The Power of Insulated Concrete Forms: Maximizing R-Value in Your Construction Project


Insulated Concrete Forms (ICFs) are a popular building material that is growing in popularity. ICF blocks are well known for their exceptional insulation performance. To understand how well ICF compares to other types of insulation you’ll need the R-value. A standardized way for measuring insulation, R-values allow different types of insulation and building techniques to be quickly and easily compared to one another.


What is R-value?

In order to compare different types of insulation, there is a standard way to rate them, which is the R-value. A material’s R-value represents its ability to prevent the flow of heat. Materials with high R-values do a great job of blocking the flow of heat and are great insulators. Low R-value materials are not good for insulation.

Insulation is available in different thicknesses of the same type of material, so it often has an R-value per inch number associated with it. The R-value per inch will help you calculate how thick the insulation must be to meet the required R-value. If you need a higher R-value, either use a material with a higher R-value per inch or stack thicker pieces of materials that have a lower R-value per inch.

R-values help engineers and builders to more easily understand how much insulation a wall needs. For example, if a wall must have R-13 insulation, it may need 3.5” thick fiberglass insulation or just 2” of some polyiso insulation types, since polyiso is a better insulator. Knowing the desired R-value of the wall and the R-value per inch of insulation simplifies the entire process.

R-value and Walls

When building walls, materials like metal and wood are not great insulators. Because those materials are likely to transfer heat, it is necessary to add insulation to slow down that heat transfer. How the insulation is applied has a great deal of impact on the overall R-value of the wall assembly.

Insulation is typically added in one of two ways: cavity insulation or continuous insulation.

Cavity Insulation

When building a typical wall with studs, a cavity naturally forms between the studs and the exterior sheathing. This cavity can readily accept insulation and is standard building practice for many builders. The downside of cavity insulation is the studs and headers.

Since the insulation is broken up by studs and headers, heat can flow around the insulation through those components. For example if R-13 cavity insulation is used, the overall wall will have an R-value lower than R-13. With metal studs, the overall R-value can be considerably lower. These types of breaks in the insulation are called thermal bridges and they greatly reduce the insulation’s effectiveness.

Approximately 25% of typical wood framing has thermal bridging. The installation of batt insulation in the cavity is also susceptible to poor installation techniques which leave air gaps or compressed batts which account for a 30%+ reduction in the walls R-value efficiency.

Thermal bridges occur not only in studs and headers but also in fasteners used to attach the insulation to the cavity. Metal fasteners act as tiny thermal bridges, each creating a path for heat to travel through the insulation. Even though fasteners are small, the many fasteners used in an entire building can add up to have a significant impact on the overall R-value.


Continuous Insulation

To overcome the effect of breaking the insulation, engineers and architects developed continuous insulation methods. Continuous insulation goes on a building’s exterior sheathing and completely envelops the building. Continuous insulation reduces the thermal bridging effect of cavity insulation, and a building with continuous insulation will have a higher R-value throughout the wall. Building codes now require continuous insulation to combat thermal bridging.

ICF Construction and R-Value

ICF construction utilizes continuous insulation while making it incredibly easy. ICF blocks consist of two 16" x 48" panels of foam insulation, held together with ties to form a block with a hollow space between the insulation. The blocks are stacked together onsite to form walls and other features. Rebar is placed in the hollow space in the blocks and then filled with concrete and allowed to cure.

Once the concrete cures, the result is an incredibly strong and energy efficient steel-reinforced concrete structure. The building has two built-in layers of continuous insulation; one on the inside and one on the outside. These two insulating layers allow the mass concrete to act as a thermal battery controlling the temperature change across the wall assembly. The design of ICF blocks also prevents thermal bridging through the wall assembly. ICF from Fox Blocks even boasts an impressive R-value of R-22.

Building codes recognize the thermal efficiency of the overall wall assembly. This allows a simple Fox Blocks wall assembly to be evaluated with an overall wall R-value of R-24. The addition of the Fox Blocks Energy Stick can enhance the R-value to over R-30.


ICF: Exceptional Insulators

ICF blocks outperform most traditional construction techniques due to their simplicity of installation and exceptional thermal performance. ICF blocks produce buildings with impressive overall R-values and very low energy usage. When choosing between building materials, be sure to check out the advantages of ICF blocks.

To learn more about R-values and ICF blocks, reach out to the insulation experts at Fox Blocks today!