Recomended Levels of Insulation: Your Guide to Insulation

Insulation level are specified by R-Value. R-Value is a measure of insulation’s ability to resist heat traveling through it. The higher the R-Value the better the thermal performance of the insulation. The table below shows what levels of insulation are cost-effective for different climates and locations in the home.

Zone Add Insulation to Attic Floor
Uninsulated Attic Existing 3–4 Inches of Insulation
1 R30 to R49 R25 to R30 R13
2 R30 to R60 R25 to R38 R13 to R19
3 R30 to R60 R25 to R38 R19 to R25
4 R38 to R60 R38 R25 to R30
5 to 8 R49 to R60 R38 to R49 R25 to R30
Wall Insulation: Whenever exterior siding is removed on an

Uninsulated wood-frame wall:

  • Drill holes in the sheathing and blow insulation into the empty wall cavity before installing the new siding, and
  • Zones 3–4: Add R5 insulative wall sheathing beneath the new siding
  • Zones 5–8: Add R5 to R6 insulative wall sheathing beneath the new siding.

Insulated wood-frame wall:

  • For Zones 4 to 8: Add R5 insulative sheathing before installing the new siding.

Unless you live in a newly constructed home built for energy efficiency, you would likely benefit from additional insulation. However, before adding insulation, you will first need to determine how much insulation you have already. To do this, you can hire a qualified energy auditor or go the do-it-yourself route.

The effectiveness of any type of insulation depends on a number of factors, including the following:

  • Proper installation of existing insulation
  • The materials your home is made of (i.e., brick, wood, etc.)
  • The climate inside and outside of your home
  • The types of heating, cooling and ventilation systems in your home

All of these factors must be taken into consideration in order to achieve the greatest energy efficiency.

The R-value

Insulation is assigned a resistance value, most commonly known as an R-value. An R-value is a measure of resistance to heat flow. The higher the R-value, the greater the resistance. R-values are established based on a type of material, its thickness and its density.

Heat Flows

Heat flows naturally from hot to cold wherever a difference in temperature exits. During the winter months, heat flows from heated living spaces to unheated indoor spaces and outdoors. A home heating system is used to compensate for the loss in heat. Conversely, heat flows from outdoors to cooler indoor spaces during the summer months. A home air conditioning system is then used to remove the heat. Insulation is an effective method of resisting heat flows in both directions.

If insulation is compressed, the actual R-value of an insulated component, such as a wall, will measure differently from the R-value of the insulation. Insulation is compressed when the installation allows for heat flows around the insulation, such as when it is installed between studs and joists.

Insulation Installation

Climate and structural composition are important in determining the proper method and type of installation. As an example, the US recommended levels of insulation that are most cost-effective for a retrofitted wood frame building located in various climates and locations around the country, shown above.


Even though insulation is used to prevent heat flows, a home needs ventilation (exchange of indoor and outdoor air) to prevent an accumulation of indoor air pollutants, excessive moisture, odors and health problems.

There are three basic types of ventilation:

  • Natural ventilation – an uncontrolled exchange of air through cracks, holes and vents
  • Whole house ventilation – a controlled exchange of air using fans and ducts
  • Spot ventilation – a controlled exchange of air, which is confined to spaces within the home. Spot ventilation is typically used in conjunction with one of the other types of ventilation to remove pollutants, moisture or odors at their source.
Recommended Ventilation Rate
The greater of:
0.35 air changes per hour
15 cubic feet per person per minute

Natural ventilation creates a problem when too much air is exchanged. When the weather is cold or it is windy outdoors, air exchanges may allow for much more air to enter the home than is necessary for ventilation purposes. Likewise, when it is hot and no wind is blowing, air exchanges may not allow for enough air to enter the home. This type of air infiltration may led to moisture control problems in a leaky home or health problems due to a flow or stagnation and build-up of mold and dust. In homes where natural ventilation is cause for air infiltration, controlled ventilation with air sealing should be implemented.

Air Sealing

Air sealing is a technique of sealing air leakages to prevent air filtration, such as with caulking or weatherstripping. Note that air sealing is not a substitute for insulation, but a technique to be used in addition to insulation. Insulation is used to resist heat flow while air sealing is used to restrict airflow, not necessarily heat flow. Techniques and materials for air sealing include caulking, weatherstripping, air barriers and an airtight drywall approach or simple caulk and seal technique,


Caulking is a method of applying a compound that forms a flexible seal into openings, such as holes, cracks and joints, which are less than one-quarter inch wide. Caulking provides structures with protection from water damage, both interior and exterior to the home. There are various types of caulking compounds available for use. The US Department of Energy (DOE) provides a comparison of caulking compounds as shown here:

Caulking Compounds

Caulking Compound Recommended Uses Cleanup Shrinkage Adhesion Cost Comments
Silicone: household grade Seals joints between bath and kitchen fixtures and tile. Forms adhesive for tiles and metal fixtures. Seals metal joints as in plumbing and gutters Dry cloth if immediate; mineral spirits or naphtha Little or none Good to excellent High Flexible: cured silicone allows stretch of joints up to three times normal width or compression to one-half the width
Silicone: construction


Seals most dissimilar building materials such as wood and stone, metal flashing, and brick Dry cloth if immediate; mineral spirits or naphtha Little or none Good to excellent High Permits joints to stretch or compress. Silicones will stick to painted surfaces, but paint will not adhere to most cured silicones.
Polyurethane, expandable spray foam Expands when curing; good for larger cracks indoors or outdoors. Use in nonfriction areas, as rubber becomes dry and powdery over time Solvent such as lacquer thinner, if immediate None; expands quite a bit Good to excellent Moderate to high Spray-foam quickly expands to fit larger, irregular-shaped gaps. Flexible. Can be applied at variable temperatures. Must be painted for exterior use to protect from ultraviolet radiation. Manufacturing process produces greenhouse gases.
Water-based foam sealant Around window and doorframes in new construction; smaller cracks Water None; expands only 25% Good to excellent High Takes 24 hours to cure. Cures to soft consistency. Water-based foam production does not produce greenhouse gases. Will not over-expand to bend windows (new construction). Must be exposed to air to dry. Not useful for larger gaps, as curing becomes difficult.
Butyl rubber Seals most dissimilar materials (glass, metal, plastic, wood, and concrete.) Seals around windows and flashing, bonds loose shingles Mineral spirits or naphtha From 5% to 30% Good Moderate to high Durable 10 or more years; resilient, not brittle. Can be painted after one week curing. Variable shrinkage; may require two applications. Does not adhere well to painted surfaces. Toxic; follow label precautions.
Latex Seals joints around tub and shower. Fills cracks in tile, plaster, glass, and plastic; fills nail holes Water From 5% to 10% Good to excellent Moderate Easy to use. Seams can be trimmed or smoothed with moist finger or tool. Water resistant when dry. Can be sanded and painted. Less elastic than above materials. Varied durability, 2 – 10 years. Will not adhere to metal. Little flexibility once cured. Needs to be painted when used on exteriors.
Oil or resin-based Seals exterior seams and joints on building materials Mineral spirits or naphtha From 10% to 20% Good Low Readily available. Least expensive of the four types. Rope and tube form available. Oils dry out and cause material to harden and fall out. Low durability, 1 – 4 years. Poor adhesion to porous surfaces like masonry. Should be painted. Can be toxic (check label). Limited temperature range.


Weatherstripping is a technique of using a specialized material to seal areas with movable joints, such as doors and windows. There are various types of weatherstripping designed to accommodate various types of friction, changes in temperature and weather as well as wear and tear. The DOE provides a comparison of weatherstripping materials as shown below:

Common Weatherstripping Techniques

Tension seal:Self-stick plastic (vinyl) folded along length in a V-shape or a springy bronze strip (also copper, aluminum, and stainless steel) shaped to bridge a gap. The shape of the material creates a seal by pressing against the sides of a crack to block drafts. Inside the track of a double-hung or sliding window, top and sides of door Moderate; varies with material used Durable. Invisible when in place. Very effective. Vinyl is fairly easy to install. Look of bronze works well for older homes. Surfaces must be flat and smooth for vinyl. Can be difficult to install, as corners must be snug. Bronze must be nailed in place (every three inches or so) so as not to bend or wrinkle. Can increase resistance in opening/closing doors or windows. Self-adhesive vinyl available. Some manufacturers include extra strip for door striker plate.
Plain or reinforced with a flexible metal strip; sold in rolls. Must be stapled, glued, or tacked into place. Seals best if staples are parallel to length of the strip.
Around a door or window (reinforced felt); fitted into a doorjamb so the door presses against it Low Easy to install, inexpensive Low durability; least effective preventing airflow. Do not use where exposed to moisture or where there is friction or abrasion. All wool felt is more durable and more expensive. Very visible.
Reinforced foam:
Closed-cell foam attached to wood or metal strips
Door or window stops; bottom or top of window sash; bottom of door Moderately low Closed-cell foam an effective sealer; scored well in wind tests. Rigid. Can be difficult to install; must be sawed, nailed, and painted. Very visible. Manufacturing process produces greenhouse gas emissions.
Nonporous, closed-cell foam, open-cell foam, or EDPM (Ethylene Propylene Diene Monomer) rubber
Top and bottom of window sash; doorframes; attic hatches and inoperable windows. Good for blocking corners and irregular cracks. Low Extremely easy to install. Works well when compressed. Inexpensive. Can be reinforced with staples. Durability varies with material used, but not especially high for all; use where little wear is expected; visible
Rolled or reinforced vinyl:
Pliable or rigid strip gasket (attached to wood or metal strips)
Door or window stops; top or bottom of window sash; bottom of a door (rigid strip only) Low to moderate Easy installation. Low to moderate cost. Self-adhesive on pliable vinyl may not adhere to metal; some types of rigid strip gaskets provide slot holes to adjust height, increasing durability. Comes in varying colors to help with visibility. Visible
Door sweep:Aluminum or stainless steel with brush of plastic, vinyl, sponge, or felt Bottom of interior side of in-swinging door; bottom of exterior side of exterior-swinging door Moderate to high Relatively easy to install; many types are adjustable for uneven threshold. Automatically retracting seeps also available, which reduce drag on carpet and increase durability. Visible. Can drag on carpet. Automatic sweeps are more expensive and can require a small pause once door is unlatched before retracting.
Works similarly to refrigerator gaskets
Top and sides of doors, double-hung and sliding window channels High Very effective air sealer
Tubular rubber and vinyl:
Vinyl or sponge rubber tubes with a flange along length to staple or tack into place. Door or window presses against them to form a seal.
Around a door Moderate to high Effective air barrier Self-stick versions challenging to install
Reinforced silicone:
Tubular gasket attached to a metal strip that resembles reinforced tubular vinyl
On a door jamb or a window stop Moderate to high Seals well Installation can be tricky. Hacksaw required to cut metal; butting corners poses a challenge.
Door shoe:
Aluminum face attachment with vinyl C-shaped insert to protect under the door
To seal space beneath door Moderate to high On the exterior, product sheds rain. Durable. Can be used with uneven opening. Some door shoes have replaceable vinyl inserts. Fairly expensive; installation moderately difficult. Door bottom planning possibly required.
Bulb threshold:Vinyl and aluminum Door thresholds Moderate to high Combination threshold and weatherstrip; available in different heights Wears from foot traffic; relatively expensive
“Frost-brake” threshold:
Aluminum or other metal on exterior, wood on interior, with door-bottom seam and vinyl threshold replacement
To seal beneath a door Moderate to high The use of different materials means less cold transfer. Effective. Moderately difficult to install, involves threshold replacement.
Fin seal:
Pile weatherstrip with plastic Mylar fin centered in pile
For aluminum sliding windows and sliding glass doors Moderate to high Very durable Can be difficult to install
Interlocking metal channels:
Enables sash to engage one another when closed
Around door perimeters High Exceptional weather seal Very difficult to install as alignment is critical. To be installed by a professional only.
Air barriers

Air barriers are materials used to prevent air leakage and control moisture. House wrap is a specialized material that is typically used as an air barrier. There are many different types of house wrap, but it typically consists of a fibrous spun polyolefin plastic that is matted into sheets and then rolled for transport. The wrap may include other materials to make it more tear resistant or weather resistant. Drywall, sheathing, decking and various other building materials that are used to build a structure also serve the purpose of air barriers.

Airtight drywall approach (ADA) and Simple caulk and seal (SCS)

ADA and SCS are wall construction techniques used to create a continuous air barrier. A continuous air barrier is a system in which all holes and seams are sealed throughout the entire structure. The ADA method provides for sealing throughout the home construction process. The SCS method provides for sealing to be accomplished after all exterior sheathing and drywall has been installed. Both techniques provide for interior drywall to be sealed to the building structure and for interior wall finishes and sheathing to be sealed to exterior framing.

Moisture Control

When air flows through a home, moisture (water vapor) travels with the airflow. Moisture also travels with heat transfers and it naturally diffuses through materials, but more than 98% of moisture travels with the airflow through a structure. Air moves from areas of high pressure to areas of low pressure via the easiest possible path. The easiest possible path in a home is usually through cracks and holes in the structure.

Dew Point & Relative Humidity

The temperature and moisture concentration at which moisture begins to condense is known as the dew point. The amount of moisture contained in air compared to the maximum amount of moisture that could be held by that same air, at the same temperature, is known as the relative humidity. The ability of air to hold moisture increases as the air warms and decreases as it cools. At the dew point, excess moisture that air can no longer hold condenses onto the first cold surface that it encounters. When that surface is a part of your home, damage, mold and mildew may form. When that surface is an exterior cavity of your home that has been insulated, the insulation and framing become wet.

In some homes, under certain environmental conditions, a vapor diffusion retarder (VDR), also referred to as a vapor barrier, may be used to reduce the amount of moisture flow. A VDR is a specially designed material that reduces the rate at which vapor diffuses (moisture moves) through a material. The unit of measure of the ability of material to retard diffusion is known as a perm. Any material with a perm less than 1 is considered an effective VDR. The installation of a VDR is dependent upon the climate. As such, it is not recommended or effective for all homes. The perm rating of some common building materials are shown below:

Perm Ratings of Building Materials

Material Perm Rating
Aluminum foil (1.35 mils) 0.05
Polyethylene plastic (6 mils) 0.06
Asphalt coated paper backing on insulation 0.40
Plastic coated insulated foam sheathing 0.40 -1.2
Vapor barrier paint or primer 0.45
Plywood with exterior glue 0.70
Drywall painted – latex paint 2-3
Drywall unpainted 50


Climate and the types of heating and cooling systems are taken into consideration when determining the R-value of insulation that should be used for a particular home. Climate is an important factor in insulation since climate directly affects the level of moisture in a home, and thus, dictates the type of insulation that should be used and the method of installation. Climate also dictates whether and how a VDR should be installed. A measure of climate, known as heating degree-days (HDD), is a measure of how often daily dry-bulb temperatures fall below a base of 68oF. HDDs are used to determine whether or not to install a VDR. The figure to the right shows where climate and geographical location affect the decision to install VDRs in regions of the US.

In cold climates that also get warm in the winter, a VDR should be placed on the interior walls of homes. In some southern states, a VDR should not be used and in the hot and humid regions, it should be installed on exterior walls. Under mild temperature conditions, any type of paint or coating serves as an effective VDR.

Assessing Existing Insulation

Information regarding the insulation in an existing home should be available from builders of newer homes, but if you have an older home, you will need to inspect the insulation or acquire the services of an energy auditor to determine information regarding the insulation. To perform your own home inspection you will need to determine if and where insulation exists and then determine the parameters that define the insulation. Parameters include the type, the R-value, thickness and depth of the insulation.


To inspect insulation, you will need to look for installation materials in attics, crawl spaces, basements and other spaces where insulation is the typical and visible. There are some places, such as the foundation, where insulation will not be visible. You will have to rely upon the builder, a previous owner or building permit documentation to assist you in determining whether insulation exists and then assist you in defining its parameters. Where insulation is visible, parameters of type, thickness and depth can be determined from visual inspection and measurement. After you have determined the necessary parameters, you may contact the US DOE for information on how to determine the R-value of the insulation. If you cannot find or determine the parameters of your insulation using the do-it-yourself method, you will need to consult the services of an energy auditor.

Energy Auditor

Energy auditors provide professional whole-house energy audits to determine how to make your home more energy efficient. In the process, they will access any existing insulation and determine the need, if any, for additional insulation. They use specialized techniques and equipment to:

  • Inspect the insulation
  • Access the need for air sealing
  • Determine the efficiency of your cooling system
  • Determine the efficiency of your heating system
  • Access the best ways to conserve hot water
  • Access the best ways to conserve electricity
  • Determine the extent of leakages and air flow losses

What Makes Insulation ‘Green’ ?

When properly installed, insulation, is green since it resists heat loss and reduces energy consumption in almost all aspects of your home. Properly installed insulation provides significant cost savings for gas, electricity, and water use, plus the benefits of adequate ventilation and moisture control.

Insulation can be installed in a variety of interior and exterior locations to a home from the foundation to the roof and around the entire perimeter. Insulation is most often be found in the following places:

  • Attic spaces
  • Attic access doors
  • Exterior walls
  • Foundations
  • Attic knee walls
  • Crawl spaces
  • Cathedral ceilings
  • Basements
  • Floors above unheated garages
  • Ducts in unconditioned spaces
  • Slab-on-grade floors.

Product Comparison

There are various types of insulation products and materials to serve a variety of uses as shown in the following chart. The method of installation and its benefit are also specified.

Comparison of Types of Insulation

Blanket (batts and rolls) FiberglassMineral woolPlastic fibersNatural fibers Unfinished walls, floors and ceilings Fitted between studs, joists and beams Standard do-it-yourself stud and joist installation
Concrete block Foam beadsLiquid foamVermiculitePerlite pellets Unfinished walls for new construction or major renovations Involves masonry skills Autoclaved aerated concrete and autoclaved cellular concrete masonry units have ten times the insulating value of conventional concrete
Foam board orRigid foam Polystyrene
Polyisocyanurate (Polyiso)Polyurethane
Unfinished walls, floors and ceilings.
Un-vented low-slope roofs.
Interior applications must be covered with 1/2-inch gypsum board or other building-code approved material for fire safetyExterior applications must be covered with weatherproof facing High insulating value for relatively little thicknessCan block thermal short circuits when installed continuously over frames or joists
Insulating Concrete Forms(ICFs) Foam boardsFoam blocks Unfinished walls for new construction or major renovations Part of the building structure Insulation is built into walls; creates a high thermal resistance
Loose-fill CelluloseFiberglassMineral wool Enclosed existing wall Open new wall cavities
Unfinished attic floors
Hard-to-reach places.
Blown or poured into place using special equipment Adding insulation to existing finished areas, irregularly shaped areas and around obstructions
Reflective system Foil-faced kraft paperPlastic filmPolyethylene bubblesCardboard Unfinished walls, ceilings and floors Foils, films, or papers: fitted between wood-frame studs, joists, and beams Do-it-yourself framing at standard spacing.

Bubble-form used if framing is irregular or if obstructions are present.
Effectiveness depends on spacing.
Most effective at preventing downward heat flow
Rigid fibrous (fiber insulation) Fiberglass
Mineral wool
Ducts in unconditioned spaces, plus other places requiring insulation that can withstand high temperatures HVAC contractors fabricate insulation into ducts Withstands high temperatures
Sprayed foam&Foamed-in-place CementitiousPhenolicPolyisocyanuratePolyurethane Enclosed existing wall cavities.Open new wall cavities.Unfinished attic floors. Applied using small spray containers.In larger quantities, applied as a pressure sprayed foamed-in-place product. Adds insulation to existing finished areas, irregularly shaped areas, and around obstructions
Structural Insulated Panels(SIPs) Foam boardLiquid foam insulation coreStraw core insulation Unfinished walls, ceilings, floors and roofs for new construction Connected together to construct a house Provides superior and uniform insulation compared to traditional construction methods and take less time to build

What To Look For

  • Airflow losses may contribute as much as 30% or more to your home heating and cooling costs.
  • Some state and local building codes dictate the minimum requirements for insulation products. You can always exceed the established minimums, but you cannot install products with lower ratings.
  • The US Government provides an online system to assist consumers with determining how much insulation to use and the best places to put installation in order to achieve maximum energy efficiency at
  • Fiberglass is the most commonly used type of insulation, particularly for do-it-yourself installations, but fiberglass insulation will not resist airflow losses, only heat flow losses. Other types of insulation are more effective at resisting both heat flow and airflow losses.
  • Fiberglass acts as a dirt filter. A visual inspection of any fiberglass insulation that shows dirty insulation suggests that it is not resisting airflows.
  • Be sure to differentiate water-based caulking compounds from solvent-based compounds before beginning to caulk. Solvent-based compounds require a solvent for cleanup.
  • Metal and vinyl weatherstripping are more durable and reliable than felt and foam weatherstripping, but there are health risks associated with vinyl.
  • Caulk and weatherstripping should only be applied to clean, dry surfaces for maximum effectiveness.
  • There is some controversy over potential health effects from fiberglass and cellulose installation materials. Issues include possible adverse effects of airborne fibers from fiberglass and gases from cellulose.
  • Cotton insulation is the latest development to watch for in insulation, and recycled denim is a popular choice.


Insulation provides such a great resistance to heat flows that properly installed insulation will provide great cost and energy savings. However, to achieve maximum energy efficiency, methods of moisture and airflow control also need to be implemented properly. Look for ENERGY STAR labeled products and materials to ensure maximum energy efficiency and durability. ENERGY STAR also provides comprehensive instructions for insulating and sealing air leaks, a process designed to make your home more energy efficient and quiet while also reducing the level of pollutants.


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