Insulation Rating Guide: Understanding R-Values & Best Picks

Understanding R-values is crucial for choosing effective insulation. Higher R-values mean better thermal resistance, leading to lower energy bills and a more comfortable home.

Builder insulates the external walls with mineral sheet insulation in protective gloves. Thermal insulation work, house renovation.

When it comes to home energy efficiency, insulation is a crucial component.

The type of insulation you choose for your home can make an enormous difference in your energy bills and overall comfort.

One key factor to consider when selecting insulation is its R-value. But what exactly is R-value, and how does it affect insulation performance?

Insulation works by resisting the flow of heat, which naturally moves from warmer areas to cooler ones.

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The effectiveness of an insulation material’s resistance to heat flow is measured or rated in terms of its thermal resistance or R-value — the higher the R-value, the greater the insulating effectiveness.

Understanding R-values is essential to choosing the right insulation for your home.

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Basics of R-Value

The R-value is a measure of thermal resistance, indicating the capacity of an insulating material to resist heat flow.

The higher the R-value, the better the material insulates.

How R-Value Works

The R-value depends on the type of insulation, its thickness, and its density.

The R-value of most insulations also depends on temperature, aging, and moisture accumulation.

For multilayered installations, the R-values of the individual layers are added together to determine the overall R-value.

However, it’s important to note that insulation that is compressed will not provide its full rated R-value due to a phenomenon known as thermal bridging.

Importance of R-Value in Insulation

R-value is crucial in insulation as it directly impacts the energy efficiency of a home.

When insulation has a high R-value, it effectively traps heat in winter and keeps it out during summer, reducing the need for heating and cooling systems.

This leads to lower energy bills and a more comfortable home environment.

Different Types of Insulation

Rigid Foam Board Insulation

House rigid styrofoam insulation for energy saving

Rigid foam board insulation provides high R-values. They are commonly used in walls, roofs, and foundations for thermal insulation and to provide a degree of structural rigidity.


Worker placing styrofoam sheet insulation to the wall

Polystyrene is a common form of rigid foam board insulation. It is available in two types – expanded (EPS) and extruded (XPS).

EPS is less expensive and has a lower R-value per inch than XPS.

XPS provides a higher R-value and is often used for wall insulation, below-grade applications, and as attic insulation in some climates.


Polyurethane is another type of rigid foam board insulation with a high R-value, making it an excellent choice for insulating walls and roofs.

The R-value of closed-cell polyurethane insulation can drop over time as some of the low-conductivity gas escapes and air replaces it in a phenomenon known as thermal drift.

Most thermal drift occurs within the first two years after the insulation material is manufactured, after which the R-value remains unchanged unless the foam is damaged.


Polyisocyanurate, also referred to as polyiso, is a type of thermoset plastic typically produced as foam and used as rigid thermal insulation.

Its thermal performance is rated at a higher R-value per inch than other forms of insulation.

Other Types of Insulation

Beyond rigid foam boards, there are other types of insulation like spray foam, batts and blankets, loose-fill, and radiant barriers.

Each type has its own range of R-values and ideal use cases, from walls to attics to basements.

Choosing the Right R-Value

Typical recommendations for exterior walls are R-13 to R-23, while R-30, R-38, and R-49 are common for ceilings and attic spaces.

The amount of insulation or R-value you’ll need depends on your climate, the type of heating and cooling system, and the part of the house you plan to insulate.

To learn more, see our information on adding insulation to an existing house or insulating a new house.

Also, remember that air sealing and moisture control are important to home energy efficiency, health, and comfort.


R13 insulation is made from lower-density fiberglass and is typically used in walls that are 2×4 studs.

R19 insulation is made from higher-density fiberglass insulation and is typically used in walls that are 2×6 studs.


For crawlspaces, an R-value of R-19 is recommended. This helps prevent the cold ground temperature from affecting the temperature of the floor above.


Eco wool insulation is poured in the attic insulation roof for new home

If your attic has little or no existing insulation, you’ll want to install an R-38-rated material. If your attic has 2-3″ of existing insulation, you’ll want to install an R-30 to achieve a total of R-38.

If your attic has 5-6″ of existing insulation, you’ll want to install an R-19 to achieve a total of R-38.

Factoring Individual R-Values of Materials

When calculating the R-value of a multilayered installation, it’s important to add the R-values of the individual layers.

However, keep in mind that the overall R-value of a wall or ceiling may differ from the R-value of the insulation itself due to thermal bridging, where heat flows more readily through studs, joists, and other building materials.

Regional Influence on R-Value Choice

R-Value Zones within the US

The United States is divided into different climate zones, each with its own recommended R-values for insulation.

These recommendations are provided by the Department of Energy based on the specific climate conditions in each zone.

It’s important to consider your region’s climate when selecting the appropriate R-value for insulation.

Department of Energy’s Recommendations

The Department of Energy recommends higher R-values for colder climates, where insulation plays a crucial role in minimizing heat loss and maintaining comfortable indoor temperatures.

In warmer climates, the focus is on preventing heat gain and reducing cooling loads. Consulting regional guidelines can help determine the ideal R-value for your location.

Achieving Greater R-Values

house attic insulation - construction worker installing rock wool in mansard wall

Increasing R-Value in Attic Spaces

To achieve greater R-values in attic spaces, it’s essential to add insulation layers. If your attic has little or no existing insulation, installing an R-38-rated material is recommended.

However, if there is already some insulation present, you can choose a lower R-value insulation to reach the desired total R-value.

It’s crucial to consult with a local insulation contractor to determine the appropriate amount of insulation for your climate.

Improving R-Value in Exterior Walls

When it comes to exterior walls, the choice of insulation material and thickness can significantly impact the R-value.

Adding insulating sheathing can enhance the insulation performance of exterior walls.

Insulating sheathing helps reduce thermal bridging and improves energy efficiency.

Use of Insulating Sheathing

Insulating sheathing is a layer of insulation material applied to the exterior surface of a wall. It helps minimize heat transfer through the wall by providing an additional thermal barrier.

This can lead to improved energy efficiency and reduced heat loss or gain, depending on the climate.

FAQs on Insulation

What R rating should my insulation be?

The recommended R-rating for insulation depends on factors such as climate, type of heating and cooling system, and the part of the house being insulated.

Typical recommendations range from R-13 to R-49, with higher values needed in colder climates.

Is R30 better than R19?

When comparing R30 and R19 insulation, the choice depends on the existing insulation in your attic. If there is little or no existing insulation, R30 would be more effective.

However, if you already have 2-3 inches of insulation, adding R19 would achieve a total R-value of R38, which is the recommended level for attics.

Which is better R30 or R38?

Choosing between R30 and R38 insulation depends on the amount of existing insulation in your attic. If there is little or no existing insulation, it’s recommended to install R38 insulation.

However, if there is already 2-3 inches of insulation, adding R30 would reach the desired total R-value of R38.

Is R19 better than R13?

R19 insulation is made from higher-density fiberglass and provides a higher R-value compared to R13 insulation, which is made from lower-density fiberglass.

The choice between R19 and R13 depends on the size of the wall studs. R19 is typically used in walls that are 2×6 studs, while R13 is used in walls that are 2×4 studs.

Choosing the right insulation for your home is a crucial step in achieving energy efficiency and comfort.

By understanding R-values, considering regional climate recommendations, and factoring in the specific needs of different parts of your home, you can make an informed decision when it comes to insulation.

Remember to consult with professionals for personalized advice based on your unique circumstances.

With the right insulation and R-value, you can create a more energy-efficient and comfortable living space for years to come.

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