What is Home Insulation?

By Terry Schutz

| Published on Jun 7, 2023

Reviewed by Katie Barton

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Insulation helps regulate building temperatures and provides resistance to heat flow. Proper insulation makes for a more comfortable home and saves money on heating and cooling costs.

There are many types of insulation, ranging from spray foam to fiberglass batt insulation to reflective foil. The type you need depends upon your climate, home style, and installation location.

Why You Need Insulation: Understanding Heat Flow

Heat always flows from warmer to cooler areas in an attempt to make temperatures even. In winter, heat tries to escape the house, while on hot summer days, heat tries to move in.

Heat also flows between rooms – always from warmer areas to cooler areas, especially to unheated spaces like attics, basements, and attached garages.

As the heat moves throughout the home, your heating and cooling systems must replace the warmth or increase the cooling–spiking the cost of your energy bill.

How Insulation Works to Keep Your Home Efficient

Most insulation works by slowing conductive and convective heat movement. Radiant barriers and reflective insulation products reduce radiant heat gain. (To be truly effective, the reflective barrier has to face an air space.)

Knowing the definitions of the following terms can help you better understand home insulation:

Conduction. Describes the way heat moves through material, such as hot coffee heating a spoon.
Convection. Describes the way heat moves through liquids and gasses. Warm air rises, and denser, cooler air sinks toward the floor, which is why you may experience cold feet in the winter.
Radiation. Radiant heat travels in a straight line. It heats anything solid in its path, such as the heat from a hot drink, making the container uncomfortable to hold.

R-Values of Insulation

R-value is a measurement of the thermal resistance of insulative products. It measures the resistance to conductive heat flow. A higher R-value means a more effective product. R-values also depend on age, temperature, moisture, and insect/rodent infestations.

Some products like polyisocyanurate degrade over time and lose R-value. Other products, like blown-in loose-fill attic insulation, do not change R-value as they settle. Fiberglass insulation loses R-value as it is compressed and has about zero R-value when it becomes soaked. The value of fiberglass products is the dead air trapped in the product, and more compression or water equals less air.

A radiant barrier does not have an R-value because it does not absorb heat or conduct heat onward. Rather, these reflective barriers reduce heat by preventing it from passing through the structure.

The amount of R-value needed to provide comfortable living conditions depends on the climate of your location, the HVAC system in the house, and which parts of the house are being insulated.

Type and R-Value of Insulation by Climate Zones

The following climate zone map and tables help determine the types and amounts of insulation required for various locations in the house and for different situations.

Alaska climate zones:

7 – Aleutians East
7 – Aleutians West
7 – Anchorage
7 – Bethel
7 – Bristol Bay
8 – Denali
7 – Dillingham
8 – Fairbanks North Star
6 – Haines
6 – Juneau
7 – Kenai Peninsula
5 – Ketchikan Gateway
6 – Kodiak Island
7 – Lake and Peninsula
7 – Matanuska-Susitna
8 – Nome
8 – North Slope
8 – Northwest Arctic
5 – Prince of Wales-Outer Ketchikan
5 – Sitka
6 – Skagway-Hoonah-Angoon
8 – Southeast Fairbanks
7 – Valdez-Cordova
8 – Wade Hampton
6 – Wrangell-Petersburg
7 – Yakutat
8 – Yukon-Koyukuk

Zone 1 includes Hawaii, Guam, Puerto Rico, and the Virgin Islands.

CLIMATE ZONE	UNINSULATED ATTIC	3-4 INCHES OF EXISTING ATTIC INSULATION	UNINSULATED FLOOR	UNINSULATED WOOD-FRAME WALL
1	R30–R49	R19–R38	R13	R13 or R0 + R10 CI*
2	R49–R60	R38–R49	R13	R13 or R0 + R10 CI
3	R49–R60	R38–R49	R19	R20 or R13 + R5 CI or R0 + R15 CI
4 EXCEPT MARINE	R60	R49	R19	R20 + R5 CI or R13 + R10 CI or R0 + R15 CI
4 MARINE AND 5	R60	R49	R30	R20 + R5 CI or R13 + R10 CI or R0 + R15 CI
6	R60	R49	R30	R20 + R5 CI or R13 + R10 CI or R0 + R20 CI
7 AND 8	R60	R49	R38	R20 + R5 CI or R13 + R10 CI or R0 + R20 CI

*Note: In the table above, CI stands for “continuous insulation” that is applied to the exterior of the wall assembly just inside the cladding

Types of Insulation Materials

There are many types of insulation materials. All of them are effective at preventing heat loss, but some work better in certain types of situations.

Know the R-value you want to achieve and the ideal installation location–exterior, interior, between studs, etc. before choosing a product.

Between Stud Batts. Includes fiberglass batt insulation, rock wool batt insulation, wet or dry cellulose insulation, denim batt insulation, etc. These bulky products go in the wall cavities, where they are designed to resist conductive heat flow. They are available in multiple thicknesses and R-values.
Blown-In Loose Fill. Cellulose insulation, chopped fiberglass, or rock wool is blown into attics or wall cavities.
Rigid Foam Boards. Rigid foam insulation boards are applied over framing inside or outside the building. They provide an excellent R-value when glued to concrete walls and are used extensively on flat roofs. Gas trapped in rigid foam boards reduces conductive heat flow, insulating the house. Rigid foam boards are available in many thicknesses and R-values. R-5 to the inch is a fairly standard product, but less dense boards can provide less. Polyisocyanurate foam has an R-value of more than 5 to the inch.
Spray Foam. Wet spray foam applied into the wall cavities drys and seals all gaps, providing great insulation at R-5 per inch. The downside is that it doesn’t work well as a soundproofing material.
Reflective Foil. Highly reflective foils reflect radiant heat away from living spaces and are most effective in hot climates when applied to the exterior of a building. Reflective foils are often combined with rigid foam boards to provide increased R-value with a radiant barrier.