the thermal enve-
lope, that barrier to heat loss (and summer heat
gain) that protects and separates the indoor living
space from the outdoor climate. (See Figure 1.)
Insulation is the heart of the thermal envelope,
but it is only one part of an entire system that
also includes siding, sheathing, sheetrock, and
other materials that prevent heat loss through air
leaks and keep wind and moisture from penetrat-
ing the thermal envelope, reducing the effective-
ness of the insulation.
Any program to improve home energy efficiency
must pay attention to the entire thermal envelope.
Before insulation is added, two important steps
need to be taken: first, a system for controlling
the intake of air into the home (and venting stale
air out) must be supplied, and second, air leaks in
the thermal envelope should be sealed. See the
Sidebars on Attic Bypasses and Air Ventilation for
information on how to proceed with these impor-
tant steps before increasing insulation.
The role of insulation
Heat naturally flows from a warm to a cool place.
In winter, heat flow is from indoors to outdoors;
in summer, the movement is reversed. Insulation
resists this heat flow, which is why an insulated
home is warmer in winter and cooler in summer.
How well insulation works in resisting heat flow
depends on where and how it is placed and on
what and how much material is used.
Figure 1 shows a home and indicates where insu-
lation would be placed to create a barrier to heat
loss.
The type and amount of material used also affects
how well the insulation works. Insulation material
is rated according to its R-value, or resistance to
heat flow. The higher the R-value the better the
insulation is in reducing heat flow.
Is more insulation needed?
Checking current insulation level. To determine
if you need more insulation, you must first find
out how much insulation you have. One way to
do this is to check for yourself. Look at Figure 1.
You will want to see if you have insulation (and
how much) in these key locations the basement
walls, exterior walls, floors above cold spaces, and
ceilings below cold spaces. In unfinished areas
such as attics, where structural frame elements
are exposed, you can see the type of insulation
and measure its thickness.
Minnesota Department of Commerce
1
Related Guides:
Basement Insulation
Caulking & Weatherstripping
Windows & Doors
Home Heating
Home Cooling
Combustion and Makeup Air
Indoor Ventilation
Attic Bypasses
TECHNIQUES
TACTICS
& TIPS
H O M E
E N E R G Y
G U I D E
H
OME
I
NSULATION
Minnesota Department of Commerce Energy Information Center
A comfortable home warm in winter and cool in summer is a major priority for most
homeowners . . . and they pay for it! Heating and cooling account for approximately 60 to 80
percent of the average Minnesota households energy costs. Yet in most cases, such high costs
are not necessary.












Radiant Barriers:
Do They Work?
Radiant barriers (or
reflective barriers) consist
of a reflective film installed
over the top of attic
insulation in existing homes
or between the roof deck
and rafters in new
construction and are also
promoted for application
below grade beneath
concrete slab floors. They
are frequently sold as an
energy saving product, with
claims of significant
reductions in both heating
and cooling costs.
Radiant barrier materials
must face an open air
space to have any
significant effect, which
means they will not work in
sub-slab applications and
are ineffective when placed
against other materials or
surfaces. Additional
problems with radiant
barriers include possible
condensation or moisture
trapping in the attic
insulation, and the effect of
dust accumulation on the
surface of the film, reducing
the reflectivity.
An Oak Ridge National
Laboratory study concludes
that attic radiant barriers
are
not an effective way to
reduce heating or cooling
loads in Minnesota. Adding
conventional attic insulation
would be a much better
option for saving energy. In
fact, as the attic insulation
level increases, the potential
benefits from a radiant
barrier decrease. Radiant
barriers in Minnesota are
generally not worth the
investment in terms of
energy savings.
Checking insulation in finished walls and areas is
more difficult. One way to check for wall insula-
tion is to look directly into the wall cavity, either
by removing a switchplate or by drilling holes
into outer walls. After turning off the power, you
can remove a switchplate cover and probe the
wall around the electric outlet box with a plastic
crochet hook or other non-metal instrument
and a flashlight. The drawback to this method is
that it is difficult to get an opening large enough
to make an accurate check.
A more reliable check can be made by drilling
holes directly into an outer wall in a closet or
cupboard or other hidden area. Cut a 1- or 1-1/2-
inch hole with a keyhole, reciprocating, or hole
saw, and determine whether there is any insula-
tion and, if so, how much. These holes should be
filled and finished with patching plaster and
touch-up paint.
Dont be concerned that old wall insulation may
have settled into the lower part of the walls. The
insulation level you see, whether at a high or low
section of the wall, should give you an accurate
picture of the insulation level for the entire wall.
Drilling holes in the walls can also reveal any
obstructions in the wall. For instance, some homes
built between 1910 and 1945 have a sheet of tar
paper or other material in the wall cavity to
reduce heat-robbing air convection (air move-
ment) within the walls.
Another type of convection barrier often used in
homes built before 1930 is backplaster, which is
another layer of plaster within the wall cavity.
Backplaster makes insulating walls more difficult,
but it is still worthwhile to do. Discuss your
options with an insulation contractor and call the
Energy Information Center.
If you do not wish to check for insulation your-
self, a second possibility is to have your utility
do an energy audit or evaluation. A number of
utility companies in Minnesota will do energy
audits. Call your utility and ask for an energy
audit.
Another possibility is to have a qualified indepen-
dent energy contractor do an evaluation, possibly
using such technology as infrared thermography
and blower door technology. Such an evaluation is
reliable and provides valuable information about
your home. If you have any questions about
applying these techniques to your house, call the
Energy Information Center.
Evaluating benefit of added insulation. The deci-
sion whether to add insulation will depend on a
number of factors. A better insulated home is
more comfortable and quiet. It will save you
money on utility bills for years to come. And by
using less energy to heat and cool your home, you
reduce the negative impacts on the environment
caused by energy use.
The graph InsulationThe Difference it Makes,
compares the annual heating bills for three ver-
sions of the same home one with limited insula-
tion and the others with improved levels of
insulation. The heating bill for your home may
differ considerably from amounts on the graph,
depending on the size of your home, the type of
heating fuel you use, the insulation levels, furnace
efficiency, etc. The numbers will, however, give
you an idea of the potential energy savings to be
gained by weatherizing your home, depending on
its present insulation level. The costs of various
improvements can help you decide which
improvements to make.
Basement. Insulating the basement is relatively
expensive, but it makes a significant difference in
comfort and energy use and adds to the living
space of the home. A description of the two meth-
ods of insulating a basementexterior and interi-
oris provided in the publication Basement
Insulation, available from the Energy Information
Center. The information in this guide focuses on
attic-ceiling and wall insulation.
Attic/ceiling. If your attic is poorly insulated, you
could save significantly on your heating bill by
insulating to adequate levelsprovided, of course,
you first seal attic bypasses (page 4). Adding attic
insulation is relatively inexpensive; in the exam-
ples accompanying the graph, increasing the R-
value of attic insulation from 6 to 40 costs about
$465 and reduces heat loss by about 14 percent! If
your present attic-ceiling insulation R-value is less
than 30, adding more insulation would be well
worthwhile.
You can figure out your present R-value by noting
the type and amount of insulation you have and
checking it with information on insulation materi-
2
Minnesota Department of Commerce als and their approximate R-values listed in the
Types of Insulation Table.
In unfinished attics, insulation should be put be-
tween the floor joists to seal off living spaces below.
In finished attics with or without dormers, insula-
tion should go between the studs of knee walls,
between the studs and rafters of exterior walls, and
in ceilings with cold spaces above (Figure 1).
In deciding whether to add insulation, you should
check not only the present level of insulation, but
also its condition. Is it level, or are there bare
spots or pi