Thursday, August 12, 2010

The Basics of Insulating Concrete Form Construction Technology

Insulating Concrete Forms, also known as ICF construction, is a concrete building system that offers superior strength, energy efficiency, durability and comfort compared to traditional construction methods. Although it has been predominantly used in the residential market during the past decade, commercial applications are rapidly increasing.

There are several other concrete home building systems, including masonry, reusable forms and pre-cast products. This article focuses on ICF technology and not on any specific manufacturer in the ICF industry.

ICF construction technology is not smoke and mirrors. It is a very proven product in a new package. Simply put, it is a reinforced concrete wall identical to the ones that have been designed for years as basements, foundations and retaining walls. The advantage is that the forming system is very lightweight, has high insulation properties and does not require removal. The finished wall generally incorporates integral attachment points for interior and exterior finishes.

With an ICF wall, the forms are stacked, the walls are braced and aligned and the concrete is placed in the stay-in-place form. The wall is simply a monolithic concrete core (just like any other concrete wall), with two continuous insulation layers. The faces (AKA flange) of the ties function as the furring strips for attaching interior and exterior finishes.

The initial idea for insulated block construction has been around for over 50 years. In the 70's, polystyrene foam was introduced. NAHB (National Association of Home Builders) performs an annual survey of residential builders across the US. According to their research, the market has exploded during the past 5 years. The ICFA (Insulating Concrete Forms Association at reported that 16 percent of all new custom home starts in 2004 used ICF technology and the industry is growing by over 30% per year.

Conceptually, ICF technology is rather simple. They all use the same basic components including a face shell of expanded polystyrene foam, a core of reinforced concrete and a plastic form tie that supports the face during concrete placement. The foam panels are typically fully reversible, 2.5" thick by 16" tall by 48" in length. The plastic ties are typically 6" on center which provides incredible stability during concrete placement. The ties are embedded ½" inside the foam panel and their position is marked on the foam panel so installers can easily find them. The foam provides an R-22 continuous insulation plane from the footing to the top plate.

The concrete in an ICF wall is nothing special. Design specifications are typical of conventional foundation requirements. The one minor difference is the aggregate size. It is typically 3/8" pea gravel to allow for easy and smooth pumping of the concrete, especially for above grade applications.

Concrete placed inside an ICF actually achieves much higher than normal and specified strength. This is due to the ideal curing conditions, stable temperature and slow moisture loss rates inside the expanded polystyrene panels.

There are currently over 70 manufacturers of ICF's in the market around the US. I always get asked the question "Which one is the best?" The answer I always give is "Which is better, a Ford or a Chevy?" Depending on who is asking, I have the following responses:

Homeowner: It shouldn't matter to you. From a user's perspective, all ICF brands perform dramatically better than frame construction under every circumstance. The differences between brands will not be noticeable to you. You should perform standard due diligence and locate the best contractor and let the contractor use the product that he and his crew is most comfortable using.

Contractor: Here the differences are the greatest and affect the type and amount of labor required for installation and also the waste factor. Some brands require more on-site labor, others have a lower material and/or shipping cost. Others are pre-assembled to minimize on-site labor. Some forms have waste percentages approaching 10%, while others are closer to 1%. It really depends on personal preference and experience of the construction crew.

Architect: Cavity configuration affects the structural performance slightly, but all ICF brands have load-bearing and shear strength capacities far exceeding frame walls (up to 600% greater in some cases). As a designer, the biggest concern is the web tie face size and web tie spacing. (Example, vertical lap siding may require additional furring if the tie face is vertically oriented and has a wide spacing). It is worth noting that the placement of windows, doors and T-walls can be affected by web tie spacing. Typically, flat wall ICF products with closer web tie spacing require significantly less attention to these details.

I suggest contacting the Insulating Concrete Forms Association via the internet to obtain a list of primary members. These are some of the largest and best established companies. Like most any construction product you specify, whether it is plumbing, lumber, or windows, it is the local people providing the support and service that always make the biggest difference. Other valuable sources of reliable and non-biased information include:, It is worth noting that there are many other excellent resources available via the internet and that I don't own or control any of the websites listed in this article.

There are three interior core configurations of ICF's. Flat wall is a simple vertical section of uniform thickness and is the easiest to engineer and install. Waffle grid has vertical and horizontal cores - alignment of cores must be maintained by installers, but uses about 25% less concrete than flat wall. The thin web section is about 2" to 3" thick. Screen grid has same alignment requirements of waffle grid and utilizes a field installed spline between blocks for finish attachment. All three types are included in the Prescriptive Method for ICF Wall Design and the International Residential Code (IRC 2006) and concrete walls are typically all designed and engineered according the ACI 318. However, the newest engineering code standard, ACI 560, will no longer provide engineering data for waffle or screen grid ICF products.

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