What in the world is ICF?

  • By Pablo Kanof
  • 17 Feb, 2017

If you have researched new home construction or energy efficient building practices any time recently, you’ve probably noticed the term “ICF” being thrown around a lot. So what is ICF? ICF stands for “Insulated Concrete Form.” ICF is an energy efficient wall construction material that has garnered quite a bit of interest in the building community over the last decade or so. It provides higher insulation values and enhanced structural strength compared to traditional construction materials, such as wood framing or concrete block construction.

How does ICF work?

ICF starts with a heavy duty H shaped nailing strip and rebar cradle. These are spaced every 8″ horizontally in each ICF block. A 2.5″ EPS (Extruded PolyStyrene, or styrofoam) panel is then attached to both sides of this nailing strips. You can see what the final product looks like in the adjacent picture. These blocks are then stacked, similar to Lego building blocks, to form the exterior walls of a home. Steel rebar is inserted both horizontally and vertically into the wall cavity as it is erected. Once the walls are fully erected and the door and window openings have been cut and framed out, concrete is poured. The entire wall cavity is filled with concrete and then vibrated to ensure that no air pockets remain in the wall. The thickness of this wall cavity is variable with the manufacturer of the ICF product. Here at Stewart Construction we typically use a   Fox Block   product with a 6″ cavity. Once the wall cavity has been filled with concrete and it has been given several days to cure, we remove the wall braces and are ready to continue with the construction process.

What are the benefits of using ICF?

There are three major benefits to using ICF: Insulation value, sound absorption, and structural strength. In this section we are going to review each of these benefits in detail.

Insulation Value

In Central Florida CMU (Concrete Masonry Unit) construction is the system most commonly used. We can directly compare the R-Value, which is a measurement of insulation effectiveness, of a CMU wall system to that of an ICF wall system. A standard 8″ thick CMU wall has an R-Value of 2.0. However, it’s fairly typical to install 1/2″ rigid insulation board over a block wall. This rigid insulation board has an R-Value of 3.2, bringing the total R-Value of the CMU wall to 5.2. The Fox Block ICF system has been   rigorously tested  to determine its effective R-Value. The EPS panels on the blocks have an R-Value of 10 each, the 6″ of solid concrete has an R-Value of .36, and these means the total R-Value of the Fox Block system is 20.36 alone.   This is a 391% increase in R-Value.What this means for a homeowner is that you will use less energy to heat and cool your home and you will retain heating and cooling much more effectively than in a traditional CMU home. In addition, an ICF home will require a smaller HVAC system to heat and cool.

Sound Absorption

Sound travels through materials in much the same way that heat does. Good insulating materials tend to absorb sound, and materials that are good at conducting heat also tend to transfer sound more readily. A typical ICF wall has 5 inches of EPS insulation and 6″ of solid concrete. A standard CMU wall has 1/2 an inch of EPS insulation, 2 1/2 inches of concrete, and a 5 inch air space. This should illustrate the drastic difference in sound transmission between ICF and CMU construction. While results are not entirely conclusive,   some tests show  that   ICF can reduce sound transmission 200% better than CMU.

Strength

The strength of ICF versus CMU should be fairly clear when you consider the way each system is constructed. CMU construction features hollow-core concrete blocks laid on top of each other. These blocks are fused to one another with mortar and then have steel rebar and additional concrete reinforcement inserted at key points, such as corners, door frames, and around windows. ICF construction features a solid 6″ thick concrete wall around the entire perimeter of the building. Furthermore, ICF is reinforced with steel rebar both vertically and horizontally.

When any structure faces stress, such as that from a hurricane, earthquake, or tornado, the weakest point is always at the joints in the structure. These joints are always where cracking and failure will occur first. In CMU construction there are joints between each individual 16″ x 8″ block. In ICF construction, because the wall cavity is filled with a solid pour of concrete, there are no joints. Period.   Conservative estimates show that a 6″ ICF wall is about 50% stronger than a CMU wall.

Conclusion

Here at Stewart Construction, we are believers in ICF. We know that this is the building system of the future and anticipate that eventually it will replace CMU construction as the dominant system in Central Florida. ICF is a superior product and we recommend it to every new homeowner that we meet with, and as you can see in our   Green Building Portfolio  many of them heed our advice and build for the future.

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