Insulated Concrete Forms (ICF) have become a relatively common way to build homes. This innovative building material is typically made of blocks of polystyrene foam with space in between to pour a concrete wall. Historically most commonly used for foundation walls, many builders are now taking ICF further and using them for above-grade walls of 1, 2, and 3 story homes. ICF Blocks made from non-polystyrene material can offer significant advantages over the more traditional EPS versions (more about this later!).
Is ICF Used In New or Existing Projects?
ICFs are found mainly in new construction rather than retrofitting projects. They are easy to install and have several advantages, including strength, durability, and ability to be well-sealed and well-insulated.
But just how sustainable are insulated concrete forms? Concrete requires more energy to produce compared to conventional wood-framed construction. However, operational energy also plays a significant role in the environmental impact of a building throughout its lifetime. In this article, we investigate the environmental effects of ICFs by examining the life cycle of this building material.
Above Grade Insulated Concrete Forms
What is ICF?
Insulated concrete form (ICF) is a system of blocks made from various materials (typically expanded polystyrene or EPS) where the blocks are stacked and filled with concrete and reinforcing. Instead of a traditional wood plank or plywood forms, the ICF blocks stay in place after the pour and provide a combination of insulation and surfaces ready for finishes.
Several steps of the construction process are consolidated as the insulation is included and no further wall construction is required prior to interior and exterior finishing. ICF walls are typically between 6″ and 16″ thick. Wall thickness will depend on the insulation level desired and the amount concrete required for structural strength.
Building with ICF Blocks
Photo Credit: Nexcem
Is an ICF Wall a Good Insulator?
The short answer is yes, but you need to look a bit further if you are building a sustainable, high-performance home. ICF construction has two advantages in terms of the energy performance of the building. First, it seals very well, preventing air leakage through the walls. Second, it has two continuous layers of insulation, one inside and one outside, with no thermal bridges. That reduces heat loss. Some ICF systems are intentionally designed with the majority of the insulation on the exterior face to maximize thermal mass or dynamic effects.
14″ R-28 Nexcem ICF Block with majority of insulation on the exterior
16″ R-36 Nexcem ICF Block
Is ICF Construction Less Expensive?
Overall, you’ll likely end up spending about 5% to 10% more in total construction costs than you would for a conventional wood-frame home. Although with lumber prices always on the increase, this premium is slowly shrinking year by year. Do keep in mind that the price of concrete can also fluctuate, and the price of your home is also dependent on the design, local construction labor costs, and additional factors.
It is also important to remember that the amount of time required to compile all of the necessary permits for an ICF home will likely take longer than for a conventional home. Since this is not the standard in the residential construction industry, the permitting process can be a bit more arduous. A licensed builder will likely be familiar with this process to make it a smoother (and hopefully quicker) experience and you will need a locally licensed engineer to design and stamp your drawings.
How Much Does ICF Save Over Time?
The savings and payback of an ICF home are primarily dependent on what you are comparing to and how well the home is built. If you have a home with an extremely tight building envelope, you will likely experience more considerable savings. While you will probably pay 5% – 10% more upfront for an ICF home, your energy bills will be lower each month than if you were to build a wood-frame home built to typical standards. Typically it takes about 5-7 years to recoup the initial upfront cost of building with insulated concrete forms
What is the Maximum R-Value of an ICF Wall?
ICF construction has two advantages in terms of the energy performance of the building. First, it seals very well, preventing air leakage through the walls. Second, it has continuous layers of insulation with no thermal bridges. This tight building envelope dramatically reduces heat loss.
Nexcem 16″ R-36
When building a high-performance house, like a Passive House, a typical off-the-shelf ICF system is often not thick enough. It may also struggle to meet the insulation standards in a cold climate like Canada or the northern USA. Fortunately, some ICF manufacturers have created products with an R-value of up to R-48 to address colder climates.
Basement built with Nexcem ICF Blocks 16″ R-28
You can also add more insulation to the outside to achieve the performance required by certain standards like Passive house.
On the above-grade walls, adding extra insulation to the inside can work better than the outside. And to make it easier, some companies now offer ICF options with thicker insulation.
Nexcem ICF Build. Photo Credit: Nexcem ICF
How Long Does ICF Last?
ICF homes have a lifespan of over 100 years, with minimal maintenance required as the foam will not degrade. It is also important to note that ICF homes can add increased protection during natural disasters. These homes perform well in flooding, so they are appropriate for coastal areas. The reinforced concrete also makes them suitable for highly seismic zones. Some builders can even ensure up to a 4-hour fire rating. If you live in an area that is prone to natural disasters, an ICF home could give you peace of mind.
Because of how durable ICF homes are, it does make remodeling difficult. If you foresee wanting to completely remodel your home at any point in the future, you might want to consider a more flexible building material.
Does ICF Need a Vapour Barrier?
ICF walls serve as vapor retardants, and as a result, do not need a vapor barrier. Other ICF systems like Nexcem are breathable and hygroscopic and all for the natural diffusion of vapor to create a regulated more natural humidity level and also don’t require a vapor barrier
Energy Comparison of ICF vs. Wood-Frame Homes
ICF Case Studies
Based on multiple research studies, it is apparent that ICF constructed homes have a lower environmental impact than traditional wood-frame construction.
One study compares the life cycle performance of a 3,600 square foot ICF house with a wood-frame house. The life cycle assessment (LCA) analyzed the following for both of these construction types:
The embodied energy of building materials
The construction process requirements
Disposal of the building materials
Global Warming Potential (GWP)
To address climate differences that can significantly change a building’s energy performance, the researchers examined two hypothetical homes. These homes would be built in five geographical locations in the United States and three locations in Canada. The wood-frame house was modeled to follow local building code requirements for each site, and the ICF home followed standards for ICF construction in each location. This approach allowed the researchers to draw meaningful comparisons between standardized buildings.
The study found that across all eight geographical areas, the life cycle performance of ICF homes was better after an assumed life cycle of 70 years. The total energy use reduction of ICF homes was between 4.8% and 12.7%, depending on geographical location and resulting climate. This study also found, like other similar studies, that operational energy use accounts for approximately 90% of a home’s environmental impact throughout its lifetime.
Another study compared an ICF building to a traditional wood-frame building, as well as a wood-frame building built to higher than average standards. These researchers found that while the initial energy input required for the ICF building was greater when looking at the entire life span of 100 years, the ICF building had a life cycle energy requirement that was 11% to 14% lower than both of the wood-framed buildings. They also found that the operational energy use was responsible for 95% to 97% of the entire environmental impacts for all three buildings.
Yet another study yielded similar results by conducting an LCA of an ICF home and wood-frame home in five US cities that represented a range of climate types (Miami, Phoenix, Washington DC, Seattle, and Chicago). They examined a typical size home at 2,450 square feet, which was very close to the average square footage of a single-family home at the time of the study. These researchers also found that the overall environmental impact of wood-frame homes was more significant than ICF homes. The study also provides an exceptionally robust review of construction types, study justifications, life cycle assessment considerations, and discussion of results.
Gables are also built with the ICF blocks.
Dave Phelps of ICF Homes of Virginia has witnessed similar results in building ICF homes. “For every three concrete houses we build, it uses the same amount of energy as one wooden house. So if we really want to look at energy efficiency for homes, 3 to 1 is an incredible ratio that we just can’t meet with building houses with wood.”
Overall, ICF homes increase your home’s comfort, reduce your monthly energy bills, and, most importantly, reduce your environmental footprint. ICF homes are considered high-performing due to their higher thermal resistance and thermal mass, along with stricter construction standards than are typically required for conventional wood-framed homes.
If you build a high-performance home that is insulated well above code to standards like the Passive House standard, your building will have a much lower energy footprint. That means lower energy bills and even greater sustainability.
If you choose ICF construction, ask for concrete with fly ash content, to make use of recycled materials. If you decide to go with wood-framed construction, look for FSC certified wood, sourced as locally as possible. To learn more about Nexcem, blown cellulose, and other kinds of insulation, see our installation guide.
Please contact Nexcem professionals for more information on building a net-zero energy home.