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What is the R-Value of Concrete?

What is the r-value of concrete?

What is R-Value?

The R-value is a measure of thermal resistance, which indicates how well a material can resist heat flow. The higher the R-value, the better the insulation and the more energy efficient a building will be. In the context of concrete, the R-value refers to its ability to resist heat transmission and is an important factor to consider when designing and constructing a building.

Concrete R-Value

The concrete R-value depends on its density and composition. Normal concrete slabs have an average R-value of 0.08 per inch, while high-density concrete has an R-value of around 0.1 per inch, and low-density concrete has an R-value of approximately 0.2 per inch. This means that the R-value of concrete per inch will vary depending on the specific type of concrete used.

Factors Affecting the R-Value of Concrete

The R-value of concrete is influenced by several factors, such as the concrete’s density, the type of aggregate used, the presence of air bubbles, and the amount of moisture present. Higher density concrete generally has a lower R-value, while lower density concrete has a higher R-value. Additionally, heat transmission is affected by the temperature difference between the interior and exterior of a building, the slab thickness, and the type of insulation used.

Concrete Slab Thickness

As the thickness of a concrete slab increases, so does its R-value. The table below provides a general idea of the R-value for various thicknesses of normal concrete slabs:

  • R-value of 1 inch of concrete: 0.08

  • R-value of 4 inches of concrete: 0.32

  • R-value of 6 inches of concrete: 0.48

  • R-value of 8 inches of concrete: 0.64

  • R-value of a 12-inch concrete wall: 0.96

Concrete Walls and Block Walls

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Concrete walls and block walls have different R-values depending on their thickness and construction. For example, the R-value of a 4-inch thick block of concrete is around 0.32, while the R-value of an 8-inch concrete block wall is approximately 0.64. A 12-inch concrete wall has an R-value of about 0.96.

Insulation and R-Value Enhancement

While the R-value of concrete alone may not provide sufficient insulation for a building, combining it with additional insulation materials can significantly improve its insulating properties. Some common insulation materials used with concrete include rigid foam insulation, spray foam, and vapor barriers.

Rigid Foam Insulation

Rigid foam insulation is a popular choice for use with concrete walls and slabs due to its high R-value and ability to resist heat flow. It can be installed on the exterior or interior of a building, providing additional insulation and increasing the overall R-value of the structure.

Spray Foam Insulation

Spray foam is another effective insulation material that can be used in conjunction with concrete. It is applied by spraying the foam directly onto the concrete surface, where it expands and hardens, forming a continuous layer of insulation. Spray foam not only increases the R-value of the concrete but also acts as a vapor barrier, preventing moisture infiltration.

Thermal Bridging and Insulating Capability

It is crucial to address thermal bridging when designing a building with concrete. Thermal bridging occurs when heat is transferred through building components with lower insulating capability, such as the junctions between walls, floors, and ceilings. This can lead to heat loss and reduce the overall effectiveness of insulation. To minimize thermal bridging, it’s essential to ensure that insulation is continuous and covers all potential areas of heat transfer.

Calculating the R-Value of a Building Component

To calculate the R-value of a building component, such as a concrete wall or floor slab, you can use the following formula: R-value = thickness (in inches) / thermal conductivity (Btu per hour per square foot per degree Fahrenheit). This calculation will provide you with a reasonable R-value estimation for the specific concrete used in your building project.

Additional Considerations for Insulation and R-Values

Beyond the choice of insulation materials, there are other factors to consider for achieving higher R-values and improved energy efficiency. These include:

  • Radiant heating: Installing radiant heating systems in concrete floors can help maintain comfortable temperatures and reduce heat loss.

  • Foundation wall insulation: Insulating the perimeter foundation walls can help prevent heat loss through the foundation and increase the overall energy efficiency of the building.

  • Living space insulation: Ensuring that living spaces have sufficient insulation will help maintain comfortable temperatures and minimize heat transfer between interior and exterior spaces.


Understanding the R-value of concrete and the factors that affect it is essential when designing and constructing a building. By selecting the appropriate concrete type, thickness, and insulation materials, you can create an energy-efficient and comfortable environment. Always consider additional factors such as thermal bridging and the insulation of living spaces to ensure optimal performance and energy savings.


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