What is the R-Value of Concrete? How to Maximize Wall Insulation with ICFs


Comparing insulation values can be confusing, but R-values are an opportunity to compare different materials in an “apples-to-apples” way. R-values can be incredibly helpful, because knowing what they mean and how to apply that knowledge is the key to maximizing insulation and choosing the right materials for a given project.

What is R-value?

Insulation types are rated using an R-value system. The R-value is a simple way for knowing how well a material insulates. The higher a material’s R-value, the better it is at insulating. Insulation is often sold at a given R-value, but materials should always be compared using R-value per inch.

Common Insulation Types

Many different types of insulation are available on the open market with some being higher performing than others. Here are some of the most common insulation types:


One of the most common types of insulation, fiberglass typically comes in either batt or loose-fill form. Batt fiberglass insulation has an R-value per inch of 3.1 to 3.4 while loose-fill fiberglass can range from 2.2 to 4.3 per inch of thickness. Fiberglass insulation makes up the bulk of insulation used in new home construction, accounting for 71% of insulation based on a 2018 report.

Expanded Polystyrene (EPS)

EPS foam is a lightweight, rigid type of foam board. The closed-cell nature of EPS keeps water absorption low and improves R-value. The R-value per inch of EPS can change based on the desired density of the foam, but it is typically in the 3.6 to 4.1 range.

Extruded Polystyrene (XPS)

Similar to EPS, XPS is made through a different manufacturing process to give it different material properties. EPS and XPS are both closed-cell types of foam, and XPS is considered a fully-closed matrix while substantial space exists between the cells in EPS foam. This variation makes XPS a stronger type of foam and better able to withstand water and other stresses. The average R-value per inch for XPS is usually around 4.7.

Polyisocyanurate (Polyiso)

Polyiso is often an expensive choice for insulation but it provides many exceptional performance characteristics. Exceptional compression strength, dimensional stability, and mold and chemical resistance make polyiso panels a routine choice for insulation placed in demanding locations like roofs. With an R-value per inch of 6 or greater, less thick insulation is needed to get the same total insulation performance.

Spray Foam

Unlike the batt or rigid board insulation types discussed earlier, spray foam is applied just like it sounds. Using specialized equipment, two chemical components are mixed as they are sprayed onto the wall. Once mixed, a reaction occurs that causes the material to expand. This expansion increases the thickness of the applied insulation and works to seal any potential gaps. Spray foam has R-values per inch ranging from 2.8 to 7, depending on the type of foam chosen.

Wall Assembly R-values

It is easy to assume that a wall’s R-value is equivalent to the insulation used in the wall, however, the truth is a bit harder to find. The insulation installed in the wall may have an R-value of 13, and a typical wood stud wall will have studs every 16” inches with insulation filling the cavity between the studs. These studs unfortunately have a lower R-value, meaning it is easier for heat to travel through these studs than it is through the insulation. This creates a thermal bridge which decreases the wall overall effective R-value.

Walls are made from many different components, so it is important to keep the entire wall R-value in mind. A wall’s composite R-value can be much lower after accounting for studs, fasteners, and installation techniques. It is the R-value of the entire wall that represents how well the building is insulated.

Fox Blocks ICF Walls Maximize R-values

Insulated concrete forms (ICF) are a great alternative to traditional wood or steel-stud construction. Consisting of two sheets of EPS foam held together by ties, ICF blocks are stacked on site to form a wall. Steel is added to the cavity formed by the blocks and then concrete is poured into the space. The resulting steel-reinforced concrete walls are not only strong enough to be used as a storm shelter, but they are also energy efficient.

Concrete has an R-value of between 0.1 and 0.2, but when combined with the built-in EPS foam, Fox Blocks boast an impressive R-value of 22. In addition to providing strong walls, ICF walls achieve such high R-values because of the different construction methods. Without studs to provide an easier path for heat to flow, solid ICF walls are more energy efficient. The continuous insulation on both sides of the wall enables the mass concrete to act as a 'thermal battery' retaining heat and controlling the temperature transfer through the assembly in cold or hot climate zones. Calculating the composite R-value for an ICF wall assembly compared to a traditional wall assembly shows that ICF performs better both in new construction, and after decades of use.

When it comes to maximizing R-value, ICF should be at the top of your list. To learn more about the R-value of concrete walls, reach out to the ICF experts at Fox Blocks.