Residential Insulation

All of us pay to heat and cool our homes and wish
we could pay much less than we do. In a typical
home, space conditioning and comfort bills can
account for up to one-half of a home's energy bills
with the remaining portion due primarily to water
heating, lighting, and appliances.

Installation of the cost-effective level of insulation is
extremely important. Homeowners can affect their
energy usage, save money, and help the environment
all at the same time. Investing in energy-efficient
options, such as insulation, will provide a continued
payback to the homeowner, not only in dollars and
cents, but also in a more enjoyable and comfortable
living environment for many years, as well as a
reduction in emission of greenhouse gases.

The following are the purposes of this fact sheet:

1. Explain how insulation works,
2. Assist homeowners and new home buyers in

determining the correct level of insulation for
their homes,

3. Present different types and uses of commercially

available insulation, and

4. Explain where insulation should be applied in

the home.

Heat naturally flows from a warmer area to a cooler
one due to a difference in temperature. The greatest
heat flow is through the path of least resistance. In
the wintertime, any heated space of your home will
lose heat to unheated areas such as the garage, attic,
crawlspaces, or the outside. In the summertime, heat
is transferred to the interior of your home due to a
high outside temperature and admission of solar
radiation (sunlight). In both cases, your home's
heating and cooling system must replace or remove
heat lost or gained. Proper insulation of the attic,
walls, floors, and basement of your home will signifi-
cantly help reduce heat transfer, reducing your
monthly energy bills.

All forms of insulation are rated by an R-factor
which is defined as its resistance to heat flow. The
higher the R-factor, the greater the resistance to heat
flow. The R-factor of thermal insulation depends
upon the type of material used and its thickness and
density. Adding additional insulation to your home
increases the R-value and hence the resistance to heat
flow, because the R-values of individual layers are
added together. Two layers of insulation, one with
an R-value of 19 and another with an R-value of 11,
sum to a total R-value of 30 (19+11).

However, a greater level of insulation does not auto-
matically insure cost-effectiveness. Energy savings
associated with installing an additional layer of insu-
lation may not be enough to pay for adding it. The
amount of energy conserved, and hence money saved
due to a greater level of insulation, will depend upon
local climate conditions and the size, shape, con-

Residential
Insulation

Engineering Extension

January 2000

Introduction

Purpose of this fact sheet

How does insulation work?

struction, and orientation of your home. In addi-
tion, the type and efficiency of your heating and
cooling system and fuel costs play an important role.
Other energy efficiency measures such as installation
of energy-efficient windows and periodic mainte-
nance of the furnace and air-conditioning system
also affect overall savings. Each situation must be
evaluated separately to determine cost-effectiveness
of installing additional insulation.

Installation is highly critical with insulation.
Installing the proper level of insulation in your home
does not insure the insulation will stop heat loss if it
is installed incorrectly. The following are some of the
most common insulation installation problems:
1. Compression of batts--insulation that is com-

pressed will provide less thermal resistance than its
rated value and can provide a channel for convec-
tive air and heat movement.

2. Batts or vapor barrier stapled to the inside of

studs--this can allow for unwanted air movement
between the studs and the insulation. Always sta-

ple on the top of the stud; this will allow the batt
to completely fill any cavity into which it is
placed.

3. Not completely filling irregular areas--even small

voids in irregular framing or at the end of the batt
of 1-2% of the insulation area can result in a 25-
40% loss of R-value.

4. Not installing loose-fill cellulose to its proper den-

sity (fluffing).

In addition, the total R-value of a wall, ceiling, floor,
etc. will be different than the R-value printed on the
insulation because heat can be conducted through
studs and joists of the home (referred to as bridging
or short-circuiting the insulation). With careful
design and proper installation, short-circuiting can
be dramatically reduced.

Primary spaces in which to insulate your home are
shown in Figure 1 and include the attic, walls, floors,
and around the crawlspaces/basement. In order of

Insulation effectiveness

Where should insulation be applied in
the home?

All exterior walls

Basement

walls

Attic

= Insulation

Crawlspace

If basement is

fully insulated,

there is no need

for insulation here.

Floors over

unheated spaces

Crawlspace walls

Cathedral ceiling

Same as exterior walls

Figure 1. Places in the home where insulation should be applied

mining the minimum level of insulation (R-factor)
required for all areas of a home for three different cli-
mate zones in Kansas (shown in Figure 2). These
levels depend upon the type of heating system, fuel
used, and price of fuel/electricity. If the fuel/elec-
tricity price exceeds $6.50 per MCF of natural gas,
$0.60 per gallon of propane, or 5.5 cents per kilo-
watt-hour for electricity, use the "Better" level.

For example, a home in Topeka (central climate
zone) that has a natural gas furnace, basement walls,
and pays $6.00 per MCF could use the "Minimum"
insulation level which would be R-32 for the attic,
R-20 for floors over unconditioned spaces, and R-9
for basement walls. For additional information on
insulation in new home construction, consult the
Tips for Purchasing an Energy-Efficient Home
brochure at www.oznet.ksu.edu/dp_nrgy/ees.

What is the correct amount of insulation
required for your home?

Northwest

Central

Southeast

Minimum Better

Attic

Floor over unheated spaces

Walls

Foundation insulation

basement wall

crawlspace walls

slab-on-grade

priority, the attic, including the attic door or cover
hatch, should be insulated first followed by beneath
floors above unheated spaces, around walls in a heat-
ed basement or unventilated crawlspace, and around
the edges of slabs-on-grade, taking necessary precau-
tions to treat for termites.

In unfinished attic spaces, insulate between and over
the ceiling joists. In finished attic spaces, insulate
between the studs of "knee" walls, between the studs
and rafters of all exterior walls and the attic roof, and
on top of ceilings with any cold space above.
Insulate all exterior walls including walls between liv-
ing spaces and unheated garages, and the foundation
wall. For further information on foundation insula-
tion, refer to Foundation Insulation Fact Sheet at
www.oznet.ksu.edu/dp_nrgy/ees. Floors above cold
spaces such as crawlspaces, any portion of a room
that is cantilevered beyond the exterior wall below
(i.e., bay windows), and slab floors built directly on
the ground should definitely be insulated. Also,
extend insulation into the band joists to prevent air-
flow.

The correct amount of insulation required for a
home in Kansas is dependent upon location of the
home within the state (climate), how the home was
constructed, type and efficiency of the home's heat-
ing and cooling system, and type of fuel used to heat
the home. Guidelines have been established, and are
presented in Table 1, to assist homeowners in deter-

Northwest

Central

Southeast

Table 1. Recommended minimum and better levels of insulation (R-factor) in Kansas

Figure 2. Climate zone map

Many older homes contain less insulation than is rec-
ommended by today's standards. Unless your home
was recently built (1990 to the present), it would be a
good idea to check the amount of insulation in the
attic and walls. You can do this yourself simply by
measuring the thickness and identifying the type of
insulation used in each location. If your home was
recently constructed, the builder should be able to tell
you the level of insulation in each area of the home.
Otherwise, check the attic, walls, and floors adjacent
to the outside or unheated spaces like the garage, and
verify that the basement, crawlspaces, and walls are
insulated.

Where structural frame elements such as ceiling joists
and wall studs are exposed, it is simple to check insu-
lation. When walls are finished, it may be easier to
remove an electrical outlet on the wall (making sure
to turn off the power first) and shine a flashlight into
the cavity around the outlet box. When you have
determined the current level of insulation in your
home, compare it with recommended levels presented
in the section above. If insulation is absent or if lev-
els are significantly below recommended levels, con-
tact an insulation contractor about adding additional
insulation. Remember to insulate the attic first, fol-
lowed by the floors over unheated spaces, and then
walls.

Before insulation is installed in your home, either
during construction or as a retrofit, the home needs
to be checked for proper air sealing and moisture
control. Air infiltration into the living spaces of your
home, both in the summer and winter, can signifi-
cantly increase your monthly energy bills. In general,
insulation will not stop these leaks; therefore, taking
time to seal points of air leakage before installing or
adding extra insulation can result in big energy savings
as well as a more comfortable living space. For more
detailed information concerning air leakage and seal-
ing in your home, consult the Air Sealing Your Home
Fact Sheet available at www.oznet.ksu.edu/dp_nrgy/ees.

Control of moisture is also a major concern when
installing insulation because warm air inside the
home contains water vapor. If this vapor is allowed
to pass into or through the insulation and condense,
the insulation will lose its rated value, mold and
mildew may form causing indoor air quality prob-
lems, wooden structural members may rot, and exte-
rior paint will peel. Moisture moves throughout a
home with air and by diffusion, but air movement is
far and away the most important mechanism of
moisture transport within a home. Therefore, good
air sealing is extremely critical to controlling mois-
ture problems.

To restrict moisture diffusion insulation, use a vapor-
retarder paint (low permeability paint) or vapor bar-
rier that is installed on the warm side–the lived-in
side–of the space to be insulated.

Insulation usually comes in four forms–blankets and
batts, loose-fill blown-in or sprayed-in-place,
foamed-in-place, and rigid. Each type is made to fit
in a different part of your house. Table 2 presents
common types of insulation and important aspects
associated with their use.

■

BLANKETS, in the form of batts or rolls, are flex-

ible products typically made from fiberglass. Batts
are lightweight, fit standard floor joist and wall stud
spaces, are simple enough to install by yourself, and,
if installed carefully, will not slump or settle.

Continuous rolls can be hand-cut and trimmed to fit
and are available with or without vapor-retarder fac-
ings. Batts with a special flame-resistant facing are
available in various widths for basement walls where
the insulation will be left exposed.

Blankets do not, however, readily fit into irregular
spaces and can leave "insulation voids." If fiberglass
insulation is installed with voids, its performance
degrades substantially due to air convected around
and through the batts. Even small gaps in the insula-
tion will produce significant thermal degradation.
Therefore, it is extremely critical that fiberglass of
any form completely fill any cavity in which it is

What needs to be done before insulation
is installed?

Insulation forms and materials

Checking for the correct amount of
insulation in an existing home

installed and should not be covered with heavier
insulation or other materials which may compress it.
Figure 3 presents the correct installation of batt insu-
lation in the attic; Figure 4 illustrates the proper way
in which to install batt insulation with a vapor barri-
er attached.

R-values range from 3.2 to 4 per inch for batts and
most loose-fill insulation. Recent research indicates
performance of fiberglass degrades in cold weather
due to convective air movement. Adding a "cap"
layer of blown cellulose in the attic reduces this phe-
nomena. Fiberglass is an irritant to skin and eyes;
therefore, wear protective clothing when handling it.

Form

Method of Installation

Where Applicable

Advantages

Blankets and Batts

■

Fitted between studs,

■

All exposed walls,

■

Do-it-yourself

(Rolls)

joists, and beams

floors, and ceilings

■

Vapor barrier

Fiberglass

■

Suited for standard

Rock wool

stud and joist spacing,
which is relatively free
from obstructions

Loose-fill (blown-in)

■

Blown into place or

■

Enclosed existing wall

■

Commonly used

or Sprayed-in-place

spray applied by special

cavities or open new

insulation for retrofits

Rock wool

equipment

wall cavities

(adding insulation to

Fiberglass

■

Unfinished attic floors

existing finished areas)

Cellulose

and hard-to-reach

■

Spray-applied cellulose

places

and foam provide an air
barrier

■

Good for irregularly
shaped areas and
around obstructions

Foamed-in-place

■

Applied by professional

■

Exterior stud wall

■

High R-values and will

Polyurethane foam

applicator using special

cavities, irregular-

act as an air barrier

Isocyanurate foam

equipment

shaped shapes,
perimeter joist spaces

Rigid Insulation

■

Interior applications:

■

Basement walls

■

High insulating value

Extruded polystyrene

Must be covered with

■

Exterior walls under

for relatively little

foam (XPS)

1/2-inch gypsum board or

finishing (Some foam

thickness

Expanded

other approved

boards include a foil

■

Can block thermal

Polystyrene foam

material for fire safety

facing which will act as

short circuits when

(EPS or beadboard)

■

Exterior applications:

a vapor retarder.)

installed continuously

Polyurethane foam

Must be covered with

■

Unvented low-slope

over frames or joists

Polyisocyanurate foam

weather-proof facing

roofs

Table 2. Types of insulation – Basic forms and applications

Figure 3. Correct installation of batt insulation

■

LOOSE-FILL, blown-in insulation is comprised

of cellulose or loose fibers blown into building cavi-
ties or attics using special pneumatic equipment.
Blown-in cellulose can provide additional resistance
to air infiltration if the insulation is sufficiently
dense. This technique, refered to as "dense pack," is
often used to insulate and air seal existing walls.
Figure 5 shows loose-fill insulation being blown into
the attic.

Cellulose insulation is made from finely shredded
newsprint which is chemically treated to resist fire,
and fungal and insect growth. Properly installed
blown-in cellulose has an average R-value of 3.6 per
inch which is dependent on the chemical mix, paper
type, and its blown density. If the insulation is not
blown to manufacturer's recommended density,
settling will occur, gaps will form, and the intended
R-value will not be obtained. Cellulose must be
installed at a density of 3.5 to 4.4 pounds per square
foot to ensure it will not settle and that gaps do not
form. When having cellulose installed, always get
a written guarantee of settled depth from the
installer. When using cellulose in an attic, it should
not be covered with heavier insulation or other
materials which may compress it. Cellulose will fill
irregular spaces and will help minimize air move-
ment.

■

SPRAYED-IN-PLACE insulations are loose-fill

products such as cellulose, fiberglass, and mineral
wool that are mixed with an adhesive (usually water-
based) and blown into wall cavities. When properly
installed, wet-spray insulations will resist settling and
shifting, and allow the cavity to be completely filled.
Wet-spray cellulose reduces air movement, while
fiberglass and mineral wool don't.

Spray cellulose has an R-value of 3.5 per inch; blown
fiberglass 2.9 per inch, when blown to the proper
density; and mineral wool about 3 per inch.
Installation generally requires a trained contractor.

■

FOAMED-IN-PLACE polyurethane and isocya-

nurate foam insulations can be applied by a profes-
sional applicator using special equipment to meter,
mix, and spray into place. These foams also help to
reduce air leaks. Polyurethane foams can be used for
a variety of spray applications and are ideal for use
with irregular-shaped surfaces and narrow openings,
e.g., shim spaces around doors and windows. The
foam will act as an air barrier but not a vapor barrier,
and should be protected from prolonged exposure to
sunlight. When the foam is used in the interior of a
house, it must be covered with a fire-resistant materi-
al such as drywall. Polyurethane foam has an R-
value of 6.0 per inch.

Figure 4. Proper batt insulation installation with vapor barrier

Outside

Inside (warm side)

Vapor barrier

stapled to wall stud

Batt insulation

Wall stud

Isocyanurate foam is a semi-flexible, spray-applied,
plastic foam insulation best suited for use in exterior
stud wall cavities, perimeter joist spaces, and in small
and irregular shapes and areas such as shim spaces
around doors and windows. The material can be
used as an air barrier, but when installed on the inte-
rior of the house, it should be covered with a fire-
resistant material such as drywall. Installation
requires specially trained contractors. Isocyanurate
plastic foam has an R-value of 4.3 per inch.

■

RIGID INSULATION is made from fibrous

materials or plastic foams and is pressed or extruded
into board-like forms and molded pipe coverings.
These provide thermal insulation, strength with low
weight, and coverage with few heat-loss paths. Such
boards may be faced with a reflective foil that reduces
heat flow when next to an air space. Rigid foam
boards are made of polyisocyanurate, extruded poly-
styrene (XPS or blueboard), expanded polystyrene
(EPS or beadboard), 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 to be used in con-
fined spaces such as exterior walls, basements, foun-
dation and stem walls, concrete slabs, and cathedral
ceilings.

Polyurethane and polyisocyanurate insulations are
usually double-faced with foil, or sometimes come
bonded with an interior or exterior finishing materi-
al. The boards must be protected from prolonged
exposure to water and sunlight and, if used on the
interior, must be covered with a fire-resistant material
such as drywall. Due to the relatively high cost of
these insulations, use is generally limited to areas
which require a high R-value, but where space is very
limited. Faced boards have a typical R-value of 5.8
per inch to 7.2 per inch.

Extruded polystyrene (XPS)
is a lightweight foam plastic
board manufactured in low
and high densities suitable
for both above- and below-
grade applications.
However, the high-density
board should be used where
the material will be exposed
to relatively high pressures,
such as below a concrete slab
or in built-up roofing.
When properly installed, it
can act as an air barrier.
Low-density extruded poly-
styrene has an R-value of 4.7
per inch while high-density
XPS has an R-value of 5.0

per inch.

Expanded polystyrene (EPS) or "beadboard," as it is
often called, also comes in low- and high-density
boards. This high-density board is more moisture
resistant and can be used on the exterior of a founda-
tion, providing the surrounding soil is dry, sandy,
and properly drained. Low-density expanded poly-
styrene has an R-value of 3.7 per inch while the
high-density type has an R-value of 4.0 per inch. In
general, expanded polystyrene is less expensive than
extruded polystyrene or other rigid insulations.

Polystyrene will "break down" if left exposed to sun-
light for prolonged periods and must also be protect-
ed from solvents. If the insulation is to be used in
the interior of a house, it needs to be covered with a
fire-resistant material such as drywall.

Figure 5. Loose-fill insulation installation

Ducts of your heating and cooling system and water
lines of your home also need to be insulated.
Insulate those locations where ducts run through
unheated or uncooled spaces, such as an attic or
crawlspace. Heating and cooling ducts should be
insulated to R-6, but first check for air leakage in the
ductwork. Repair any leaks with water-soluble mas-
tic and embedded fiberglass mesh or metal-backed
tape (do not use duct tape as it will not stay in
place), then insulate the ducts with duct wrap insula-
tion. Piping can be insulated with conventional,
round, fiberglass insulation. Remember: simple duct
tape will not seal joints over an extended period.

Further information

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KS 66506–0124 (785-532-4392).

“This material was prepared with the support of the U. S. Department of Energy (DOE) Grant No. DE-FG48-

97R802102. However, any opinions, findings, conclusions, or recommendations expressed herein are those of the
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Printed on recycled paper

The following Web sites offer additional facts and
information on residential insulation:

■

www.ornl.gov/roofs+walls

■

www.epa.gov/energystar.html

■

www.eren.doe.gov/consumerinfo

For questions regarding this fact sheet or further
information on residential insulation, please contact
Engineering Extension at 785-532-6026. This fact
sheet is posted on the Kansas State University
Engineering Extension Web page at
www.oznet.ksu.edu/dp_nrgy/ees. Other KSU
Engineering Extension Fact Sheets posted at this site
include the following:

■

Tips for Purchasing an Energy-Efficient Home

■

Foundation Insulation

■

Selecting a Home Heating System

■

Selecting a Home Cooling System

■

Energy-Efficient Mortgages

■

Energy-Efficient Windows

■

Air Sealing Your Home

Other places to insulate in your home