Insulated Concrete Forms
You’ve probably seen them (if not used them yourself), foundations constructed with extruded polystyrene (type 2 Styrofoam) that gets filled with concrete. This type of foundation is more common than you may think and it’s being used more and more for houses and small commercial buildings. As a contractor, you need to be aware of this growing trend to use what are commonly known as Insulated Concrete Forms (ICFs).
Insulated concrete forms aren’t new – they’ve been around for more than 20 years. However, ICFs have become more prevalent because builders, engineers and architects want their structures to be stronger, more energy efficient and sound proof. This increase in usage has resulted in more companies now manufacturing insulated concrete forms including ARxx, QuadLok, Integraspec and Nudura. Personally, Nudura is the brand I use for both new construction and renovation projects, which I referenced in my article about how to choose the right home addition.
An Inside Look at Insulated Concrete Forms
ICFs consist two Styrofoam panels that vary in thickness depending on the manufacturer; the most common size is 2-1/2’. The two panels are connected by plastic webs. These webs are available in different widths depending on the thickness of wall being built. This compares to traditional foundations built using heavy plywood panels locked together using metal form ties, bars and stabilized with walers.
One of the main reasons insulated concrete forms are so popular is because of their R-value. Fortunately, the thickness of the walls doesn’t affect the R-value. Walls that are going to be under greater amounts of lateral pressure – whether from being below grade or high winds – require 8-10” thick concrete walls. A standard residential wall only needs six inches of concrete. Traditional foundations usually have 10” of concrete, which provides more strength, but if the same foundation uses insulated concrete forms and only has six inches of concrete it needs more rebar to prevent contractions that can cause cracks. Most ICF manufacturers have detailed reference charts that show rebar details based on the height and thickness of the wall. The manufacturers also may provide guides about how to construct rebar headers over rough openings. This can be done by building a buck to hold back wet concrete during the concrete placement stage.
Besides a good R-value, insulated concrete forms also come in a variety of different panel types to achieve different architectural details. For example, 90- and 45-degree corner pieces are used for both inside and outside corners. You also can order corner pieces that can be adjusted for unique angles. If the building has a brick face, you can use brick check panels designed to step out the form. In addition to connecting the panels, the plastic webs act as a stud and enable you to hang drywall directly on the face of the foam. This eliminates the need to frame wood or steel stud walls inside the structure. The webs also allow you to fasten plywood or furring strips, which then provide a nailing surface for siding.
Insulated concrete forms are much less labor intensive to both install and strip. As with any form, you need to brace the forms for pouring wet concrete. Most ICFs dealers sell a bracing system that both plumbs up and aligns the wall and acts as staging to work from while pouring concrete. When you start to strip the forms, all that has to be removed is the bracing. The foam in ICFs is permanent, but when using plywood panels you have to strip the panels, scrape them down and oil them.
Insulated concrete forms help with energy efficiency. Buildings constructed with ICFs are much more energy effiencient compared to traditional wood frames. For example, I recently worked on a 4,000 square foot vetrinary clinic. The clinic was upgraded from 800 square feet. We built
the clinic with insulated concrete forms; the owner said the heating expenses after the build were one-third of what she paid in her old space, even though the space was less than 25 percent of the size of the current building!
One final note about ICFs: They’re classified as “engineered,” which means there are strict engineering specifications that need to be followed in order for it to perform to a set standard. To ensure that the strict installation guidelines are met, whoever installs the forms must be licensed for that specific brand through training courses. If a licensed installer isn’t used on the build local building authorities can fail the project. Fortunately, dealers who sell insulated concrete forms offer the training courses.
Feel free to ask any questions about ICFs in the comments below and I’ll see if I can provide an answer.